Lay Summaries

The summaries below are provided by our authors to help put their research into context for the wider scientific community and the general public. Lay summaries for the current issue are here. You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

Lay summaries for the current issue.

 

You can also find all the previous lay summaries by issue, as well as summaries for articles on Early View, in the lay summaries archive.

 

Links between minimum and maximum energy expenditure in animals

Sonya K. Auer, Shaun S. Killen and Enrico L. RezendeHummingbird feeding. Photo provided by authors.

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Does an idling Ferrari consume more fuel than a Volkswagen Beetle? A similar question applies to living organisms. Whether at rest or active, animals are constrained to operate within the energetic bounds determined by their minimum and maximum metabolic rates, which can differ considerably among individuals and species. The floor and ceiling of metabolic capacity in an animal may be mechanistically linked to each other if the former reflects the idling cost of the machinery needed to support the latter. A Ferrari, for example, needs a larger engine to attain a higher top speed than a Beetle, but this engine may cost more to run even when the car is not moving. In animals, increased muscle mass and other biochemical features that support high levels of activity may similarly increase resting costs. Here we conduct the first comprehensive assessment of the relationship between minimum and maximum metabolic rates across a diversity of vertebrate taxa (fish, amphibians, reptiles, birds, and mammals), analysing 176 published estimates of their correlation across individuals within a species and 41 estimates of their correlation across species. We found a general positive association between minimum and maximum metabolic rate that is shared among all vertebrates, suggesting that Ferraris such as hummingbirds or cheetahs spend more fuel at rest than Beetles such as chickens or sloths. In other words, power can be costly. This finding has major implications for our understanding of how different lifestyles evolve: while it may be advantageous to be highly active to search for food or capture prey, there also seems to be a high price to pay while at rest. In fact, some researchers speculate that this cost-benefit relationship underlies the evolution of warm-blooded birds and mammals whose metabolism at rest is so high that they can produce enough heat to remain warm at cold temperatures. Our results suggest that minimum and maximum metabolic rates are functionally linked and evolve together, providing some support to this hypothesis.

Image caption: Hummingbird feeding. Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Lianas may have considerable contribution to forest water dynamics with small basal stem area

Ryuji Ichihashi, Chen-Wey Chiu, Hikaru Komatsu, Tomonori Kume, Yoshinori Shinohara, Makiko Tateishi, Kenji Tsuruta, Kyoichi Otsuki.A liana in the forest canopy. Photo by Ryuji Ichihashi.

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Plants absorb water from the ground and release it into the air from the leaves (transpiration) in exchange for CO2 uptake. The amount of water transpired from the vegetation is an important factor of the water cycle, affecting, for example, local climate and the water resources available to neighbouring societies.

Lianas (woody vines) are a peculiar yet important component of forests. They climb neighbouring trees to attain higher positions, and display their leaves in the forest canopy, yet their basal stems remain quite thin. Lianas have a much greater amount of leaves relative to their basal stem area (BA, through which water flows), compared with trees. The top-heavy architecture implies that lianas possibly consume more water through transpiration than expected from their BA. Here, we evaluated the contribution of lianas to community-level canopy transpiration in a warm temperate forest stand, and discussed the potential importance of lianas to forest water dynamics.

We measured the rates of water ascent in the stems (sap flux) for 1 year for four species each of lianas and trees using a thermal dissipation method (based on empirical relationships between the extent of heat dissipation from the sensor and the water-flow rates surrounding the sensor). Lianas showed an average of 2–4 times greater sap flux per unit stem area than trees throughout the year. By extrapolating the sap flux data to the inventory data of the study plot, we estimated that lianas contributed 12.8% to the annual stand transpiration while comprising only 2.3% of stand BA.

Our results indicate that the contribution of lianas to forest water dynamics may be several times greater than their contribution to forest BA. This implies that a slight increase of liana abundance might have considerable effects on water dynamics and, through competition with trees for limited water, the capacity of forests to store carbon. The enlargement of liana communities has already been observed across neotropical forests. This study underlines the necessity of evaluating the relative importance of lianas to forest water dynamics in forests worldwide.

Image caption: A liana in the forest canopy. Photo by Ryuji Ichihashi.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Parasites getting into trouble in murky waters

Alexandre Budria Large-scale phytoplankton bloom is a sign of eutrophication. The photography was taken from a plane over the Baltic Sea in August 2015. The trail left by a cargo ship that passed through the bloom (left side) attests of the impressive scale of the phenomenon. Credit: Alexandre Budria.

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Eutrophication is a type of water pollution caused by human activities, such as intensive agriculture or waste discharges, which notably stimulates the growth of microalgae and makes the water murky. Nowadays, this disturbance constitutes a major threat to most water bodies because it causes direct changes in aquatic ecosystems, including excessive algal growth, health problems linked to the toxicity of the introduced pollutants (various forms of nutrients like nitrates and phosphates) and harmful algal blooms, as well as more complex and indirect changes, such as modifications of the food chain, loss of large plants, increased turbidity and oxygen depletion. It is commonly assumed that wildlife health declines as water condition deteriorates, favouring parasite outbreaks in eutrophied areas. However, parasites themselves can also be affected directly by eutrophication. Accordingly, eutrophication can both enhance and prevent parasite transmission, inducing both positive and negative effects on the health of aquatic organisms. Care should thus be taken when predicting the ultimate consequences of eutrophication on parasites. In this synthesis, I discuss how the different changes induced by eutrophication in water bodies can influence infections by presenting studies conducted on the topic for a variety of organisms, ranging from viruses infecting microalgae to worms that travel via the food chain to successively infect snails, frogs and birds. In spite of the large number of publications currently available in the scientific literature, much remains unknown concerning the effects of eutrophication on parasitic diseases, as illustrated by the knowledge gaps identified in this review article. Future directions for research should notably include investigations on the possible synergies between the different changes caused by eutrophication in aquatic ecosystems, the behavioural responses of wildlife that might influence parasite transmission, and large-scale monitoring of parasites. Stronger collaborations between aquatic ecologists and disease ecologists are necessary to predict outbreaks in eutrophied areas and, hence, improve wildlife management.

Image caption: Large-scale phytoplankton bloom is a sign of eutrophication. The photography was taken from a plane over the Baltic Sea in August 2015. The trail left by a cargo ship that passed through the bloom (left side) attests of the impressive scale of the phenomenon. Credit: Alexandre Budria.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

How come similar lizards coexist? Towards a functional understanding of species coexistence

Anamarija Žagar, Miguel A. Carretero, Al Vrezec, Katarina Drašler, Antigoni KaliontzopoulouDifference in how strong are the bites (bite force) and how fast can they climb (climbing speed) for two lizard species that look remarkably similar on the outer appearance but with subtle differences in functional traits found ways to coexist in a geographical area. Symbols for females are circles and for males are squares. Photo credits: Miha Krofel.

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We examined how is it possible that two lizard species that are at first sight remarkably similar in their outer appearance can coexist and live together in the same geographical area. Usually, morphologically and ecologically similar species in areas of geographical overlap (sympatry) come into competition that could result in segregation or differentiation – one species either moves away or changes to use a different part of the ecological niche. In our particular study system, there is no definite pattern of spatial segregation or differentiation in morphology and species share the study area, occurring either in single-species or two-species populations that are mostly in the dispersal ability range of both species. We were interested how functional morphology and whole-organism performance plays a role in promoting this observed pattern of coexistence. Thus we measured morphological traits, the strength of bite and the speed of running and climbing of males and females of both species. The biggest difference between species was found in two functional traits, bite force and climbing speed, which were also linked with corresponding morphological traits. The species with larger and taller heads exhibited stronger bite forces and females had longer trunks that reduced climbing speed. Stronger bite forces and larger heads may potentially promote segregation between species in dietary preferences since the lizard with stronger bite could eat harder prey. On the other hand, the lizard with a flatter head could use narrower crevices, hence, have a better chance to escape predators that search for them inside shelters. Stronger bites and larger heads also provide one species with a dominant position in male-male combats that lizards engage in to defend their preferred area for e.g. basking, moving, seeking females etc. Moreover, lower climbing speeds in females with longer trunks may lower their anti-predator escape abilities, but could on the other hand positively influence reproductive effort. Our results exemplify how important it is to focus on the functionality of traits when we are trying to understand the observed community structure in nature. It is not only the variation in outer appearance, but the functional diversification that is responsible for the complexity of community structure via coexistence.

Image caption: Difference in how strong are the bites (bite force) and how fast can they climb (climbing speed) for two lizard species that look remarkably similar on the outer appearance but with subtle differences in functional traits found ways to coexist in a geographical area. Symbols for females are circles and for males are squares. Photo credits: Miha Krofel.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Patterns of prey capture by penguins are influenced by the patchiness of their prey

Gemma Carroll, Martin Cox, Robert Harcourt, Benjamin J. Pitcher, David Slip and Ian JonsenPenguin capturing prey.

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In many natural systems, prey is distributed patchily across the landscape. Dense groups of individual prey items are clustered within patches of lower prey density, that are in turn separated by areas where prey is scarce. This is the case in the open ocean, where marine predators are faced with the challenge of finding prey that is both patchy and constantly on the move. We looked at spatial patterns of prey capture by the smallest penguin species – the little penguin – in south eastern Australia. While we tracked the penguins with GPS and acceleration devices that could identify prey capture, we also surveyed their feeding area from a small boat with an acoustic ‘fish finder’ to independently examine the distribution of their prey. We found that overall, there was a “match” between where penguins foraged and where there were shallow schools of prey. This was related to features of the marine environment that might help penguins find prey, such as water temperature and salinity. We found that the distances between two consecutive prey capture events by a penguin occurred on two scales: a short scale (less than 10 m) that corresponded to the size of prey schools, and a larger scale (more than 50 m) that corresponded to movements between prey patches. This gives insight into how predators move around and find prey when it is distributed in patches. Finally, we found that there were features of individual schools that helped penguins catch prey, with penguins catching more prey in areas where schools were dense, compact and shallow. Our study shows that foraging by predators is finely tuned to the patchiness of their prey at different spatial scales, and helps us to understand the strategies that animals have evolved to find food in complex environments.

Image caption: Penguin capturing prey.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Benefits of thermal tolerance plasticity

Alex R. Gunderson, Michael E. Dillon and Jonathon H. StillmanPhoto provided by authors.

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It has long been known that animals can physiologically adjust to changing temperatures (without evolutionary change), a process known as “thermal acclimation.” It is generally assumed that thermal acclimation is beneficial, but it has proven difficult to empirically demonstrate the benefits, if they exist, under natural conditions. This is a pressing issue given that human-driven climate change is causing environmental temperatures to rise across the globe, and acclimation has the potential to mitigate the effects.

We estimated the benefits of acclimation for the heat tolerance of 103 ectotherm populations (“cold-blooded” animals including reptiles, insects, and amphibians) by comparing overheating risk under natural thermal variability, assuming animals can acclimate, relative to overheating risk assuming that that they cannot acclimate. Our analyses combined experimentally measured heat tolerance plasticity for each population with decades of habitat temperatures measured at weather stations near each population.

We found that acclimation can reduce the overheating risk of ectotherm populations; however, we also found that the benefits of acclimation are “incomplete.” This means that as temperatures rise, plasticity cannot prevent the overheating risk of populations from increasing. Acclimation is therefore not a “silver bullet” that will allow animals to overcome the detrimental effects of global warming.

Image caption: Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Plant defense negates pathogen manipulation of vector behavior

Baiming Liu, Evan L. Preisser, Xiaobin Shi, Huaitong Wu, Chuanyou Li, Wen Xie, Shaoli Wang, Qingjun Wu, Youjun Zhang Whitefly is feeding on the abaxial side of a tomato leaf.

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Many important and economically-damaging plant pathogens are transmitted by insect vectors, and pathogens have been shown to alter vector behavior in ways that promote both their uptake and transmission. In the Tomato yellow leaf curl virus (‘TYLCV’)- Bemisia tabaci-Solanum lycopersicum (whitefly-tomato) interaction, Bemisia-vectored TYLCV transmission has resulted in massive economic loss in China and elsewhere. While TYLCV-mediated changes in Bemisia feeding have been shown to improve the likelihood of viral uptake and transmission, the ability of plants to defend themselves against such manipulation has not yet been explored.

We found that high concentrations of jasmonic acid (JA), a chemical elicitor of plant defense, prevent TYLCV from manipulating Bemisia behavior, thereby reducing viral infection in the plant. We used both transgenic plants (in which the ability to make JA had been suppressed) and normal plants treated with jasmonic acid demonstrate that virus-infected Bemisia fed much more than uninfected whiteflies on JA-suppressed and control plants, but similarly to uninfected whiteflies on high-JA plants. In a follow-up experiment, we found that Bemisia transmission of TYLCV yielded lower infection levels in high-JA plants than in normal or low-JA plants. When we directly injected TYLCV into plants, however, high- and low-JA plants had similar infection levels. The ability of JA to negate pathogen manipulation of vector behavior appears to constitute a hitherto-unknown means of plant defense.

The long co-evolutionary history of many plant-vector-pathogen complexes suggests that this phenomenon may be widespread in both natural and managed ecosystems. Identifying how plants defend themselves against vector manipulation also provides a novel starting point for research aimed at managing pathogen outbreaks in agricultural systems.

Image caption: Whitefly is feeding on the abaxial side of a tomato leaf.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Understanding the role of animal defecation in aquatic nutrient cycles

Halvor M. Halvorson, Delaney J. Hall, and Michelle A. Evans-WhiteLondon Creek, the source stream for aquatic macroinvertebrates. Photo credit: Hal Halvorson.

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A central question in ecology is how organisms affect the ecosystems they inhabit. Ecologists have historically addressed this question from many angles; one of the most compelling over the last two decades has been a focus on animal wastes. This is because wastes depend on diets and vary widely across animal species, leading to substantial diversity, and when wastes are released, they enter the environment and affect ecosystem processes including the transformation and transport of nutrients. In aquatic settings like streams, animal wastes predominately occur as faeces and excreta, released in particle and dissolved forms respectively. Previous research has focused on animal excreta because these dissolved wastes - especially ammonium and phosphate - are nutrient-rich and highly bio-available for uptake. Through excretion, animals can be substantial sources of dissolved nutrients in many ecosystems.

Animal faeces are a different form of waste that, compared to excreta, are less bio-available and more nutrient-depleted, but may still be ecologically important because many animals defecate substantial material (many times their own body weight) during their lifespan. However, we poorly understand whether defecation serves as a “source” (net production, as in the case of excretion) or a “sink” (net storage or loss) of nutrients in ecosystems. In our study, we collected 3 different co-occurring stream macroinvertebrate species - the stonefly Allocapnia, the cranefly Tipula, and the isopod Lirceus - and fed them low- or high-nutrient leaf litter. We then collected their faeces and compared faecal nutrient contents as well as release and uptake of dissolved nutrients as faeces decomposed over several months. We found that both diet and source animal affected faecal nitrogen and phosphorus contents, ammonium release, and uptake of nitrate over time. Importantly, we found that animal faeces can remove dissolved nutrients from the water column due to microbial uptake, serving as sinks, in direct contrast to net production of dissolved nutrients by animals via excretion. These findings are helpful to understand how animals may affect their ecosystems by changing nutrient cycling.

Image caption: London Creek, the source stream for aquatic macroinvertebrates. Photo credit: Hal Halvorson.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

"Cagey" trees have safer lives

Tristan Charles-Dominique, Jean-Francois Barczi, Elizabeth Le Roux and Simon Chamaillé-Jammes  Image provided by authors

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Where large browsers such as impalas or kudus are abundant, trees survive only if they have chemical or structural defences. Structural defences include the arrangement of dense and intricate architecture, termed ‘cage’ architecture. Previous studies showed that trees developing in herbivore-rich environments tend to have more cage architecture, but its precise effect on mammalian herbivores remains unknown. In this paper, we test experimentally how cage architecture affects the bite rate of goats, a generalist mammalian herbivore. We selected 11 palatable tree species with contrasting architectures and described their ‘caginess’. Lastly we evaluated how the caginess of trees affects herbivores when feeding on the inner leaves in tree crowns. We observed that the bite rate of goats on inner leaves of the cagiest trees was so severely reduced that they could not satisfy their daily nutritional requirements. We discuss how this could affect the preference of wild herbivores for less cagey trees, especially at the end of the dry season.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

How does prey abundance influence sexual size dimorphism in tropical snakes?

Gregory P. Brown, Thomas R. L. Madsen, Rick ShineTwo species of frog-eating snake show different patterns of sex-specific growth plasticity in response to prey abundance. In Keelback snakes (left) females grow faster when frogs are abundant but males do not. In Slatey-grey snakes (right) both sexes increase growth rate when frogs are abundant. Photo credit G. P. Brown.

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In most animals males and females differ in body size; sometimes males are the larger sex and sometimes females are. The difference in size between males and females (called the degree of Sexual Size Dimorphism or SSD) is thought to reflect a disparity in the costs and benefits of large body size between the sexes. Large body size might be a benefit if it lets you produce more eggs, or win more fights against rivals. But it may also be a cost if it makes you more visible to predators or requires more food to maintain.

We studied two species of tropical snakes to determine if the ability of males and females to grow rapidly during periods of high food abundance reflected the benefits that large size held for them. Both snake species preyed on frogs. In Slatey-grey Snakes, males and females increased growth rate to the same extent when frogs were abundant. In this species, both males and females have higher reproductive success if they are big. Large males father more offspring than smaller ones and large females produce more eggs and larger eggs than small females do. In Keelback snakes, females grow faster when frogs are abundant but males do not. In this species larger females also produce more and larger eggs than small females, but large males are unlikely to have higher reproductive success than small males. This sex-specific growth plasticity in Keelbacks could contribute to temporal or spatial variation in SSD.

We found that the extent to which snakes utilize prey resources for growth depends on how much their reproductive success is enhanced by being large. Thus previous levels of prey abundance can partly shape the extent to which SSD is expressed in wild populations.

Image caption: Two species of frog-eating snake show different patterns of sex-specific growth plasticity in response to prey abundance. In Keelback snakes (left) females grow faster when frogs are abundant but males do not. In Slatey-grey snakes (right) both sexes increase growth rate when frogs are abundant. Photo credit G. P. Brown.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

To know a scorpion by its tail; the tail strike of scorpions differs between species in shape and speed

Pedro Coelho, Antigoni Kaliontzopoulou, Mykola Rasko and Arie van der MeijdenScorpion with stinger trajectory traced. Photograph provided by authors.

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There are almost 2,500 species of scorpions in the world, and many differ in the shape and size of their venomous tail*. The reasons for this large variation in tail shape are often not known. While scorpions sting their insect prey slowly and precisely, they defend themselves from attackers with a fast and swooping strike of their tail. The defensive strike may therefore be the more demanding behavior that a scorpion performs with its tail. In this study we measured the strike speed of scorpions for the first time. We also investigated if there are differences in the arc that the stinger, which sits at the end of the tail, describes during such a defensive strike.

We recorded the tail strikes of scorpions using high-speed video, and reconstructed the stinger’s trajectory in 3D. Comparing the 3D shapes of the strikes of seven different species, we found that there are differences between the species. However, some very similar species did not differ in the shape of their tail strike. We also compared the well-known and dangerous “fat-tailed scorpion” to a close relative with a much less thick tail. These two species did show differences in the shape of their tail strike and also differed in the maximum speed of the strike, with the fat-tailed scorpion being the faster one.

Some tail strikes were “closed”, almost returning to the start position, while others were more “open”, with the start point and the end point further from each other. More “open” shapes were faster that more “closed” shapes.

Our results show that species, body size, and tail thickness and length, may be important factors in determining the shape, speed and acceleration of the defensive tail strikes of scorpions.

*It should be noted that the “tail” of a scorpion is really a continuation of its body, with only the stinger at the end being the true tail.

Image caption: Scorpion with stinger trajectory traced. Photograph provided by authors.
Read the article in full here.

 

The triangular seed mass-leaf area relationship holds for annual plants and is determined by habitat productivity

Bianca A Santini, John G Hodgson, Ken Thompson, Peter J Wilson, Stuart R Band, Glynis Jones, Mike Charles, Amy Bogaard, Carol Palmer & Mark Rees Photo provided by authors.

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The relationships between plant traits tells us about the amount of resources species invest on a given trait. For example, thicker leaves are long-lived, but their construction is expensive for the plant and have lower photosynthetic rates than thin leaves. Another example, related to our study, is the triangular relationship found between seed mass and leaf area in woody species. This relationship tells us that small-seeded species can have either small or large leaves, whereas big-seeded species have large leaves. However, the combination of big seeds with small leaves does not occur. Again, this give us insights into resource allocation, in this case of the photosythates in a leaf and how are they distributed, either into small seeds or big seeds.

Indeed, resource allocation changes from species that live longer to those with shorter life-spans, and this will be reflected in the relationships between plant traits. For this reason, in this study, we wanted to know if the triangular relationship for seed mass and leaf area found in woody plants holds for annual species, which reproduce and die within a year, and invest most of their resources on reproduction. To test this, we used 401 annual species and, importantly, we incorporate indicators of habitat productivity and light into our study to test if these influence the relationship between these two traits.

Surprisingly, we found that the triangular relationship between seed mass and leaf area holds for annual species, and that the productivity of the habitat is driving this relationship. This is that in more productive habitats species with big leaves can either have either small or big seeds, whereas in low-productive habitats, species can only have small seeds and leaves. This suggest that in more productive habitats, which are also more competitive, species have more strategies for seed size/number selection. Our results show that despite the differences in their life cycle, plants conserve similar strategies across different life-forms, and that the productivity of the habitat plays an important role by driving and selecting for leaf and seed size.

Image caption: Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

How do temperate trees maintain or restore water transport function in overwintering stems?

Cun-Yang Niu, Frederick C. Meinzer & Guang-You HaoPhoto by Miao Wang.

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Keeping the integrity of water transport via the water-conducting xylem vessels is crucial for trees. But a great challenge to temperate trees is to maintain hydraulic function in overwintering organs, due to freeze-thaw cycles that they normally experience. As the air-saturated sap in xylem conduits freezes, air bubbles are formed due to the insolubility of gases in ice. Upon thawing, small bubbles would collapse due to surface tension but large bubbles may expand to fill the whole conduits and hence block the water transport through these conduits, especially if the water columns in the conduits are under a relatively large tension. This process is known as freeze-thaw induced embolism and the sensitivity of xylem to such dysfunction is positively correlated with xylem conduit size. In stems of some tree species with relatively large conduits, a single frost can cause almost total loss of water transport function. Although embolism may not harm trees during the dormant season, it may cause severe damage or even tree death during the following growing season. Some tree species depend on strong resistance to freeze-thaw induced embolism by producing conduits of smaller size, but that will unavoidably compromise their efficiency of water transport. Some other trees simply abandon old conduits for water transport and almost totally depend on new conduits formed in the early spring. In many temperate trees species, the ability to generate positive xylem pressures, including root pressure and stem pressure, has evolved to facilitate the dissolving of air bubbles in winter-embolized conduits. It has been shown to be an effective mechanism to refill winter-embolized vessels in some tree species; however, the potential impact of such a dramatic change of life history on adaptation of temperate trees is under studied. Using a common garden setup, we specifically compared the water-transport-related characteristics of species having positive xylem pressure with those that don’t have this ability. Contrasts observed between functional groups in these functional traits indicate that positive xylem pressure may have partially freed some temperate tree species from adaptive constraints imposed by winter embolism formation.

Image caption: Photo by Miao Wang.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Competition during thermoregulation – The costs of being (or not being) under the spotlight

Travis W. Rusch and Michael J. Angilletta Jr.Male mountain spiny lizard (Sceloporus jarrovi) basking under heat lamp in laboratory thermal arena.Photo Credit: Travis W. Rusch.

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Animals spend much of their time keeping themselves at the right temperature (i.e. thermoregulating) to maximize performances such as digestion, growth, and locomotion. For most species, the primary means of thermoregulation is shuttling between sun and shade. However, because temperature varies throughout space and time, organisms regularly compete for access to suitable microclimates, especially when these resources are rare. Such competition is costly, as competing individuals lose opportunities to thermoregulate, risk injury from fighting, and may experience hormonal changes. Often, features such as body size determines the outcome of competition, with larger individuals gaining greater access to resources. Thus, the costs of competition are often greater for smaller individuals.

In this study, we used heat lamps to investigate the behavioural and physiological costs of competition for mountain spiny lizards by observing the behaviors of solitary or paired males in thermal gradients. When paired, large males outcompeted small males for access to a heat source. Surprisingly, this behavior caused large males to thermoregulate less accurately and less precisely. This result likely occurred because larger males increased their use of the heat lamps in the presence of a small male. In fact, some of the large males allowed their temperatures to approach the lethal limit before leaving the heat source. Conversely, small males experienced lower body temperatures when paired with a large male, because males prevented them from regularly accessing the heat source. Competition also caused a stress response in the form of elevated corticosterone in both large and small males, though this effect was much larger in small males. Lastly, competition caused changes in testosterone in both large and small males, but in opposite directions. Large males tended to increase testosterone while small males decreased testosterone after being paired. Therefore, both large and small males incurred costs of competition for a limited heat source, including reduced thermoregulatory performance and greater physiological stress. These results highlight that thermoregulatory behavior is influenced by both abiotic and biotic factors, such as available thermal resources and competitors.

Image caption: Male mountain spiny lizard (Sceloporus jarrovi) basking under heat lamp in laboratory thermal arena.Photo Credit: Travis W. Rusch.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Neighbor effects on tree architecture: functional trade-offs balancing crown competitiveness with wind resistance.

David W. MacFarlane, Brian KaneThe architecture of a tree is shaped by its genetics (center tree is a maple) and the influence of surrounding trees. Photo by David W. MacFarlane.

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Each tree has a unique architecture defined by different arrangements of the major parts: trunk, branches, leaves. Tree architecture is partially defined by what species the tree is; an expression of its genetics. For example, pine trees have their branches arranged in whorls around the stem. However, tree architecture is also plastic—trees grow adaptively to match the changing environmental conditions that the tree is exposed to over its life span. So, there is a lot of variation within species that is not well documented. It is generally understood that shading from other trees and wind pressure are major forces shaping tree architecture. Trees must grow taller and arrange their branches and leaves to capture enough light energy to survive, in competition with neighbors. However, they must also adopt a wind-stable growth form or risk stem breakage or toppling over and uprooting under wind pressure. We were interested in determining the tradeoff between optimizing architecture for light capture versus wind resistance, looking at trees growing in the open versus growing in the forest with differing levels of crowding from neighbors. To study this we analyzed measureable tree- and branch-level architectural traits of four temperate, broad-leaved, deciduous tree species of differing shade tolerance and wood strength from multiple locations across the northeastern United States.

Our results show that differences within species, due to the effects of crowding from other trees, were much stronger than differences between species and locations. Open-grown trees developed relatively large crowns and branches and a squat growth form suitable to resist greater wind exposure. By contrast, increasing light competition from neighboring trees caused forest-grown trees to become increasingly more spindly in the main stem, with slender branches sparsely distributed over a disproportionately large crown volume—presumably to maximize light capture. Though the latter is an intrinsically less wind-stable form, it can be adopted to increase light capture, because neighboring trees reduce exposure to the wind, which should greatly reduce the likelihood of stem breakage or uprooting under critical wind pressures.

Image caption: The architecture of a tree is shaped by its genetics (center tree is a maple) and the influence of surrounding trees. Photo by David W. MacFarlane.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Immunocompetence in a long-lived ectothermic vertebrate is temperature dependent but shows no decline in older adults

Laura M. Zimmerman, Amanda Wilson Carter, Rachel M. Bowden, Laura A. VogelPhoto provided by authors.

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In ectothermic (cold-blooded) vertebrates, temperature affects all of the body’s functions, including immune function. Age is a second factor that can affect immune function in vertebrates. Typically, the immune system gets worse with age in vertebrates. But it is unknown if these factors, age and temperature, can have interacting effects on the immune system. We set out to test this using the red-eared slider turtle as our model system. The immune functions that we tested involved B cells, a type of white blood cell. In turtles, B cells can produce antibodies in the presence or absence of antigen stimulation. Further, they can also engulf potential pathogens through a process called phagocytosis. We tested the ability of B cells from sliders to produce antibodies and phagocytose antigens at varying temperatures that the turtles would experience in nature.

We found no interaction between age and temperature on any of our measures of B cell function. However, we did find a significant effect of temperature, with decreased function at temperatures below 29°C. Interestingly, we did not find any negative impact of age on the measured immune functions. This rather unusual finding warrants more investigation into the immune responses of the red-eared slider turtle.

Image caption: Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Co-existence with non-native brook trout breaks down the integration of phenotypic traits in brown trout parr

Libor Závorka, Barbara Koeck, Julien Cucherousset, Jeroen Brijs, Joacim Näslund, David Aldvén, Johan Höjesjö, Ian A. Fleming, Jörgen I. JohnssonEcologists at work. Photo provided by authors.

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Humans have introduced a variety of species outside their native ranges. Some of these species establish in the new environment successfully and can subsequently change the ecosystem. However, some of the effects of invaders are difficult to monitor but may have serious long-term impacts, such as population declines or extinction of native species.

Natives challenged by the presence of invaders often respond by changing traits. These traits, which can be physiological, morphological or ecological, are often associated together and there is some evidence that these trait associations are adaptive. For example, individuals that are active often have a high metabolism, which allows them to process food rapidly and maintain their elevated activity. In contrast, a high metabolism can be disadvantageous for inactive individuals, as they may not be able to find enough food to sustain themselves. An invader may affect these adaptive associations between traits by changing food distribution or activity of native individuals.

Here we test the idea that invasive species can break down adaptive associations among the traits of the natives, thereby reducing their growth rate. We used a wild population of brown trout living in a small Swedish stream, which was also occupied by non-native brook trout in the upstream stretch. Combining laboratory measurements of behaviour, metabolism, and body shape with observations of the movement and diet of individual fish in the wild, we tried to evaluate if and how trait associations were affected by the presence of the invader.

We found that associations between traits generally were weaker in brown trout living together with invasive brook trout than in brown trout living alone. When together with brook trout, brown trout consumed more terrestrial prey, and had smaller home ranges and a stouter body shape, changes that were associated with a reduction in growth. On the basis of these results, we suggest that the presence of invasive species can break down adaptive associations among traits in native species. Our results can help to explain other cases where invasive species reduce survival or growth of native species, even when direct effects like competition or predation are not observed.

Image caption: Ecologists at work. Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Log moisture and moss growth under thinned and unthinned forest canopies

Sean R. Haughian and Katherine A. FregoImage provided by authors.

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Water availability is important for mosses, because they do not have roots; they simply absorb liquid water (directly through their leaves) from rainfall, dew, and surface flow. Many different species of moss seem to prefer living on rotting logs, and scientists have often attributed this tendency to the logs acting as moisture reservoirs: the logs absorb water when it is raining, and release water when it is not raining, thereby ensuring that the mosses on the surface stay moist for much of the time. However, nobody has ever tested whether rotting logs actually supply water to the mosses that grow upon them.

We tested how well a log-dwelling species of moss grows on a series of artificial logs in which we had changed the volume of water they could hold, and compared them to natural rotting logs. We expected the artificial logs with the largest water capacity would produce the most moss growth. This test was done in a forest in Atlantic Canada, in two forest types: a dense spruce forest and a more open spruce forest. We also measured the surface humidity of these logs before and after watering, to see if water capacity was related to surface humidity.

We found that the mosses grew best on natural logs, in the more open forest. Among artificial logs, we found that mosses grew better on logs with small water capacities than those with large capacities. This was despite the fact that logs with a larger water capacity also had a more humid surface.

We concluded that logs probably do not supply much moisture to the surface, at least not enough to support moss growth. Instead, we think that precipitation is the most important source of moisture for log-dwelling mosses. Nevertheless, the fact remains that many moss species prefer to live on rotting wood; we propose that rotting wood may actually help mosses remain moist by allowing small puddles to form on its surface. Beyond that, other aspects of rotting wood, such as nutrient content or longevity, may explain this pattern, but require further tests.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Home-field advantages of litter decomposition increase with nitrogen addition

Ying-Bin Li, Qi Li, Jun-Jie Yang, Xiao-Tao Lü, Wen-Ju Liang, Xing-Guo Han, T. Matijn Bezemer Photograph provided by authors.

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Due to fossil fuel combustion and agricultural practices, atmospheric deposition of nitrogen (N) has increased over the past decades, and is projected to increase further in coming years. N-deposition often leads to changes in soil biological communities, plant litter and soil characteristics. And all these changes in litter quality, soil abiotic factors, and the composition of the decomposer community will interact to influence decomposition processes in terrestrial ecosystem. Recently, some studies have shown that litter decomposes faster in its habitat of origin than in other habitats. This is called the “home-field advantage” (HFA) effect. However, our knowledge about the relative role of litter quality and soil characteristics in litter decomposition and HFA effects is still limited, especially under long-term N deposition.

To investigate this question, we collected soil and two types of litter (monospecific and mixed species litter) from a long-term N-deposition field experiment with seven N-addition treatments. We examined the effects of N-addition on litter quality and soil characteristics. We then carried out a three-pronged microcosm decomposition experiment with (i) litter from different N-addition treatments decomposed in a standard field soil; (ii) standard litter decomposed in soils from the different N-addition treatments; and (iii) litter decomposed in soil from the same N-addition treatment plot.

Our study shows that N-addition greatly influences litter decomposition and increases the HFA effect via changes in the quality of litter and the soil characteristics. Local litter decomposed faster than standard litter on its home soil, and local litter decomposed faster on home soil than on a standard soil as indicated by positive “litter effects” and “soil effects”. The results of our study suggest that the effects of N-addition on the soil characteristics appear more important for decomposition than its effects on litter quality. Nitrogen deposition is an important threat to ecosystems worldwide and our study emphasizes that ecosystem functions such as decomposition can be greatly influenced by these global changes.

Image caption: Photograph provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Oxidative status and fitness components in the Seychelles warbler

Janske van de Crommenacker, Martijn Hammers, Jildou van der Woude, Marina Louter, Peter Santema, David S. Richardson and Jan KomdeurPhoto provided by authors.

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An important ecophysiological trade-off is oxidative stress: the balance between damaging pro-oxidants (oxidative damage) generated during metabolic processes, and the antioxidant barrier, a series of compounds that inhibits the detrimental oxidation of biological macromolecules. When this balance is skewed towards pro-oxidants, a state of oxidative stress occurs that might result in early ageing and advanced death. As resource allocation towards anti-oxidant protection likely comes with costs elsewhere (growth, immune function, reproduction), oxidative stress may affect fitness via different routes. Yet, the results of studies that have investigated fitness consequences of oxidative status are rather inconclusive.

Here we investigate how oxidative damage and antioxidant capacity are linked with survival and reproductive output in a wild population of Seychelles warblers (Acrocephalus sechellensis) on Cousin Island, Seychelles. We found that higher antioxidant capacity resulted in a lower probability of surviving until the next year. This matched the results of an extensive study across North-American bird species, which emphasized the importance of the pace of life: “live fast, die young” versus “live slow, die old”. The tropical Seychelles warbler falls within the second group, with basal antioxidant levels likely to be low due to their constant environment, and elevated levels that may only directly respond to higher levels of pro-oxidants produced in challenging situations. These antioxidant elevations may be traded off with reduced resource allocation into other traits, e.g., immunocompetence, thereby increasing short-term mortality.

Unlike for survival, there was no significant association between oxidative parameters and reproductive output. Individuals may successfully manage to counteract oxidative challenges so that their reproductive output is not impaired, but at the expense of lowered survival.

Care should be taken while interpreting our non-experimental results, but as it is challenging to collect physiological data in a free-living species and combine these with long-term fitness information, our study provides a valuable contribution to the attempt to better understand the role of the oxidative balance in shaping life-history trade-offs.

Image caption: Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Earlier snowmelt did not change root growth in two different subarctic plant communities

Gesche Blume-Werry, Roland Jansson, Ann Milbau  Close-up of a fine root, picture taken with a minirhizotron camera. Picture by Gesche Blume-Werry

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When snow melts earlier, plants often respond by advancing the time of leaf-out and flowering. This change can affect the interaction between plants and their pollinators and thus plant reproduction, but it also affects larger-scale ecosystem processes such as water, carbon and nutrient cycles. For example, when plants have leaves and are actively growing, they take carbon dioxide out of the air and store carbon in their tissues. Plant roots are key players in these ecosystem processes because plants use them to take up water and nutrients, and because they are a substantial part of both plant biomass and production they are also important for carbon storage. However, as they are hidden in the soil they are more difficult to measure and the role of an earlier snowmelt on timing of plant processes belowground has never been assessed.

We experimentally advanced snowmelt (with black cloth on the snow surface) in two very different plant communities and measured timing of leaf-out and flowering as well as timing of root growth. To measure the timing of root growth we used minirhizotrons, which are non-destructive in-situ measurements of fine root growth that utilize transparent tubes permanently buried in the soil and a camera system to take recurrent pictures of roots.

Our results show that earlier snowmelt increased soil temperatures and advanced leaf-out and flowering of plants, as we expected from previous studies. However, timing and amounts of root growth were unaffected in both plant communities, even though we effectively manipulated those factors that have previously been suggested as important drivers of root growth. Importantly, our findings show that aboveground plant responses cannot be directly translated belowground, and suggest that root growth starts early in spring regardless of temperature or snowmelt conditions.

Image caption: Close-up of a fine root, picture taken with a minirhizotron camera. Picture by Gesche Blume-Werry.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Do different beetle trophic groups recover after logging the same way?

Nicholas M. Fountain-Jones, Gregory J. Jordan, Christopher Burridge, Timothy J. Wardlaw, Thomas P. Baker, Lynette Forster, Morgana Petersfield and Susan C. BakerImage provided by authors.

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Beetles are not only the most species rich group of animals, but are also very diverse in function, ranging from predators and parasites to herbivores and decomposers breaking down plant material. In forest litter, beetle predators and decomposers often occupy the same patch of habitat, but how each community’s functional traits (traits of a species that can be linked to their ecological roles) respond and recover after disturbance is poorly known. Understanding to what extent functional traits of co-occuring trophic groups are constrained by evolutionary relationships (i.e., do beetles with long antennae have long antennae because their ancestors did?) can provide insights into the mechanisms of how communities assemble and recover.

We compared the functional traits and phylogenetic data (relatedness) for 133 beetle species (60 predators and 73 decomposers) from forest sites ~7 years, ~27 years and ~45 years after logging, and in neighbouring mature forest plots. We found that functional trait composition of predator communities had recovered to mature forest values after ~45 years, and this was before the communities contained even most of the species characteristic of mature forest. In contrast, for decomposers, neither species nor functional traits had recovered to mature forest values by this time. Not only were the patterns of recovery different between the trophic groups, the traits that responded to forest age, and the extent to which these traits were constrained by evolution, varied as well. For decomposers, for example, beetles were on average darker in color in ~45 year-old forest than in ~7 year-old forests, yet this trait did not differ for predators. Predator traits were also more constrained by evolutionary history compared to the decomposers. This study demonstrates that recovery patterns after logging can vary with trophic group even for the same group of animals. Furthermore, incoporating functional trait and phylogenetic data can help better understand the mechanisms underpinning these complex but diverse communities.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Sugar storage is prioritized over growth in pine trees at a dry site and explains auto-correlation in tree-ring width

Georg von Arx, Alberto Arzac, Patrick Fonti, David Frank, Roman Zweifel, Andreas Rigling, Lucia Galiano, Arthur Gessler, José Miguel OlanoThe stem sapwood, visible here as the translucent part of a wood core, is an important storage container for carbohydrates. The background shows the experimental forest stand used in this study. Photo credit: Georg von Arx.

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Carbohydrate reserves play a crucial role in tree resistance and resilience to drought. Ample reserves may buffer temporary periods when plants reduce or stop carbon uptake to prevent excessive water loss during photosynthesis. But prolonged drought might deplete carbohydrate reserves. In addition, the allocation of absorbed carbon to carbohydrate reserves competes with growth. This poses interesting questions about carbon allocation priority during periods of limited carbon uptake. For example, the availability of older carbohydrate reserves to support future growth would alleviate trade-offs between carbohydrate reserves and growth. Larger carbohydrate reserves may require larger storage capacity, which in mature conifer trees is to a large part provided by storage cells (ray parenchyma) in the stem sapwood. However, a sound understanding of how carbohydrate reserves, parenchyma abundance and growth rates are interrelated, and how they respond to changing water availability, is still missing.

In this study, we investigated these questions using 40 mature Scots pine (Pinus sylvestris L.) trees from a 10-year irrigation experiment conducted at a dry site in Switzerland. From each tree, we extracted several wood cores from bark to pith and quantified carbohydrate reserves, parenchyma abundance and ring width along radial sapwood segments. Results show that parenchyma abundance varied more than twofold among trees, but only very little from year to year within trees. In addition, parenchyma abundance slightly increased in irrigated trees, with a lag of several years, but was unrelated to the amount of carbohydrate reserves. This means we did not find evidence for parenchyma abundance limiting carbohydrate storage. While wider tree rings contained a lower concentration of stored carbohydrates, they still contained a larger absolute amount of carbohydrate reserves. We also found that rings with more carbohydrate reserves were usually followed by a wider ring.

Our results indicate a prioritization of carbon allocation to storage instead of ring growth, which we interpret as a mechanism to ensure long-term survival. In addition, the absolute amount of carbohydrate reserves proved to be a cause of the auto-correlation in tree-ring growth from one year to the next.

Image caption: The stem sapwood, visible here as the translucent part of a wood core, is an important storage container for carbohydrates. The background shows the experimental forest stand used in this study. Photo credit: Georg von Arx.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Drought effects on multispecies pinewoods spreading upwards in Mediterranean mountains

Tatiana A. Shestakova, J. Julio Camarero, Juan P. Ferrio, Anastasia A. Knorre, Emilia Gutiérrez and Jordi Voltas High-elevation mixed pine stand in the Gúdar mountain range composed of Pinus sylvestris and Pinus uncinata. Photo credit: Anastasia A. Knorre.

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Whereas tree growth is primarily constrained by water availability in Mediterranean lowlands, Mediterranean mountain forests are subjected to varying degrees of water stress depending mainly on their position along altitudinal gradients. Unravelling physiological responses along such gradients provides clues to how forests will react to emerging combinations of temperature and precipitation under climate warming. Particularly the characterisation of long-term reactions of coexisting tree species is especially relevant to contextualise the impacts of ongoing climate change in complex ecosystems.

This study investigates the extent of regionally coherent tree responses to an intensified warming-induced drought stress as imprinted in wood rings. We hypothesised that increasing drought stress has homogenized responses to climate among five pine species over the last 60 years, as drought effects have spread from low to high elevations along an altitudinal gradient (up to 2,020 m) in eastern Spain. We predicted a consistent reliance of pine performance on water conservation strategies at low elevations throughout the study period. Conversely, we expected a weaker dependence on water saving mechanisms higher up the gradient, but a gradual convergence at low- and mid-elevations (from 1,100 to 1,600 m) as sensitivity to drought became more limiting for photosynthesis.

We observed enhanced growth synchrony (that is, more coherent changes in ring-width patterns) between low- and mid-elevation pinewoods, a phenomenon attributable to increasingly negative annual water balances from the 1950s. Our results also indicated that nowadays drought effects on pine performance start earlier in the growing season (early spring) at low and mid elevations (driest sites). Particularly, we observed an increasing dependence of radial growth on needle control of water losses spreading upwards in mountain forests, hence resembling lowland forests. All together, these findings demonstrate that drought is gaining relevance over stand effects (e.g., topography, nutrient availability) as the main factor controlling multispecies tree physiology and productivity and is likely to increase pines’ sensitivity to competition. Our observations constitute non-visible early warning signals of forest vulnerability to climate change traceable back in time through the analysis of tree rings.

Image caption: : High-elevation mixed pine stand in the Gúdar mountain range composed of Pinus sylvestris and Pinus uncinata. Photo credit: Anastasia A. Knorre.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Impacts of future UK rainfall patterns can move through the food chain

Ruth N. Wade, Alison J. Karley, Scott N. Johnson and Sue E. HartleyWireworm foraging for roots. Photograph taken by Ruth Wade.

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Climate change is predicted to cause more variable rainfall in the UK, including increased incidence of extreme drought and heavy rainfall events, and overall reductions in summer precipitation of up to 40% by 2080. These altered rainfall patterns will mean periods of stress and recovery for plants, with dry days followed by heavy rainfall events potentially impacting plant growth. Herbivores and their predators will also be affected by changes in rainfall through altered availability and quality of their food. Interactions between species in a food chain underpin the functioning of an ecosystem; therefore, understanding the impacts of future changes in precipitation on such interactions is important for food security, pest management and for constructing more accurate predictions of global change impacts. Despite the importance of this knowledge, little research has been conducted to investigate whether changes in plant growth arising from predicted rainfall patterns affect interactions between above- and below-ground herbivores and insect predators.

We conducted two experiments, one in controlled conditions and one outside under rainshelters, to test the effect of a 40% reduction in water supply, at two different watering frequencies, on the interactions between root and shoot feeding herbivores and their natural enemies. A continuous drought regime reduced plant growth significantly whereas plant growth was unaffected under a drought regime where water was delivered by infrequent ‘ deluge’ events. However drought/deluge watering events changed the chemical composition of the plant, which benefitted the growth of shoot-feeding aphids and their predator, the invasive harlequin ladybird. Furthermore the drought/deluge watering regime reduced the negative effects of root-feeding wireworms on plant growth and aphid numbers above-ground.

Therefore, changes in the quantity and frequency of rainfall events had a significant impact on insect herbivores above- and below- ground and these effects transferred up the food chain to insect predators, indicating consequences of altered rainfall patterns for crop production, control of agricultural pests and success of invasive insect species.

Image caption: Wireworm foraging for roots. Photograph taken by Ruth Wade.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Fish Contests and Community Structure

Kai C. Paijmans and Marian Y.L. WongField work on an intertidal rocky shore in SE Australia (Photo Credit – Matt Rees).

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Contests are a method by which animals resolve conflict over access to resources such as food, shelter and mates. Contest theory is a complex set of models which explain the mechanisms, dynamics and outcomes of animal contests. Because competition for limiting resources is an established mechanism by which species coexist and biodiversity is maintained, contest theory has potentially important applications in understanding species coexistence and biodiversity maintenance within ecosystems. We applied contest theory to investigate the link between contest dynamics and species coexistence using two intertidal rockpool fishes - Bathygobius cocosensis (the cocos frill goby) and Lepidoblennius haplodactylus (the eastern jumping blenny). Firstly, we assessed the abundance and distribution of the two species on intertidal rocky shores of South East Australia. Secondly, we conducted interspecific contest experiments between pairs of B. cocosensis a nd L. haplodactylu s to assess the competitive dominance of the species. Then finally, to relate these results to community structure, we quantified the rockpool fidelity (the amount of time fish spend in a “home” pool) of each species on the rocky shore. We found that B. cocosensis and L. haplodactylus appeared to avoid each other in the field and that B. cocosensis displayed higher rockpool fidelity than L. haplodactylus. Contest experiments revealed that B. cocosensis was competitively superior and highly aggressive relative to L. haplodactylus. Furthermore, the microhabitat preference of L. haplodactylus changed in the presence of B. cocosensis. In light of these findings we propose that, B. cocosensis is the superior competitor, but coexistence of both species is facilitated by low-cost contest resolution strategies, plasticity in microhabitat preference and interspecific variation in home range sizes. Overall, this study highlights the applicability of contest theory for investigations of community scale ecology, community dynamics and biodiversity maintenance across a wide range of ecological systems.

Image caption: Field work on an intertidal rocky shore in SE Australia (Photo Credit – Matt Rees).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Mowing exacerbates the loss of ecosystem stability under nitrogen enrichment in a temperate grassland

Yunhai Zhang, Michel Loreau, Nianpeng He, Guangming Zhang, Xingguo Han Image provided by authors.

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The increasing availability of biologically active nitrogen (N) caused by fertilizers and atmospheric deposition has resulted in biodiversity loss in terrestrial ecosystems. Mowing (or biomass removal) is a crucial management strategy for restoring plant diversity in the face of increased N deposition/fertilization. Both N enrichment and mowing affect biodiversity and ecosystem stability, i.e., the inverse of the coefficient of temporal variability of ecosystem net primary productivity; however, it is unclear how mowing affects ecosystem stability with increasing N enrichment.

We conducted a field study (also see the photograph) with nine rates of N application (i.e., 0, 1, 2, 3, 5, 10, 15, 20, and 50 g N·m–2·yr–1) that were applied with two frequencies (two times per year versus monthly) and two mowing regimes (unmown versus mown) to investigate their effects on species richness (number of plant species m–2), species asynchrony (the asynchrony of the species response to environmental fluctuations), ecosystem stability, and the diversity–stability relationship in a temperate grassland in northern China.

During the studied period (2011–2013), the frequency of N addition had no significant effects on species richness, species asynchrony, ecosystem stability, or the relationship between species richness and ecosystem stability. But increasing the rate of N addition significantly decreased species richness, species asynchrony, and ecosystem stability. Mowing exacerbated the negative effects of N addition on ecosystem stability, but did not affect the positive relationship between species richness and ecosystem stability. Mowing increased mean ecosystem primary productivity, species richness, and species synchrony under N enrichment. Thus, infrequent mowing had positive impacts on species richness and aboveground net primary productivity, but had negative effects on ecosystem stability via a reduction in species asynchrony under N enrichment.

Our findings indicate that N enrichment can increase ecosystem productivity, but reduces species richness and ecosystem stability, and infrequent mowing can buffer the negative effects of N enrichment on biodiversity to some extent. Infrequent mowing with N enrichment may improve ecosystem productivity but reduces ecosystem stability over time.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

Special Feature: The Ecology of De-Extinction

Conservation genetic implications of de-extinction

Tammy E. Steeves, Jeff A. Johnson and Marie L. HaleImage provided by authors.

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The idea of resurrecting phenotypic traits once possessed by extinct species to create extant functional proxies to restore ecological function (de-extinction sensu stricto; IUCN/SSC 2016) is captivating the imagination of scientists and non-scientists alike. In our view, conservation geneticists have yet to adequately weigh in, despite the obvious “genetic issues” raised by de-extinction. In our perspective, we use conservation genetic principles to show that to increase the probability of long-term persistence for any functional proxy populations successfully translocated to the wild, creating and maintainng evolutionary potential is essential.

The ability to evolve in response to a changing environment (evolutionary potential) requires genetic diversity at loci for functionally important traits, and the level of genetic diversity in a population depends to a great extent on the effective population size, as small populations lose diversity quickly through genetic drift. In our perspective, we consider the stages of the de-extinction process likely to result in a genetic bottleneck and thus the stages where loss of genetic diversity needs to be considered and mitigated. These stages include: ‘pre-extinction’, due to small population size prior to extinction; ‘resurrection’, due to the small number of museum specimens usually available to provide material for resurrection; ‘captivity’, due to limitations on the number of resurrected individuals that can be kept in captivity; and ‘translocation’, due to limitations on the number of captive individuals that can be released and managed/monitored in wild populations.

To realise the ecological benefit of de-extinction, self-sustaining (genetically viable) populations of functional proxies are required. To be genetically viable, populations need to be sufficiently large and genetically diverse (i.e. have relatively high evolutionary potential). Beyond embedding the genetics of small populations into the scientific discourse on de-extinction, our intent is to spark robust dialogue in the peer-reviewed literature that critically evaluates the inherent complexities of creating and maintaining biodiversity in a changing world.

 

Niche variation between fish communities as reconstructed from stable isotopes in two ecologically different Ethiopian Rift Valley lakes

Pieter Lemmens, Fassil E. Teffera, Maarten Wynants, Lynn Govaert, Jozef Deckers, Hans Bauer, Feleke Woldeyes, Luc Brendonck, Steven Bouillon and Luc De MeesterSatellite image showing Lake Abaya and Lake Chamo (left and right respectively) (Landsat-8 image, 2016).

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The concept of species niches – the role they play in the ecosystem - helps us to understand the structure and dynamics of biotic communities and food webs. An increasing number of studies indicates that variation in niches among individuals of the same species is an important determinant of food web characteristics.

In the present study, we compare the feeding niche of the fish community in two iconic Ethiopian Rift Valley lakes, Lake Abaya and Lake Chamo. These lakes differ strongly in ecology. Lake Abaya is a turbid lake with low primary production, whereas Lake Chamo is a clear-water lake with high primary production. Using stable isotopes of carbon and nitrogen, which allow us to determine what fish are eating, we investigate how far differences in fish feeding ecology between the two lakes are mediated by changes in species composition or rather by variation in feeding niche between individuals of the same species.

While we do not observe significant differences in fish community composition between the lakes, our results show that the feeding niche of the fish community in Lake Abaya is larger and more diversified compared to that in Lake Chamo. Fishes in Lake Abaya feed mainly on less nutritious sediment organic material, while zooplankton is a major food source for fish in Chamo. We show that observed differences in feeding ecology result from differences between lakes in the niches of individuals of the same species rather than from differences in fish species composition.

We argue that the observed differences in fish feeding ecology between both lakes likely result from the strong difference in primary production between the lakes. Fishes in Lake Chamo rely mainly on local primary production by feeding on zooplankton, whereas fishes in Lake Abaya seem to be forced towards consumption of alternative sources due to the much reduced primary production. Our study highlights the importance of niche variation among individuals of the same species for the feeding ecology of fish communities inhabiting two large Ethiopian Rift Valley lakes with distinct environmental conditions.

Image caption: Satellite image showing Lake Abaya and Lake Chamo (left and right respectively) (Landsat-8 image, 2016).
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Standing stage accelerated litter decomposition and soil organic carbon formation in semi-arid region

Jing Wang, Lingli Liu, Xin Wang, Sen Yang, Beibei Zhang, Ping Li, Chunlian Qiao, Meifeng Deng, Weixing LiuLandacape. Image provided by authors..

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The decomposition of dead plant material, such as leaf litter, plays an important role in global carbon and nutrient cycles. Litter in semi-arid ecosystems usually undergoes a prolonged standing dead phase after senescence. Although standing litter constitutes a large fraction of aboveground litter in arid and semi-arid ecosystems, our knowledge of litter decomposition in grasslands is almost exclusively derived from studies on litter that has fallen on the soil surface. We know little about the ways in which abiotic and microbial processes affect standing litter decomposition.

Here, we conducted a 26-month in situ decomposition experiment in a semi-arid grassland in Inner Mongolia, China and a 192-day laboratory incubation experiment. We want to know the potential mechanisms governing the decomposition of standing litter. We also interested in whether the standing stage will affect subsequent litter decomposition and soil organic carbon formation after falling to the soil surface.

We found that standing litter decomposed significantly faster than soil surface litter. This was because standing litter experienced higher nighttime humidity than surface litter, which increased litter moisture content and stimulated microbial activity. Standing litter also has higher dissolved organic carbon concentration. The higher dissolved organic carbon concentration, combined with the greater night-time moisture content increased microbial decomposition of standing litter. Moreover, the standing phase conditioned the litter and increased its microbial biodegradability, leading to a more rapid decomposition after the litter fell to the soil surface and increasing the efficiency with which the litter formed soil organic carbon.

We conclude that the long-neglected standing phase greatly determines litter decomposition and soil carbon storage in semi-arid grasslands. Accounting for standing litter decomposition is critical for accurately simulating carbon turnover in these regions.

Image caption: Landacape. Image provided by authors..
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Fear makes you fat, but not too fat to fly

Benjamin T. Walters, Tin Nok Natalie Cheng, Justin Doyle, Chistopher G. Guglielmo, Michael Clinchy and Liana Y. Zanette One of the large outdoor aviaries in which the experiment was conducted.  The speaker boxes through which predator or non-predator sounds were broadcast are evident on the struts near the ceiling on the right-hand side.  The apparatuses (2 in total) we used to measure the angle and speed of escape at take-off are evident on the ground.  The study species (brown-headed cowbird) is evident in the far corner on the left.

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Escaping from a predator is a matter of ongoing life or immediate death. While escape ability is clearly imperative for survival, the variables that impair or improve it are not well understood. Escape ability is frequently assumed to be dependent on body mass, whereby getting fat can compromise escape while slimming down enhances it. Consequently, prey living with a lot of predators around may be expected to strategically alter their body mass to enhance escape. This “mass-dependent predation risk hypothesis” makes good theoretical sense, especially for birds that fly to escape from a predator attack, requiring them to lift their entire body mass off the ground. If light birds do have more lift than fat birds do, then light birds should be superior escape artists.

We tricked birds living in semi-natural conditions into thinking that predators were around using sounds and taxidermic models to test whether scared prey alter both body mass and escape ability, and whether body mass has any effect on flying ability. We found that scared birds actually gained mass by packing on fat, which they lost again when exposed to non-predator cues. Although scared birds were heavier, this did not interfere with their ability to fly, and indeed, scared birds enhanced their escape prospects by taking off at steeper angles, relying on evasion rather than brute force. This experiment, and then a second one we conducted in the lab, both confirmed that no amount of mass loss makes any bird a better flier, and only individuals that became abnormally fat flew worse.

Our experiments reveal that predators cause prey to alter escape behaviour and actually gain weight but that the magnitude of weight gain is strategically orchestrated to ensure that flying ability is not compromised. Whenever a predator is perceived nearby, fatter prey can hide in safety and forgo looking for dinner to avoid becoming dinner. While fat gain is thus beneficial to frightened prey, the amount of fat gained is tempered so as not to tamper with flight, presumably because flight is just too important for predator escape.

Image caption: One of the large outdoor aviaries in which the experiment was conducted. The speaker boxes through which predator or non-predator sounds were broadcast are evident on the struts near the ceiling on the right-hand side. The apparatuses (2 in total) we used to measure the angle and speed of escape at take-off are evident on the ground. The study species (brown-headed cowbird) is evident in the far corner on the left.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Coexisting tree species share similar characteristics

Mickaël Chauvet, Georges Kunstler, Jacques Roy, Xavier MorinImage provided by authors.

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Most forests in Central Europe are composed of many tree species. How do so many species co-exist in the long-term? Using a simplified sequential view of species assembly, the abiotic conditions first select a set of species that can colonize a site, depending on their tolerances to local environmental constraints. Then, competition for light between established trees determines species that can coexist locally. In forest communities, small-scale disturbances like deaths of large trees create gaps in the canopy. Such gaps locally create new light conditions, and some tree species called pioneers can efficiently colonize these gaps immediately after their formation because of their ability to grow quickly in full light. Then, as the forest becomes darker because trees grow, some other tree species called late-successional species slowly colonize the gaps because they are shade-tolerant and are thus better competitors than pioneers. Forest communities are thus dynamic systems experiencing gaps over time. At the whole forest scale, however, it is not clear whether these gap dynamics lead to the coexistence of species with different characteristics, i.e. a mosaic of patches of various ages promoting the coexistence of both pioneers and late-successional species, or whether late-successional species mostly dominate forest communities because they are the best competitors on the long-term.

Here we used a model simulating gap dynamics in Central European forests to explore the relative importance of abiotic conditions and competition in determining species diversity, and also to test how gap dynamics drive tree species coexistence.

We found that abiotic conditions play an important role in structuring tree communities, especially in harsh conditions where it strongly reduces the number of species that can potentially establish in a particular site. Competition plays a crucial role in forest community structure both in favourable and harsh conditions, although its effects were more pronounced in favourable sites. Finally, despite gap dynamics, forest communities are mostly dominated by late-successional species that exclude pioneers when both type of species compete for light in the long-term. Finally, our model-based approach offers an alternative way to study the processes leading to tree species coexistence in forests, and complements empirical and experimental approaches.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Species but not genotype diversity strongly impacts the establishment of rare colonisers

Christian Schöb, Sara Hortal, Alison J. Karley, Luna Morcillo, Adrian C. Newton, Robin J. Pakeman, Jeff R. Powell, Ian C. Anderson and Rob W. BrookerBarley weed mixture experiment.

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Environmental factors such as climate or land use are known to affect biodiversity. However, do we know how the existing diversity of an ecosystem affects the diversity of newly arriving organisms? Depending on the theory at hand we can argue that this effect should be positive or negative. On the one hand, we could expect that a more diverse existing community, with a range of species that each use resources differently, would deplete the resources more effectively and leave less available space for newly arriving species. Based on this theory, the effect of the species diversity of the existing community on the diversity of newly arriving species would be negative. On the other hand, we could expect that a more diverse existing community, with a range of species each having different effects on their surroundings, would create a more diverse environment that may in turn support more arriving species. Based on this theory, the diversity effect of the existing community on the diversity of newly arriving species would therefore be positive.

In this study, we tackled this issue by creating plant communities of different levels of genetic and species diversity. We created communities ranging from a single cultivar of barley (our most uniform community) up to communities consisting of five different cultivars of barley and five different weed species (our most diverse community) and assessed their impact on newly arriving species, i.e. species we added into these communities. We found that while species diversity of the existing community had a negative impact on the diversity of new arrivals, barley genetic diversity had no significant effect. Interestingly, the species diversity effect of the existing community was most negative for the rarest arriving species, while the most common arriving species were only weakly affected.

The negative “diversity-on-diversity” effect that we found suggests that diversification of crop fields could be a natural measure to suppress weeds and reduce herbicide usage. In contrast, the differential responses of the newly arriving species to the diversity of the existing communities could actually explain their commonness and rarity in nature and provide hints for the conservation of rare species.

Image caption: Barley weed mixture experiment.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

New evidence for regulation of seasonal breeding in mammals by the reproductive hormone kisspeptin

Allison M. Bailey, Sandra J. Legan, and Gregory E. Demas  Siberian hamster long day length (bottom) and short day length (top) reproductive morphs. Photographer: Aaron Jasnow

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Many parts of the world feature extreme changes in climate during a year, which result in seasonal fluctuations of many factors that affect animals’ survival (e.g., temperature, rainfall, food availability). Animals living in these areas often limit breeding to seasons that are most favorable for their offspring to survive. For example, Siberian hamsters reproduce during the summer, when days are long and food is plentiful. In the short days of winter, these hamsters go through a transition termed gonadal regression, in which their gonads shrivel and become incapable of supporting reproduction. Gonadal regression is crucial for successful survival and reproduction in many seasonally breeding rodents and birds, but we do not yet know exactly how it is controlled; that is, we do not know the specific hormonal mechanisms involved or precisely what changes in the environment are capable of triggering it.

Kisspeptin is a hormone found in the brain that stimulates reproduction (it triggers the onset of puberty in mammals, including humans) and may play a role in regulating seasonal processes like gonadal regression. In this study, we investigated whether an outside source of kisspeptin could support male Siberian hamster reproductive function while the hamsters were exposed to environments signaling the onset of winter, which would normally trigger gonadal regression. We provided hamsters with injections of kisspeptin while they were exposed to combinations of short, winter-like day lengths or intermediate, fall-like day lengths with either unlimited food or a mild restriction of food availability (90% of their natural intake was provided).

We found that kisspeptin injections prevented the full process of gonadal regression in male hamsters exposed to short day lengths regardless of food availability, and in hamsters exposed to intermediate day lengths combined with food restriction. Based on hormonal data collected, we also think kisspeptin might act directly on the gonads to control regression, rather than exclusively in the brain, which suggests new avenues for research.

These findings expand our understanding of how animals successfully survive and reproduce in changing environments. Specifically, they provide evidence that kisspeptin is indeed an important hormonal regulator of seasonal reproductive function in mammals.

Image caption: Siberian hamster long day length (bottom) and short day length (top) reproductive morphs. Photographer: Aaron Jasnow.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Trait-matching and mass determine the response of herbivore communities to land use intensification

Gaëtane Le Provost, Nicolas Gross, Luca Börger, Hélène Deraison, Marilyn Roncoroni123, Isabelle Badenhausser Grasshopper in a grassland field. Photo credit: Gaëtane Le Provost

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Understanding how different organisms interact is essential to understand what drives the structure of ecological communities and how they may be affected by environmental change. One important type of interaction is a “trophic interaction” – who eats whom – and for many species the morphological attributes that determine these interactions (“trait-matching”) have been identified. For instance, we know that bird beak size is adapted to the size of the seeds they eat, or that pollinators with long tongues visit plants with deeper flowers. However, how such trait-matching between animals and their resources explains the structure of natural communities has been barely explored. This question might be particularly relevant for agricultural areas, which are subject to drastic changes globally (e.g. more intensive production methods), as the diversity of traits that help secure key resources (known as resource-acquisition traits) may inform us about the diversity of resources present in the landscape, and whether diverse animal communities can be maintained in agricultural landscapes.

In this paper, we quantified the relative contribution of trait-matching between plants and herbivores and land use intensification, operating at local and landscape scales, on the structure of ecological communities. To do so, we compiled a large dataset on the abundance and morphological/chemical attributes of plant and grasshopper species from 204 grasslands, situated in an intensively managed agricultural landscape. We considered two key functional traits of grasshopper species: (i) incisor strength, a resource-acquisition trait which strongly matches grasshopper feeding preferences; and (ii) body size, which correlates with mobility traits and may determine grasshopper dispersal abilities in fragmented landscapes. We found that land use intensification decreased the diversity of grasshopper resource-acquisition traits and tended to select for large and mobile grasshoppers. Trait-matching between plants and grasshoppers was an important driver explaining the abundance and diversity of grasshopper communities. Diverse plant communities in old grasslands support diverse grasshopper communities, characterized by contrasting feeding preferences. Importantly, our study suggests that diversity of resource-acquisition traits in grasshoppers was also influenced by the presence of diverse habitats in the surrounding landscape. Thus, in agricultural landscapes, diverse and stable habitats are required to maintain a diversity of resources and sustain functionally diverse animal communities.

Image caption: Grasshopper in a grassland field. Photo credit: Gaëtane Le Provost.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Unlocked function of snow crystal-like flowers of Bishop’s caps

Koki R. Katsuhara, Shumpei Kitamura and Atushi Ushimaru  Fungus gnats grasped the petals of Mitella pauciflora flower. Photo provided by S. Kitamura.

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The tremendous diversity of flowers, especially their petal diversity, has long fascinated people all over the world. While petal diversity has been mainly discussed in relation to visual attraction of animal pollinators, it is difficult to explain all petal diversity solely with this function. Petals have been also hypothesized to serve as landing sites for pollinators, but only a handful of studies have examined this topic. This is because most plants have showy petals and their function to provide their pollinators with landing sites cannot be easily separated from their function to visually attract pollinators.

Here, we examined the landing-site function of petals using the scent-attracting flowers of Bishop’s cap (Mitella pauciflora), which is pollinated by fungus gnats. Many fungus-gnat pollinated flowers attract insects with floral scents and often have dull-coloured and tiny petals that are unlikely to contribute to their own visual attraction. Thus, fungus-gnat flowers are ideal subjects to independently test the landing-site function. Bishop’s cap flowers look like snow crystals and have greenish pinnately-branched petals. We experimentally removed the petals to record changes in pollinator behaviour by combining time-lapse photography and direct observation. Also, we examined female and male reproductive success in terms of fruit set and pollen removal by fungus gnats, respectively, to test the effect of inconspicuous petals on the plant’s fitness.

We found that petal removal substantially reduced the fungus-gnats’ post-approach landings but did not influence the approach frequency. The plant’s fruit set and pollen removal by fungus gnats also decreased with petal removal, indicating that the petals of Bishop’s cap enhance the plant’s fitness via offering the tiny insects landing sites but not via attracting them visually. The findings firstly and quantitatively demonstrate the function of inconspicuous, elaborate petals of flowering plants. Isolating diverse petal roles is a challenging task, but will enhance our understanding of petal diversity in flowering plants.

Image caption: Fungus gnats grasped the petals of Mitella pauciflora flower. Photo provided by S. Kitamura..
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Long-term time series of legume cycles in a semi-natural montane grassland: evidence for nitrogen-driven grass dynamics?

Tomáš Herben, Hana Mayerová, Hana Skálová, Věra Hadincová , Sylvie Pecháčková, František Krahulec Mountain grassland. Image provided by authors

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The extraordinary species richness of mountain grasslands often hides less obvious dynamics of individual species, which may appear and disappear over time. One of the conspicuous examples is cycles of legumes (such as clover). Importantly, legumes, in contrast to most other grassland species, can obtain nitrogen directly from the atmosphere and thus such shifts in their abundance can have profound effects on availability of this essential element in the whole system. Although there are number of indirect observations that support the existence of legume cycles, they have never been shown using sufficiently long term data of abundance and nitrogen availability. We were fortunate to have long term observations (~30 years) of legume abundance in a mountain grassland, together with data on soil nitrogen content over the same observation period. Using such unique data, we were able to show that legumes indeed show marked cycles (lasting about 9 years), but also that these cycles are linked to cycles of nitrogen availability and cycles of biomass of grasses. Peaks of legumes, nitrogen and grasses are shifted against each other: a peak of nitrogen availability follows a peak of legumes and is followed by a peak of grasses. This is easily explained by the fact that legumes provide nitrogen that the grasses depend on. The legumes begin to increase when nitrogen availability in the system is low and provide the system with available nitrogen which subsequently leads to increase of grasses. We show that the decline of legumes is not due to competition by grasses, but is driven by unknown other agents (pathogens, soil organisms etc.). After the nitrogen is used up, the grasses begin to decline due to nutrient starvation. Legumes are thus the key driver of nitrogen dynamics in such nutrient-poor semi-natural grasslands. While grasses benefit from the nutrient enrichment due to legumes, they are rather a passive element in the process. Such dynamic processes are important in maintenance of species richness: while individual species come and go, the overall long-term richness of such meadows is maintained.

Image caption: Mountain grassland. Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Slow development as a cost of long life

Martin I. Lind, Hwei-yen Chen, Sara Meurling, Ana Cristina Guevara Gil, Hanne Carlsson, Martyna K. Zwoinska, Johan Andersson, Tuuli Larva and Alexei A. MaklakovPhotograph provided by authors.

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Long life is not for free; instead evolutionary theory predicts that investment in early life reduces lifespan, since resources are taken away from maintenance of the body, resulting in short life and reduced resistance to stressful conditions. Commonly, high reproduction is associated with short life, but in many cases animals can have high reproduction and still have a long life. Can long life then be for free after all?

Reproduction is not the only costly trait; animals also have to develop from an egg cell to a fully developed sexually mature animal, and they also have to grow larger. Previous studies have shown that rapid growth is also associated with short lifespan. But what about development? To develop new cells and tissues is fundamentally different from growing in size, but these processes are hard to separate. The millimeter-long soil nematode worm Caenorhabditis remanei offers an opportunity to differentiate between development and growth, since cell division and therefore development stops at sexual maturation, while most of the growth remains.

We studied this using evolution in the lab. First we selected worms in environments with different stress levels. Worms from stressful environments evolved a longer lifespan, at the cost of slow development. We then performed another evolution experiment, where we selected worms with either short or long development time. We found that worms that had evolved long development were also long-lived and stress resistant, while they still had the same reproduction as the fast developing worms, and no consistent pattern was found for growth. Thus, our results suggest that fast development is costly in terms of lifespan and stress resistance.

Why do animals then develop fast? Many animals live in temporary environments, for example a seasonal environment where development has to be finished before winter comes or the pond dries out. The nematode in this research naturally lives on decomposing fruit, an environment that is short-lived and where fast development would be advantageous. Our results therefore suggest that organisms living in temporary environments, which have repeatedly been shown to evolve fast development, may pay the price of a short lifespan.

Image caption: Photograph provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Resistance of plant–plant networks to biodiversity loss and secondary extinctions following simulated environmental changes

Gianalberto Losapio & Christian SchöbSampling plot of plant species in the Sierra Nevada Mountains (Spain) at 2725 m a.s.l. The grass Festuca indigesta Boiss. (Poaceae) is supporting other plant species to survival in this stressful environment. © Christian Schöb.

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In Mediterranean alpine ecosystems, harsh conditions make plants’ lives difficult: drought, low temperature, poor soil and strong winds are some of the problems plants have to cope with to survive and reproduce. Two decades ago, ecologists started to report that plants can cooperate with neighbouring plants to survive in such a harsh environment. Since then, hundreds of studies were subsequently conducted, but few of these described the network of interacting plant species, despite our knowledge that natural plant communities are organized in such interaction networks. Thus, it remains unclear whether such plant interaction networks differ in their resistance against different environmental changes. Here we assessed the susceptibility of a network of interacting plants to simulated increases in drought, temperature and drought, and nitrogen deposition.

We combined observational data from an alpine vegetation in the Sierra Nevada Mountains (Spain) with computer simulations to explore the probabilities of these environmental changes causing species extinctions, either due to environmental conditions becoming unsuitable or due to the loss of their microhabitat. We found that plant interaction networks’ responses, and the extinctions of species, depended on the type of environmental change. In particular, the studied plant community was most resistant against species losses when drought increased. However, it was least resistant, and experienced early and heavy species losses, when nutrient pollution increased. We further showed that the higher network resistance against increasing drought was due to drought-tolerant species that facilitated the survival of many other plant species.

This study suggests that the fate of species and communities with the on-going global environmental changes will depend on the main driver of environmental change and how this might affect the network of interacting species. Consequently, knowledge about species interaction networks in natural communities could improve our understanding of how ecosystems will respond to global changes, which in turn may help to improve current conservation and restoration practices.

Image caption: Sampling plot of plant species in the Sierra Nevada Mountains (Spain) at 2725 m a.s.l. The grass Festuca indigesta Boiss. (Poaceae) is supporting other plant species to survival in this stressful environment. © Christian Schöb.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

How diverse fish species coexist in the Amazon Basin

Daniel B. Fitzgerald, Kirk O. Winemiller, Mark H. Sabaj Pérez, Leandro M. SousaHypancistrus zebra, known commonly as the zebra pleco, is one of numerous species that are found only in the Xingu River. Photo by: Mark H. Sabaj Pérez.

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In the Xingu River, a major tributary of the Amazon River, over one hundred fish species adapted to life in swift flowing water coexist in a series of rapids a few hundred kilometers long. How do tropical regions maintain such high levels of diversity? Part of the answer to this question lies in understanding why certain species occur together while others do not, a process known as community assembly. Recently, ecologists have studied community assembly using species’ traits, or characteristics such as the size and shape of different body parts that influence how species interact with their environment and other species. Shared habitat and resource requirements may cause species with similar traits to occur together, while competition for limiting resources may lead to co-occurring species having divergent trait values to minimize competition.

Different traits may be involved in separate aspects of species’ ecology, causing species occurring together to be similar in some traits and divergent in others. Species found in rapids worldwide tend to have similar body shapes designed to cope with high water velocities, but high diversity in the tropics increases potential competition for food resources. Therefore, we expected that species occurring together in rapids of the Xingu River would be more divergent in traits associated with feeding compared to traits related to swimming performance. To test this, we measured 45 traits related to swimming performance and feeding behavior for 37 species, and correlated each trait with species’ trophic position to estimate how strongly a trait is associated with feeding. Then, we tested if traits with stronger correlations with trophic position are more divergent among co-occurring species relative to weakly correlated traits.

We found traits with stronger associations to trophic position were more divergent among species occurring together compared to traits with weaker associations. This result demonstrates that multiple factors can influence community assembly simultaneously and that our understanding of this process may vary depending on the traits we analyze. It also suggests that traits involved in feeding behavior may play an important role in promoting the ecological differences that help maintain high levels of diversity in tropical rivers.

Image caption: Hypancistrus zebra, known commonly as the zebra pleco, is one of numerous species that are found only in the Xingu River. Photo by: Mark H. Sabaj Pérez.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

How nitrogen and plant diversity interact in decomposition of leaf litter in streams

Alan M. Tonin, Luz Boyero, Silvia Monroy, Ana Basaguren, Javier Pérez, Richard G. Pearson, Bradley J. Cardinale, José Francisco Gonçalves Jr., Jesús PozoImage provided by authors.

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Biodiversity is currently being lost at an alarming rate, and understanding the effects of such loss on how ecosystems function is a major scientific challenge. One key ecosystem process potentially affected by the loss of plant species is decomposition of leaf litter, which is crucial to carbon and nutrient cycling in terrestrial and aquatic ecosystems. Whether or not the number of plant species affects the rate at which litter is decomposed is still under debate, partly because of the complex role of different plant characteristics, and because of the influence of environmental variables. We explored the influence of two factors on the relationship between the number of plant species and decomposition rate in streams: the plants’ ability to harness bacteria that fix atmospheric nitrogen, making it available to the plant; and the concentration of dissolved inorganic nitrogen in the water, which is a key environmental factor, often enhanced by human activity. We conducted a laboratory experiment that mimicked stream conditions, in which we exposed different combinations of plant species, with or without nitrogen-fixing capacity, to organisms that decompose litter (microbes such as fungi and selected invertebrates) at natural and elevated nitrogen concentrations. We found that increasing the number of plant species increased decomposition rate, subject to the influence of microorganisms and invertebrates (the latter having stronger effects). However, the ability of plants to fix nitrogen was not important, as this ability was not related to the nitrogen concentration of litter, and probably because other litter characteristics played a role. In contrast, nitrogen concentration of the water modulated the effect of larger numbers of plant species on decomposition because it enhanced the decomposition of nitrogen-poor litter by microbes. Our findings suggest that the consequences of loss of terrestrial plant species for decomposition in streams will depend on the identity of the species that are lost or remain and on levels of nitrogenous pollution, typically associated with fertiliser run-off and animal and human waste.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Differential responses of ecosystem carbon and water processes to increased and decreased precipitation

Bingwei Zhang, Xingru Tan, Shanshan Wang, Minling Chen, Shiping Chen, Tingting Ren, Jianyang Xia, Yongfei Bai, Jianhui Huang, Xingguo Han  View of the precipitation manipulation experiment in a semiarid grassland, Inner Mongolia, China. Photo by Bingwei Zhang.

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Precipitation is one of the key determinants of productivity in almost all terrestrial ecosystems, through its effects on plant photosynthesis and respiration. Global climate change is predicted to alter precipitation with greater inter-annual fluctuation, with consequent effects on plant photosynthesis and respiration, and thus on ecosystem productivity.

Arid and semiarid ecosystems, like deserts and grasslands in rainless regions, represent the largest terrestrial biome, and are extremely sensitive to changing precipitation. Therefore, arid and semiarid ecosystems play an important role in global carbon cycling. Many manipulation experiments in these regions have found increased precipitation promoted ecosystem photosynthesis and respiration, and ultimately productivity; decreased precipitation reduced them. However, it is still inconclusive whether the influence intensities are equal between decreased and increased precipitation, for the lack of experiments combining decreased and increased precipitation treatments together. To answer this question, we conducted a 5-level precipitation manipulation experiment with both decreased and increased precipitation treatments in semiarid grasslands of Northern China during 2012-2014. Specific goals were to examine the influences of changing precipitation on gross ecosystem photosynthesis (rate of total CO2 uptake by plants), ecosystem respiration (rate of CO2 release by plants and soil microbes), net ecosystem photosynthesis (difference between gross ecosystem photosynthesis and respiration, representing net ecosystem productivity), ecosystem evapotranspiration (rate of water release from soil evaporation and plant transpiration), carbon use efficiency (ratio of net to gross ecosystem photosynthesis) and water use efficiency (ratio of gross ecosystem photosynthesis to evapotranspiration).

Our study showed that decreased precipitation reduced photosynthesis, respiration and evapotranspiration; in contrast, increased precipitation did not significantly increase those processes. That is, the effects of decreased precipitation were greater than those of increased precipitation. Soil water content was the most important factor determining changes in gross ecosystem photosynthesis, ecosystem respiration and evapotranspiration. Soil temperature caused by changing precipitation, meanwhile, explained most of the variation in net ecosystem photosynthesis and carbon and water use efficiency. The asymmetric response to changing precipitation tells us that the relative effects of decreased and increased precipitation on ecosystem processes cannot be assumed to be similar. Taking this into consideration will inevitably reduce uncertainties in simulating global carbon cycling.

Image caption: View of the precipitation manipulation experiment in a semiarid grassland, Inner Mongolia, China. Photo by Bingwei Zhang.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Temperate and tropical snails share an appetite for native and non-native temperate aquatic plants

Bart M.C. Grutters, Yvonne O.A. Roijendijk, Wilco C.E.P. Verberk, Elisabeth S. BakkerSnail eating freshwater plants. Photos provided by authors.

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The plants and animals found in our ecosystems are rapidly changing because of a warming planet and the global transport of people and goods. As a consequence, Himalayan balsam colors our river banks pink, Japanese knotweed is the bane of house owners and floating pennywort transforms waterways into buoyant lawns. Ultimately, the success of such non-native plants depends strongly on whether native herbivores feed on them. Native herbivores and non-native plants are evolutionarily novel to each other (i.e. they have not evolved adaptations to one another), which can benefit either plant or herbivore. If herbivores are maladapted to consume exotic plants, the non-native plants will grow vigorously. Alternatively, if novel plants are maladapted to native herbivores, there will be strong biotic resistance against plant invaders because herbivores will prefer them to natives. Because novelty can work both ways, it does not consistently predict the palatability of plant invaders.

We tested whether plant palatability traits (plant traits that were expected to be indicative of their palatability to snails) and the latitudinal origin of plant species would help explain the palatability of non-native plants. We fed twenty native and twenty non-native aquatic plants (some of temperate origin, others of tropical origin) to two freshwater snails, one from Eurasia, the other from South America.

Our results show that both the temperate and tropical snail herbivores preferred to eat plants with a high ratio of specific plant traits, namely the ratio of a feeding stimulant (nitrogen content, often related to protein) to a feeding deterrent (total phenolics content; phenols are defense compounds that contribute to the bitter or astringent flavor of tea). The preference of snails for novel or non-novel plants was inconsistent as both preferred temperate plant species, i.e. the tropical snail preferred novel plants and the temperate snail preferred non-novel plants. The difference in consumption rates of temperate and tropical plants was reflected in the nitrogen-to-phenolics content, which was higher in temperate than tropical plant species. These findings indicate that herbivore preference for plants depends on plant traits and the latitudinal origin of plants, not simply on the novelty of plants to herbivores. Overall, exotic plants from the tropics are less edible to temperate and tropical animals than plant invaders from temperate regions.

Image caption: Snail eating freshwater plants. Photos provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Climatic effects on population declines of a rare wetland species and the role of spatial and temporal isolation as barriers to hybridization

Katja Rohde, Yvonne Hau, Nicole. Kranz, Jasmin Weinberger, Ortwin Elle & Axel HochkirchImage provided by authors.

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Climate change and habitat fragmentation are known to have detrimental effects on the habitats of many wetland species and lead to new species compositions in these ecosystems. The impact of climate change on the interactions among species, particularly on interbreeding (hybridization) is, however, poorly understood. Hybridization can have severe consequences for the fitness of the species involved, as it might lead to genetic displacement of a species. Therefore, it is of particular interest for conservation practice to understand the effects of climate change and extreme weather events on population dynamics, population structure and hybridization.

We investigated the population dynamics of Ch. montanus (a rare, flightless grasshopper species which is strongly specialized on wetland habitats) and its sibling species Ch. parallelus, which is very widespread and common in many habitats. We hypothesized that climatic fluctuations have negative effects on the population trend of Ch. montanus. By studying the population dynamics over seven years and applying genetic methods, we further tested the hypothesis that Ch. montanus is more likely to hybridize with decreasing population size and that reproductive barriers (i.e. differences in the timing of the mating period, differences in mating behaviour or habitat affilitation) are altered by environmental changes.

We found that droughts and heavy rainfall are strongly correlated with population declines in Ch. montanus. Based on genetic and spatial analyses, we show that spatio-temporal segregation of both species provide an effective barrier to hybridization. However, this barrier can weaken if the Ch. montanus population decreases as the probability to encounter mates of the other species increases. This indicates that climatic extremes threaten rare species directly by reducing reproductive success and also indirectly by increasing hybridization risk.

Image caption: Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Causal relationships in food-web theory

Angelo B. Monteiro and Lucas Del Bianco FariaPhoto provided by authors.

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Ecological studies usually stress that natural communities are extremely diverse and possess a high degree of complexity. An early assumption was that this complexity promotes stability: damping the propagation of perturbations and regulating population outbreaks, while optimizing energy transfer between resources, consumers and predators. Later, however, a seminal paper used theoretical tools to assemble randomly constructed communities, and demonstrated that complexity was inherently unstable. In view of this paradox, food-web studies evaluate species trophic interactions (i.e. what eats what) to discover the mechanisms by which natural communities maintain stability despite the observed complexity. Historically, the two main research programs in food-web theory either emphasize the topological patterns in natural communities (i.e. how species are connected by feeding relationships), or the mechanisms regulating population dynamics. In this contribution, we explored the causal relationship between these two perspectives. We addressed two hypotheses: do particular topological patterns maintain population stability, or, alternatively, does population stability promote certain food-web topologies? Given that the process of collecting a large number of high-quality food-web data involves many practical problems, we simulated natural communities, but contrasted three different biological assumptions about trophic interactions. For each community, within each assumption, we measured three population-stability variables and two topological variables. Analyzing how these variables correlate, we could assemble path diagrams to infer causal relationships between them. Path diagrams measure the likelihood of each hypothesis generating the observed correlation, while evaluating if a given hypothesis is more likely than a random process. Our results demonstrated that population stability promoted food-web topology whatever the underlying assumptions about the trophic interactions. Thus, we demonstrated that only because population dynamics are stable (i.e. perturbations are damped and return to an equilibrium) are natural communities able to manifest certain topologies. These topologies are, for example, the presence of subgroups of taxa that interact more within that subgroup than with other subgroups; or the frequency of omnivorous behavior, in which, for example, a predator feeds on both the consumer and the basal resource. In addition, our results strongly support a recently proposed theory, which suggest that selection of stable topologies acts to shape natural communities into a single and consistent pattern.

Image caption: Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

An experimental test of state-behaviour feedbacks: gizzard mass and foraging behaviour in red knots

Kimberley J. Mathot, Anne Dekinga, and Theunis PiersmaRed knots. Image provided by authors.

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Red knots (Calidris canutus islandica) are shorebirds that feed on hard-shelled molluscs. They swallow these prey whole and crush them in their muscular gizzards (stomachs). Gizzard mass is remarkably flexible; knots increase gizzard mass in response to seasonal increases in energy demands, and in response to decreases in the digestive quality of their diets (i.e. ratio of digestible to indigestible components). Intriguingly, free-living knots exhibit consistent among-individual differences in gizzard mass. Given that gizzard mass is so flexible, what causes some individuals to maintain relatively large gizzards and others to maintain relatively small gizzards? One possible explanation is that there are positive feedbacks between gizzard mass and diet choice. It has previously been shown that a low digestive quality diet induces increases in gizzard mass. If larger gizzards in turn increase the probability of feeding on low quality diets, then even small, chance differences in gizzard mass and/or diet choice among-individuals could be maintained over time because the feedback between gizzard mass and diet choice would act to reinforce differences between individuals. We tested this idea experimentally using wild-caught red knots. Although experimentally determined diet quality had large effects on gizzard mass, the effect of experimentally manipulated gizzard mass on diet choice was weak at best. Furthermore, we observed consistent among-individual differences in gizzard mass even when animals did not have the opportunity to choose between items of different digestive quality. We conclude that positive feedbacks between diet choice and gizzard mass play at best a limited role in maintaining among-individual variation in gizzard mass in red knots. We suggest instead that social foraging interactions may play an important role determining the expression of behaviours (e.g. intake rate) that themselves influence gizzard mass. The possibility that group composition influences individual behaviour and organ mass is a new perspective, warranting further study.

Image caption: Red knots. Image provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

‘Reproductive effort and oxidative stress: effects of offspring sex and number on the physiological state of a long-lived bird

Thomas Merkling, Pierrick Blanchard, Olivier Chastel, Gaëtan Glauser, Armelle Vallat-Michel, Scott A. Hatch, Etienne Danchin & Fabrice HelfensteinKittwakes. Photo provided by authors.

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In an ideal world, individuals should maximize the transmission of their genes to the next generation by maximally investing in all activities related to reproduction and survival. However, such a ‘Darwinian demon’ does not exist because these activities draw on a common pool of limited resources. Consequently, individuals need to make allocation trade-offs between competing life-history traits, the physiological nature of which is largely unknown. Oxidative stress is defined as a deleterious accumulation of oxidative damage resulting from an imbalance between free radical production and antioxidant defences and/or repair mechanisms. Oxidative stress is hypothesised to underlie life-history trade-offs, because greater investment in reproduction may result in increased oxidative damage leading to faster bodily deterioration and reduced lifespan.

Despite a growing body of research, it is still unclear whether and how oxidative stress is involved in such trade-offs. Most studies to date have investigated the oxidative cost of natural or manipulated variation in offspring number. However, although the energetic requirements to producing sons or daughters can differ, the impact of variation in offspring sex-ratio on parental oxidative balance remains unexplored. Here, we studied how variation in offspring sex and number influenced several markers of oxidative stress and corticosterone levels in the black-legged kittiwake (Rissa tridactyla), a long-lived bird where sons are energetically costlier than daughters.

First, only individuals that could afford to invest heavily in reproduction did so. Those with higher pre-laying baseline corticosterone - known to facilitate higher parental workload - and lower antioxidant activity invested more in subsequent reproduction. Second, individuals rearing more sons had higher baseline corticosterone - both parents - as well as oxidative stress - mothers only - than those rearing daughters, and those rearing chicks for longer accumulated more oxidative damage to their lipids.

Our study provides the first evidence that brood sex-ratio can affect oxidative balance, potentially in a sex-specific manner, and highlights the need to consider offspring sex-ratio in future studies investigating the role of oxidative stress in life-history trade-offs.

Image caption: Kittwakes. Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Contrasting effects of climate and population density over time and life-stages in a long-lived seabird

Rémi Fay, Christophe Barbraud, Karine Delord and Henri WeimerskirchSPhotographic credit: Aurélien Prudor.

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Demographic processes of wild populations are affected by environmental variability. Such functional relationships have been extensively studied for many organisms but mainly through adult vital rates (e.g. adult survival and fertility). So far, early-life stages have strikingly been less studied because of the inherent difficulties in tracking the fate of young individuals. Yet, young organisms are expected to be more sensitive to environmental stochasticity owing to their inexperience and lower competitive abilities. Hence, this lack of information on the juvenile compartment of populations currently constrains our ability to fully understand population dynamics.

In this study, we investigated the effect of climate and population density on early-life demographic parameters of a long-lived seabird, the wandering albatross. We provided evidence that climate and population size affected both survival and age at first reproduction of young individuals, but in different ways according to the trait. In particular, although both early-life demographic parameters are affected by population density, we found that survival was more strongly impacted by density than age at first reproduction, showing different sensitivities to changes in population density. We also found a shift in the effect of population density on age at first reproduction, suggesting that density dependence mechanisms can temporarily disappear. In the context of globally decreasing seabird abundance, density dependent processes could be less evident but still essential to consider for long term population size projections.

With regard to environmental conditions, we showed that increasing sea surface temperature had a positive effect on young individuals becoming reproductive at a younger age, while at the same time, it had a negative impact on juvenile survival. We suggest that age-specific demographic responses to sea surface temperature observed in wandering albatrosses may be caused by the age-specific at sea distribution and thus local oceanic responses to climatic variation. Such results show that it is essential to consider age effects to understand population responses to climate change, since similar climatic conditions may have opposite effects on individual performances according to the life stage considered.

Such results are critical for our ability to make robust predictions on the impact of climate change on marine predators such as albatrosses.

Image caption: Photographic credit: Aurélien Prudor.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Leaf Dry Matter Content is better at predicting above-ground Net Primary Production than Specific Leaf Area

Simon Mark Smart, Helen Catherine Glanville, Maria del Carmen Blanes, Lina Maria Mercado, Bridget Anne Emmett, David Leonard Jones, Bernard Jackson Cosby, Robert Hunter Marrs, Adam Butler, Miles Ramsvik Marshall, Sabine Reinsch, Cristina Herrero-Jáuregui and John Gavin HodgsonExclosure. Photo provided by authors.

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We depend on plants to do something truly amazing: that is turning carbon dioxide and minerals into food using nothing more than water and sunlight. Because plants are so important it is no surprise that we have spent millennia moving them from place to place, cultivating them and feeding them to domesticated animals. Yet as well as providing food and timber they also do other amazing things for us for free like contributing to soil formation, providing nectar, helping stabilise the climate and even reminding us of the places where we have lived and worked. However we also know that the environment is changing in ways that are hard to predict. If changes in water supply, soil moisture, nutrient levels and climate alter the conditions for plant growth then, because we depend on plants so much, the free services that plants provide could also change in any one place. If that happens we need to know about it and plan for it. This means developing models that can estimate what a future environment might mean for plant growth. Getting these models right means basing them on good scientific understanding about which plant properties are the best indicators of the effect of environmental change and which are most closely linked to the things we need from plants. In our research we studied two properties of plant leaves that were known to be correlated with the production of vegetable matter. If an easy to measure property can predict plant production then this relationship could be used to help develop more accurate models and maps. In fact we found that the easiest property to measure, called Leaf Dry Matter Content, had the strongest correlation with plant production. It tends to be low for plants that grow quickly and produce more vegetable matter per year – think green grasses in the lowlands that cows like – versus plants that have a greater proportion of dry matter and grow more slowly – think Heather or Oak trees. The unique thing about our study was that we successfully measured productivity across an unusually large range; from high mountains through to lowland pastures.

Image caption: Exclosure. Photo provided by authors.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

The shape of fish success beneath the ocean waves

Sonia Bejarano, Jean-Baptiste Jouffray, Iliana Chollett, Robert Allen, George Roff, Alyssa Marshell, Robert Steneck, Sebastian Ferse, Peter J Mumby Fish in a reef. Photo credit: Dr. Mark Priest.

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Coral reefs dissipate large amounts of energy carried by ocean waves, and offer a broad spectrum of sheltered to powerfully turbulent habitats. Underwater, wave energy shapes the landscape of the seafloor, and affects the distribution of the associated fauna and flora. Coral reef fishes, essential for ecosystem services and ecological functions, are no exception. Herbivorous fishes in particular, play crucial roles in maintaining productive and healthy coral-dominated systems. Certain species are however considered slow swimmers, based on the shape of their fins, and tend to be excluded from turbulent habitats. The way herbivorous fishes and their feeding rates are further affected by wave exposure, based on their overall swimming performance, remains poorly understood.

In this study, we assess the swimming performance of 37 fish species using ten morphological traits related to swimming mode, speed, and manoeuvrability. We record their feeding frequency using video cameras on 12 sites distributed across sheltered, moderate, and turbulent reefs. We find that some species minimise drag through a hydrodynamic shape while others rely on tail propulsion. Feeding frequency is limited for certain species on turbulent reefs, while it is unaffected or increased for others.

There are important implications of these findings. Herbivorous fishes have been classified in four subgroups capable of feeding on different types of algae. Subgroups are usually considered complementary to each other, and species within subgroups are often viewed as functionally redundant, meaning that they can replace each other. However, we find that two important subgroups (grazers and scrapers) and the species within them respond differently to wave exposure. The fact that grazers responded differently to wave exposure compared to scrapers emphasises their distinctness and complementarity. Because certain grazers and scrapers responded differently to wave exposure compared to their counterparts, we highlight the risk in regarding species within subgroups as redundant. We therefore challenge the way biodiversity is often perceived and confirm that species presence does not imply their complete functionality, especially under harsh environmental conditions. We demonstrate that neither redundancy nor complementarity, which are desirable attributes of communities and prerequisites for resilient systems, should be assumed to be homogeneous throughout heterogeneous systems.

Image caption: Fish in a reef. Photo credit: Dr. Mark Priest.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

 

Goldenrod “eavesdrops” on the communication of its specialist herbivore and defends itself in proportion to its proximity to the communication source

Eric C. Yip, Consuelo M. De Moraes, Mark C. Mescher and John F. TookerPhotograph by E.C. Yip.

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Plants often employ chemicals that deter feeding to defend themselves from herbivores; however, if plants allocate resources to defensive chemicals, they may have fewer resources left for growth and reproduction, thereby making these defences costly. To mitigate the cost, defensive chemicals are often not continuously produced, but rather deployed only after herbivore attack. Plants can further anticipate attack and accelerate defence deployment by “priming” defences in response to cues that indicate future herbivory. We recently discovered that goldenrod (Solidago altissima) primes itself for defence by “eavesdropping” on the chemical communication of its specialist herbivore, the gall fly Eurosta solidaginis. Male flies perch on the tips of goldenrod and release an airborne chemical blend that attracts females. When exposed to this chemical emission, goldenrod increases its defensive chemistry and suffers less damage from herbivores. In this experiment, we examined the distance the priming signal extends from the fly by monitoring stems at varying distances from a central stem caged with a male fly. Leaf damage increased with distance from the fly, suggesting that, as the chemical signal dissipates, plants prime themselves to lesser degrees. Contrary to the predicted trade-off between plant defence and growth, stems caged with flies grew faster than stems without flies; however, increased growth and defence early in the season did not result in greater flower production, as stems caged with flies produced a similar number of flowers as those stems farthest from the fly. Instead, stems that were a mid-distance from the fly experienced decreased growth and flower production. The gradation of plant defence surrounding each fly is likely important in goldenrod fields, where individual stems are often only a few centimetres away. As herbivores move from more to less defended plants, they might alter their distributions, with possible ramifications for the entire goldenrod community. Our finding that stems a mid-distance from the fly were shorter with fewer flowers suggests that the ultimate consequences of priming on the reproductive success of plants may be complex and require further investigation.

Image caption: Photograph by E.C. Yip.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. You can find the As Accepted version here.

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