Lay Summaries: Volume 26, Issue 1

Volume 26 Issue 1

  • Setting the trap: cleaning behaviour of Camponotus schmitzi ants increases long-term capture efficiency of their pitcher plant host, Nepenthes bicalcarata Thornham et al
  • The effect of plant architecture on drought resistance: Implications for the evolution of semelparity in Erysimum capitatum Kim et al
  • Early resistance of alien and native pines against two native generalist insect herbivores: no support for the natural enemy hypothesis Carrillo-Gavilán et al
  • Deleterious effects of light exposure on immunity and sexual coloration in birds Orledge et al
  • Impact of clear and cloudy sky conditions on the vertical distribution of photosynthetic CO2 uptake within a spruce canopy Urban et al
  • The foraging tight-rope between predation risk and plant toxins: a matter of concentration McArthur et al
  • Functional ecology of saltglands in shorebirds: flexible responses to variable environmental conditions Gutiérrez et al
  • Deleterious effects of light exposure on immunity and sexual coloration in birds Blount & Pike
  • Plastic responses to four environmental stresses and cross-resistance in a laboratory population of Drosophila melanogaster Bubliy et al
  • Contrasted breeding strategies in four sympatric sibling insect species: when a proovigenic and capital breeder copes with a stochastic environment. Pélisson et al
  • Transcriptome profiles link environmental variation and physiological response of Mytilus californianus between Pacific tides Place et al
  • Effects of human-mediated pollinator impoverishment on floral traits and mating patterns in a short-lived herb: an experimental approach Brys and Jacquemyn
  • Behavioural trait variants in a habitat forming species dictate the nature of its interactions with and among heterospecifics Pruitt et al
  • Metabolic theory, life history, and the distribution of a terrestrial ectotherm Kearney
  • Scaling of lunge feeding performance in rorqual whales: mass-specific energy expenditure increases with body size and progressively limits diving capacity Goldbogen et al
  • Wood density explains architectural differentiation across 145 co-occurring tropical tree species Iida et al
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    Setting the trap: cleaning behaviour of Camponotus schmitzi ants increases long-term capture efficiency of their pitcher plant host, Nepenthes bicalcarata

    Daniel G. Thornham, Joanna M. Smith, T. Ulmar Grafe and Walter Federle

    There are more than 600 species of plants worldwide known to capture small animals to obtain extra nutrition. One species in the tropical peat swamp forests of Borneo, the fanged pitcher plant, Nepenthes bicalcarata, not only traps insects, but also provides a home for the highly specialised species of carpenter ant, Camponotus schmitzi.

    The plant's leaves are specially modified as cup-shaped insect traps. These pitchers produce sweet nectar to lure insects; slippery surfaces on the upper rim of the pitcher cause them to slide and fall into the pitchers where they are held and digested by the fluid within. Amazingly, the resident Camponotus schmitzi ants appear to be completely immune to the traps; they nest inside hollow stems of the plant, feed on the traps' nectar without falling and "steal" prey from the pitchers by swimming and diving in the digestive fluid.

    Many "ant-plants" have evolved close relationships with ants, which can provide protection from leaf-feeding insects and fungal attack, in return for nesting space and food rewards. The fanged pitcher plant is the only known insect-eating ant-plant. Despite a number of studies since its discovery in the late 19th century, it has been unclear what, if anything, the plant gains from the association.

    We discovered that the Camponotus schmitzi ants thoroughly clean the slippery trapping surface of their host plant. Even when strongly contaminated by cornflour, the ants' cleaning restored the slipperiness of the trap within a few days. By cleaning the slippery trap, the ants ensure it is maintained in good condition and can continue to capture insects for much longer than if the ants are absent. Indeed, the pitchers of Nepenthes bicalcarata can live and remain active three times longer than pitchers from other Nepenthes species in the area. So, by maintaining the traps of the plant, the ants do more than just clean: they help the plant to be well-fed.

     

    The effect of plant architecture on drought resistance: Implications for the evolution of semelparity in Erysimum capitatum

    Eunsuk Kim and Kathleen Donohue 

    Alpine environments are among the most endangered habitats because of climate change. Increased temperature is predicted both to reduce the absolute area of alpine habitat, and also to induce drought conditions. With climate change, therefore, alpine plants may face novel drought stress. Determining how alpine plants respond to drought conditions provides insight into how climate change would alter organismal performance, and thereby influence population viability and species ranges and abundance in threatened habitats.

    Western Wallflower (Erysimum capitatum) inhabits a very broad altitudinal range from below the tree-line (1500m altitude), where drought is common, to the alpine tundra (over 4000m altitude) in the Colorado Rocky Mountains. This distribution allows us to quantitatively evaluate whether alpine plants have weaker drought resistance compared to those in lower elevation. In addition, alpine Western Wallflowers reproduce multiple times because although the main rosette dies after flowering, they develop rosettes in their leaf axils (referred to as "axillary rosettes") that can survive from year to year. In contrast, Wallflowers in lower elevation rarely produce persistent axillary rosettes and therefore reproduce only once. In this paper, we tested whether the development of axillary rosettes by plants from high elevation made them more susceptible to drought stress.

    We found that under drought conditions, fewer alpine plants survived, and for a shorter time, compared to those from low-elevation environments, and such differential survival was in part accounted by the presence of axillary rosettes. These results suggest that alpine Western Wallflowers would suffer increasing mortality if drought stress were to occur in alpine environments due to climate change, possibly resulting in decreased population size. Moreover, the results imply that selection for drought tolerance, via reduced rosette production, could influence overall life-history, since axillary rosettes enable a perennial life history with reproduction over many years, as opposed to the single reproductive of plants without axillary rosettes. Thus selection on physiological tolerances to altered climates has the potential to alter fundamental life history.

     

    The attack of native generalist herbivores: are alien better defended than native pines?

    Amparo Carrillo-Gavilán, Xoaquín Moreira, Rafael Zas, Montserrat Vilà and Luis Sampedro 

    Most of the concern regarding alien conifer invasions has been voiced in the Southern Hemisphere while in the Northern Hemisphere, although many alien conifers were introduced and widely planted in the past century, but few conifer invasions have been reported. The success of alien plants in their new range depends partially on the interaction with native enemies, particularly with herbivores that could damage establishing seedlings. The Natural Enemy Hypothesis (NEH) predicts that alien plant species might receive less pressure from natural enemies than coexisting native related plants in the introduced range. However, the level of attack by native generalist herbivores can vary considerably between plant species depending on their defensive strategies such as chemical defences (plant chemical defences include: constitutive defences, which are permanently expressed; and induced defences, which enhance the basal defence capacity after a natural-enemy attack).

    We performed an experiment with seedlings of 9 alien and native pine species to Europe, and studied both damage and induced chemical defences after exposure to two native European generalist herbivores (the pine weevil Hylobius abietis and the pine processionary moth Thaumetopoea pityocampa). We expected that, as predicted by the Natural Enemies Hypothesis, generalist herbivores would cause lower damage to alien than to native pine species. But, we also expected that alien plants exposed to generalist native herbivores would induce weaker defences than would native pines, due to a lack of a shared evolutionary history.

    Our results did not support the prediction made by the NEH that native herbivores would avoid alien plants due to a lack of recognition. And, in relation to chemical defences, our results also suggest that alien pines, in regions where they coexist with native relatives, are not well defended and might be controlled by native generalist herbivores. This might be one reason why invasion by alien pines is not frequent in Europe.

     

    Synergistic effects of supplementation of dietary antioxidants during growth on adult phenotype in ring-necked pheasants, Phasianus colchicus.

    Josephine M. Orledge, Jonathan D. Blount, Andrew N. Hoodless, Thomas W. Pike, Nick J. Royle.

    Resources are finite, so allocation to one function means resources cannot be allocated to another, competing, function simultaneously. These trade-offs are important in shaping the life-history evolution of organisms, especially for species with elaborate sexual ornaments, such as ring-necked pheasants, where males have colourful plumage and fleshy, red, facial wattles that are attractive to females but costly to produce. Little is known about the mechanisms underlying resource allocation trade-offs, but oxidative stress is a strong candidate. Oxidative stress occurs when there is an imbalance between the production of potentially damaging reactive oxygen species (ROS), which are by-products of normal metabolic processes, and antioxidant defences, in favour of the former. An important component of antioxidant defences are dietary-derived antioxidants such as carotenoid pigments, which provides the colour of the facial wattles of pheasants, and vitamin E. Recent work on a number of different species indicates that antioxidants may have effects on the expression of ornaments. Carotenoids cannot be used as pigments if they are used as antioxidants, so the availability of non-pigmentary antioxidants such as vitamin E may be necessary to make carotenoids available for sexual display. However, these studies do not take account of trade-offs during development. Growth involves high production of ROS, but competition for resources favours rapid growth, which may come at the expense of self-maintenance (i.e., future sexual ornaments) unless mitigated by antioxidants.

    We tested the effects of supplementation during early growth of carotenoids and vitamin E, singly and in combination, on the expression of sexual ornamentation in adulthood in male pheasants. We found effects of antioxidant supplementation, but not as expected. Males given a combination of vitamin E and carotenoids were larger at adulthood but there were no effects of supplementation on the size, shape or colour of sexual ornaments. This suggests that in pheasants limited resources in early life are preferentially allocated towards traits that increase competitive ability with other males rather than attractiveness to females.

     

    Impact of clear and cloudy sky conditions on the vertical distribution of photosynthetic CO2 uptake within a spruce canopy

    Otmar Urban, Karel Klem, Alexander Ac, Katerina Havránková, Petra Holišová, Martin Navráti, Martina Zitová, Klára Kozlová, Radek Pokorný, Mirka Šprtová, Ivana Tomášková, Vladimír Špunda, John Grace

    Cloud cover increases the proportion of diffuse radiation reaching the Earth's surface and affects many microclimatic factors such as temperature and vapour pressure deficit, and may thus affect carbon exchange between plants and the atmosphere. Recent studies have demonstrated that an increase in the fraction of diffuse radiation can enhance the photosynthetic efficiency of canopies. Although the exact mechanism behind this effect is not clear, a more even distribution of light among leaves through the vertical profile of the canopy is considered to be the most important cause of the observed difference.

    To test this hypothesis, the net carbon uptake of a whole 30-year-old Norway spruce forest under cloudy and sunny skies was estimated. In parallel, shoot-level measurements of the daily course of CO2 uptake were made in the sunny upper, middle, and shady lower parts of the canopy.

    The higher diffuse radiation fraction during cloudy days resulted in higher ecosystem carbon uptake than at equivalent light intensities on sunny days. Our shoot-level data show that shoots from deep within the canopy contribute substantially to the overall carbon balance during cloudy days, whereas the contribution of the middle and shaded parts of the canopy is only marginal or even negative during sunny days.

    In addition, during sunny days the canopy carbon uptake and CO2 assimilation rates of the uppermost shoots were depressed in the afternoon in response to the high irradiance, characterized by decreases in CO2 uptake. This effect was not observed under cloudy conditions. Substantial afternoon stomatal closure associated with shortage of water on sunny days has been identified as the most important reason behind this effect.

    Diffuse radiation thus has important effects on the productivity and structure of vegetation. Increased penetration of light into the canopy, and more efficient use of this light under diffuse light conditions may explain how forests with dense canopies can maintain significant carbon uptake, despite a high degree of self-shading by individual shoots. Forest canopies are thus well adapted to the most common light environment that they encounter. We can expect that if a forest is growing at a site where conditions are predominantly cloud they will have a dense canopy.

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    The foraging tight-rope between predation risk and plant toxins: a matter of concentration

    Clare McArthur, Paul Orlando, Peter Banks and Joel Brown

    Plants defend themselves from being eaten and predators attack prey in order to eat. Together, these provoke an important foraging dilemma for animals that eat plants (leaf- and fruit-eaters) but that are themselves prey: how to eat enough without being eaten. Plant-eaters are often limited in how much they can eat because of naturally-occurring toxins in leaves and fruit. The higher the toxin concentration, the less they can eat. Meanwhile they also risk being eaten by predators. They must respond to this predation risk, but this constrains where (and when) they can forage. Thus the foraging landscape of plant-eaters is defined by both the costs of plant toxins and predation risk. How foraging animals directly quantify, compare and respond to these two costs has rarely been tested.

    We show that thick-tailed bushbabies-small, fruit-eating primates-change how they behave and the extent to which they use artificially-created patches of food in their natural habitat, based on the interplay between the toxin concentration of the food and how safe the food patch is. We ran a titration experiment, similar in concept to a school chemistry experiment, where we varied the concentration of a plant toxin in safe food patches and kept the risky food patches toxin-free. We demonstrate that these animals quantify the relative costs of toxin and fear. We pinpoint where these costs are equivalent and show that animals seek food patches with the lower net cost, irrespective of whether the cost comes from food or fear.

    We conclude that the effectiveness of plant toxin as a defence against plant-eaters depends not only on its concentration in food, but also on how risky the environment is. A corollary is that plants can benefit from fear as a substitute for their own defence: plants can be defended from plant-eaters by predation risk rather than by being toxic. The concept of indirect plant defence refers to plants benefiting from natural enemies of plant-eaters, generally by attracting these enemies. Predation risk can be seen as a new dimension to this defence, albeit one over which the plant has less control.

     

    Functional ecology of saltglands in shorebirds: flexible responses to variable environmental conditions

    Jorge S. Gutiérrez, Maurine W. Dietz, José A. Masero, Robert E. Gill, Jr., Anne Dekinga, Phil F. Battley, Juan M. Sánchez-Guzmán and Theunis Piersma

    Many species of birds live or feed in saline environments for most of their lives. To cope with salt stress, these birds have specialized glands-called saltglands-that are located on the skull between eyes. These glands extract salt ions from the bloodstream and produce a concentrated salt solution that is discarded through the nostrils. Excreted salt may be visible as 'water'drips off the tip of the beak. Previous studies have shown that both the size and excretory capacity of these organs vary as a function of habitat salinity and dietary salt, that is, saltglands are larger and more efficient in species and individuals that have higher salt loads. However, saltgland size is not always correlated with these factors, and often shows marked seasonal variation.

    Here we went one step further and examined how climatic conditions, prey type and energy requirements affected saltgland size of shorebirds. To do this, we made comparisons across and within 29 species of shorebirds that differ in habitat, diet and ambient temperatures. For a more detailed picture of the importance of energy requirements and ambient temperature in saltgland mass, we focused on two long-distance migrants with a world-wide distribution (red knot Calidris canutus and bar-tailed godwit Limosa lapponica).

    Our results supported the notion that salinity of habitat and the salt content of the diet to a large extent explain variation in saltgland size. When considering marine species only, mollusc-eaters had larger saltglands than those eating non-shelled prey, indicating that seawater contained within the shells added to the salt load. In both bar-tailed godwits and red knots, saltgland mass was positively correlated with intestine mass, an indicator of relative food intake rates (salt loads). Additionally, red knots showed an increase in saltgland mass at both low and high temperatures, which probably reflects increased energy demand for temperature regulation at low temperatures and elevated respiratory water loss at high temperatures. We can conclude that shorebirds adjust the mass of this small but essential piece of metabolic machinery to successfully overcome the osmoregulatory challenges faced in the course of their lives.

     

    Deleterious effects of light exposure on immunity and sexual coloration in birds

    Jonathan D. Blount and Thomas W. Pike

    Light can be thought of as both friend and foe, being essential for tasks such as foraging and mate choice, while at the same time having the potential to cause serious damage to biological tissues. In particular, studies of humans and rodents have shown that sunlight can damage cells and impair the immune system. There is also recent evidence that sunlight causes fading of sexual colouration in birds - particularly those signals produced by red and yellow carotenoid pigments. However, whether sunlight may simultaneously affect sexual colouration, cell damage and immunity has not been studied before. If so, it seems possible that a faded sexual signal could reveal an individual's history of sunlight exposure and the damaging effects this has had on its health - this could be useful information for prospective mates.

    We investigated the effects of exposure to simulated sunlight, coupled with dietary carotenoid supplementation, on sexual colouration, cell damage and immunity in zebra finches (Taeniopygia guttata). We found that simulated sunlight exposure caused extensive depletion of sexual colouration, and triggered mobilisation of carotenoid pigments from storage in body tissues. Light in the ultraviolet (UV) wavelength range was particularly damaging, causing impaired immunity, but this was not seen in birds which had access to plentiful dietary carotenoids.

    Our results show that carotenoid-based sexual colouration is highly susceptible to fading caused by light, and that this is linked to an individual's physiological state in terms of its immunity. These novel findings could have far-reaching implications for our understanding of the evolution of colourful sexual signals, and raise some intriguing new questions. For example, do birds avoid excessive exposure to sunlight, particularly in environments where there is a high risk of disease and maintaining a strong immune system is vital? If birds must sometimes avoid sunlight, does this impinge on their ability to find food or to mate?

     

    Plastic responses to four environmental stresses and cross-resistance in a laboratory population of Drosophila melanogaster

    Oleg A. Bubliy, Torsten N. Kristensen, Vanessa Kellermann and Volker Loeschcke

    Animals and plants can respond to changes in their environment in two different ways: 1) through evolutionary changes over multiple generations and 2) via plastic changes within a lifetime. Plastic physiological response can be induced by experimental treatments, for instance, by exposure to high or low stressful temperatures. The responses to such treatments are referred to as acclimation or hardening, where the latter term is often used for short-term exposures and generally more severe conditions. There is evidence that acclimation/hardening to one type of environmental stress in arthropods can lead to a plastic response, which then confers increased resistance to other stresses. This phenomenon, called "cross-resistance", may indicate shared physiological resistance mechanisms and a possibility of joint evolution for resistance traits.

    In the present study we tested for cross-resistance using the fruit fly Drosophila melanogaster. As stressful treatments we considered cold acclimation, heat hardening, desiccation hardening and starvation acclimation, which are associated with plastic changes in response to four common stresses in the natural environment of many insects. After each acclimation or hardening treatment we estimated survival of flies under extreme cold, heat, desiccation and starvation conditions that allowed the assessment of potential cross-resistance effects. The treatments were chosen so they increased resistance to later exposures to similar types of stress, e.g. heat hardening increased resistance to later exposure to heat stress. Out of a total of 12 exposures of acclimated flies to different stresses, we found two cases of cross-resistance, four with no acclimation/hardening effect and six cases with a negative effect of acclimation/hardening. Additionally, we discovered that all treatments except cold acclimation led to reduced longevity of flies under non-stressful laboratory conditions.

    Thus our study demonstrated the prevalence of negative effects of acclimation/hardening both across different stressful environments and in an optimum environment, an effect often referred to as an acclimation cost. The lack of cross-resistance induced by acclimation/hardening treatments suggests that in a multiple-stress environment plastic response may not safeguard the persistence of populations and that evolution of shared physiological protective systems associated with this kind of adaptation may be constrained.

     

    Making sense of heat tolerance estimates in ectotherms: lessons from Drosophila

    PF Pélisson, MC Bel-Venner, B Rey, L Burgevin, F Martineau, F Fourel, C. Lecuyer, F Menu and S Venner

    The way animals acquire their energy from nutrients and allocate it to various physiological processes is a central issue for all living organisms. How such strategies evolved largely depends on the degree of environmental variability experienced by organisms. Breeding is one of the most energy-demanding activities, and female insects are known to acquire energy and to allocate it to reproduction possibly using one of two well described, contrasting strategies. The first one consists in storing nutrients during the larval stage and allocating them to egg manufacturing soon after the adult emerges. This rigid strategy is considered to be optimal in highly predictable environments. The second strategy consists in covering the adult needs using the energy gained concurrently through adult feeding. This strategy notably enables the females to adjust the production of mature eggs to the availability of egg-laying sites. Owing to that flexibility, it is considered to be optimal in highly unpredictable and variable environments.

    We studied communities composed of four closely-related insect species that commonly experience great unpredictability and strong between-year fluctuations in the number of nesting sites available, to test the prediction that females from all these four species have evolved the same, flexible strategy of energy acquisition and allocation to reproduction. Unexpectedly, our results show that while three of these species effectively adopted a flexible strategy that allows them to produce more eggs when environmental conditions are favourable, one of them clearly adopted a non-flexible strategy and exclusively used energy of larval origin to breed. These findings thus suggest that a highly fluctuating environment, instead of promoting a unique, optimal strategy of energy acquisition and allocation to reproduction, should favor their diversification.

     

    Transcriptome profiles link environmental variation and physiological response of Mytilus californianus between Pacific tides

    Sean Place, Bruce Menge, Gretchen Hofmann

    The marine intertidal zone is characterized by large variation in temperature, pH, oxygen and food availability. These oceanic fluctuations are recognized as major drivers of many ecological processes such as recruitment of new individuals, competition, and consumer-prey interactions that help set the patterns of species distributions we see today. To understand what future populations might look like, it is important to understand the mechanisms that play a role in setting physiological limits and what options remain available to marine organisms as the climate continues to change.

    For existing populations of many sessile organisms, such as the California ribbed mussel, Mytilus californianus, migration is not an option. Evolutionary responses may benefit the species in some longer time frame, but are similarly not available to existing mussels. Therefore the only option available to existing populations is to alter their physiology in an effort to cope with changing environments. So to understand how these species might be impacted, we need to have a deeper understanding of the way environmental variation leads to biological changes in an organism under more realistic habitat conditions.

    Here, we have applied technologies that allow us to examine the activity of thousands of genes simultaneously, to gain insight into the response of mussels to natural environmental variation. In our results, we report on the coordinated changes in expression of metabolism and stress response genes in different mussel populations, and link these changes to natural variation in food availability and temperature. We found no important variation among individuals inhabiting the same relative tide height within the intertidal zone, strong variation in stress responsive genes in mussels inhabiting different vertical positions within a single mussel bed, and differences in mussel populations separated by ~ 65 km that are related primarily to differences in food availability. These data highlight how these environmental variables may work together to lower stress tolerance, and could have important implications for future efforts aimed at predicting the impact of climate change on populations that span large biogeographic distributions.

     

    Effects of human-mediated pollinator impoverishment on floral traits and mating patterns in a short-lived herb: an experimental approach

    Rein Brys and Hans Jacquemyn

    Recent research indicates that pollinator populations across the globe are declining. This finding has been a prominent feature in recent news stories and headlines in the popular press. It is indeed expected that a large fraction of plants that rely on animal pollinators may suffer reduced reproduction, and under some circumstances reductions of their populations. Apart from such ecological effects that are of immediate concern, little attention is given to the potential evolutionary consequences.

    In this study we investigate the impact of human disturbances of the pollinator environment on the short-lived common centaury (Centaurium erythraea). We selected natural populations occurring under contrasting pollinator environments: populations occurring in pollinator-rich coastal dune grasslands vs. chronic pollinator-limited populations occurring in an industrial area. C. erythraea is an insect-pollinated herb that prefers to reproduce via outcrossing when pollinators are present, but when unvisited, flowers are to some extent able to self-pollinate autonomously. This can happen because the pollen-producing structures (anthers) curl at the end of a flower's life-span and deposit some of their pollen on the female receptive surface (stigma). Anthers and stigma are, however, spatially separated in the flower (known as herkogamy), and the level of herkogamy may determine a plant's capacity for autonomous self-pollination.

    We show that severe pollinator impoverishment selects for smaller flowers with little or no herkogamy, which are better able to self-fertilize when remaining unvisited. To understand in greater detail the consequences of pollinator scarcity, we applied a reciprocal translocation experiment in the field combined with supplemental hand-pollination of some plants and emasculation (removal of the stamens) of others. This allows to test the hypothesis that pronounced differences in pollinator availability resulted in significant differences in pollen limitation and pollination patterns, and whether these effects were mediated by the observed differences in floral traits. When exposed to the pollinator-rich environments, plants from pollinator-limited populations showed much lower pollinator-mediated seed set than the original plants. In contrast, plants from pollinator-rich environments exposed to the pollinator-poor environment, did not experience higher pollinator-mediated seed production and showed lower total reproductive output than plants originally occurring in these pollinator-limited environments.

    These findings clearly show that human-induced pollinator shortages may select for selfing plants with smaller flowers, whereas in pollinator-rich environments floral traits are selected to support pollinator-mediated outcrossing.

     

    Behavioural trait variants in a habitat forming species dictate the nature of its interactions with and among heterospecifics

    Jonathan Pruitt, Julien Cote & Maud Ferrari

    Spiders are notorious for their aggression, but a handful of among the roughly 40,000 species express highly tolerant, cooperative behavior. However, the tolerant behavioral tendencies of social spiders come with a cost, and colonies frequently and unwillingly harbor foreign spiders that prey on colony members and steal their food. Like humans, not all social spiders behave the same way, and individuals can be roughly categorized as "docile" or "aggressive" based on their performance in a smattering of behavioral tests; in other words, even within a colony, individual spiders exhibit characteristic personality types. In this study we investigate how mixture of personality types within colonies influences colony members' reproductive success when in association with foreign spiders, and how the mix of personality types impacts the growth rate of the foreign spiders themselves.

    We found that colonies containing aggressive females produced smaller egg cases with fewer eggs when in association with foreign spiders, and foreign spiders tended to gain weight slowly. In contrast, groups of all docile females actually produce larger egg cases and more eggs when in association with foreign spiders, and foreign spiders gained weight very rapidly. The results are striking because not only does the personality composition of spiders' social groups change the relative performances of both colony members and foreign spiders, it actually changes the nature of their relationship from a parasitism, where colony members are hurt and foreign spiders benefit, to a mutualism, where both colony members and foreign spiders benefit. However, the effects of personality don't stop there. In fact, the mixture of personality types within colonies even changes the way foreign spiders interact with each other! In colonies containing aggressive females, foreign spiders must compete with each other for access to prey and negatively affect one another's weight gain. In contrast, in groups of all docile females, foreign spiders positively impact each other's weight gain. Our results highlight the fact that the way individuals and species interact with each other can depend on personality types of the individuals involved, and thus, even in the seemingly least likely of candidates (spiders), we are reminded that personality impacts the way individuals interact with their world.

     

    Metabolic theory, life history, and the distribution of a terrestrial ectotherm

    Michael Kearney

    Some of the most fundamental ecological questions we can ask about a species are how fast it grows, when it matures, how large it gets, how many babies it produces and how often it reproduces. These are all questions about life history. The life history may vary dramatically across environmental gradients such as temperature, especially in cold-blooded animals (ectotherms) whose body temperatures vary dramatically with environment. If we can predict how these life history characteristics vary through space and time, we can potentially make important inferences about a species' distribution and abundance. However, to make these predictions with the greatest reliability and generality, we need to ground them as much as possible in the fundamental principles of chemistry and physics.

    In this study I bring together two complementary first-principles methods for understanding a species' life history in changing environments: biophysical ecology and dynamic energy budget theory. Biophysical ecology involes the application of heat transfer physics to organisms and allows accurate predictions of body temperature and potential activity time, even in the complex microclimates found in terrestrial habitats. Dynamic energy budget theory similarly applies thermodynamic principles to provide a powerful and general way to model individual metabolism, i.e. how an organism takes up energy and matter from its environment and uses it for growth, maintenance, maturation and reproduction across its whole life cycle. These two methods are complementary because metabolism determines factors such as body size which affect body temperature, while body temperature itself affects the rates of metabolism and when the organism can leave its retreat and feed.

    I apply these integrated models with climate data to study the life history and geographic distribution of a very well studied terrestrial ectotherm from North America, the Eastern Fence Lizard. The method successfully predicts how its life history varies across its range through the combined effects of body size and temperature, and ultimately how these changes place limits on its potential distribution. The approach is readily adaptable to other kinds of animals and should be a powerful tool for predicting how species will respond to environmental change.

     

    Scaling of lunge feeding performance in rorqual whales: mass-specific energy expenditure increases with body size and progressively limits diving capacity

    Goldbogen, Jeremy; Calambokidis, John; Croll, Donald; McKenna, Megan; Oleson, Erin; Potvin, Jean; Pyenson, N.; Schorr, Greg; Shadwick, Robert; Tershy, Bernie

    Body size is one of the most important factors that determine how animals function. In general, larger animals have more efficient metabolic rates and this confers a multitude of physiological advantages. Among diving marine mammals and birds, larger animals have more oxygen stores within their body and they use oxygen more efficiently during a dive. As a consequence, larger animals have the ability to dive longer and therefore can more readily exploit potentially higher quality prey patches at greater depths.

    We tested this hypothesis by assessing the performance of foraging dives in a family of baleen whales called rorquals, which includes humpback, fin, and blue whales. Like all baleen whales, rorquals filter prey from water using keratinized plates of baleen that hang down from the top of the mouth. However, rorquals are distinguished from other baleen whales by their unique lunge feeding strategy, in which the mouth opens very wide and engulfs a huge volume of water - sometimes more than its own weight - together with any krill in the water. Forcing all this water into its distended mouth generates a lot of drag. The amount of water that is engulfed and the amount of drag incurred during lunge feeding is determined by the size of the mouth. In larger whales the size of the skull is larger relative to body size, which effectively enhances the amount that can be engulfed.

    Here we show that this scaling effect increases the relative energetic cost of lunge feeding in larger whales, where blue whales expend proportionally more energy to feed than smaller fin and humpback whales. As a result, diving capacity is progressively limited in larger rorquals; humpback whales were able to dive just as long as blue whales. Because dive time is limited in larger rorquals, they cannot perform as many lunges as smaller whales. It appears that larger whales forfeit the typical advantages associated with large body size, namely enhanced diving capacity, in order to take larger gulps of water and prey. Such a trade-off may underlie particular prey preferences, resource partitioning, ecological niche, and life history in different rorqual species

     

    Wood density explains architectural differentiation across 145 co-occurring tropical tree species

    Yoshiko Iida, Lourens Poorter, Frank Sterck, Abd Rahman Kassim, Takuya Kubo, Matthew Potts, Takashi Kohyama

    Growing taller and wider are the two main ways trees capture light in a crowded forest. We expect that the observed variation in tree height and crown width (tree architecture) across species in tropical rainforest reflects species differences in light capture strategies. A recent mechanistic theory makes specific predictions concerning the relationship between wood density and tree architecture: high wood density is efficient for horizontal branch expansion, whereas low wood density is efficient for vertical stem expansion. We tested these predictions by investigating variation in wood density and tree architecture among 145 co-occurring tree species in a Malaysian rainforest, sampling species through a wide size range from saplings to adult trees. Our results supported mechanical constraints predicted by the theory and showed that differences in wood density as well as maximum attainable size are independently related to tree architecture. Species with low wood density grow taller to reach better light conditions in the exposed canopy, while species with high wood density grow wider crowns to enhance light interception and persistence in the shaded forest understorey. We conclude that wood density and maximum attainable size are two essential traits that determine species tree architecture and affect species light capture strategy in tropical rainforests.

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Ecology of Exercise
Advances and Challenges in the Study of Ecological Networks
Virtual Issue: Towards a mechanistic understanding of global change ecology
30 years of Functional Ecology
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