Functional EcologyBritish Ecological Society
 

Lay Summaries

The below summaries are provided by our authors to help put their research paper into context for the wider scientific community and the general public.

 

The consequences of a “good mom, bad mom” scenario in pythons

Zachary Stahlschmidt, Richard Shine and Dale DeNardoPython with eggs. Photo by Zachary Stahlschmidt

Many animal parents provide care for their offspring. Although beneficial to developing offspring, parental care typically comes at a cost to parents. The population of water pythons (Liasis fuscus) we studied offered a unique opportunity to examine the benefits and costs of parental care. Some female pythons are “good moms”—they attend (“brood”) their eggs for two months (“long brooders”) until their offspring hatch. In comparison, other females are “bad moms”—they brood for only one week (“short brooders”) before abandoning their nests. We used radiotracking, temperature and humidity data loggers, ultrasound technology, blood analysis techniques, and habitat analyses to examine the consequences of females’ nesting decisions.

In general, both females’ choice of nests (which were warmer, more humid, and more stable than the surface environment) and their egg brooding improved the temperature and humidity in which their offspring developed. However, long brooders kept their offspring at a more favorable temperature prior to egg laying (when the eggs were still inside the females), and they chose warmer, more humid nests. Thus, offspring of long brooders experienced beneficially warmer and more humid conditions throughout development. Reproduction was costly to females because they lost 60% of their weight and suffered increased parasite burdens. However, the amount of weight lost during brooding was low (<5%) and was not different between short and long brooders. The existence of both “good moms” and “bad moms” in this population may be due to a tradeoff between offspring number and quality. Short brooders can reproduce more frequently, because brooding for a short time means they have more time to recover body reserves lost to egg production. Thus, short brooders may invest in more clutches throughout their lifetimes but care for them poorly (they choose quantity over quality), while long brooders invest in fewer clutches but care for them well (they choose quality over quantity).

Image caption: Python with eggs. Coutresy of Zachary Stahlschmidt.

 

Belowground plant species richness: new insights from DNA-based methods

Meelis Pärtel, Inga Hiiesalu, Maarja Öpik and Scott Wilson

Biodiversity is a primary focus of both theoretical and experimental ecology. Until very recently, plant species diversity and coexistence theories were entirely based on aboveground data. In contrast, many widespread ecosystems of temperate, arid and polar regions, such as grassland, steppe, desert and tundra, have >50% of plant production or biomass belowground. The measurement of species richness of this large belowground component has been hindered by the difficulty of assigning roots and rhizomes to species. Current DNA-based methods now allow belowground richness to be studied in the field. Here we provide a concise overview of how the use of DNA-based techniques might alter our perception of richness patterns in plant communities. DNA-based measurements of belowground plant richness are likely to reveal that plant richness is greater below- than aboveground because many perennial plants persist belowground even in the temporary absence of aboveground shoots, and because the roots and rhizomes of plant individuals occupy larger areas than do shoots. Consequently, the species-area relationship may show steeper slopes for below- than aboveground richness. Further, the ratio of below: aboveground richness may vary along environmental gradients of productivity, disturbance and heterogeneity, so aboveground richness may not be a constant proportion of belowground richness. Differences in the way plants interact with storable belowground resources supplied in three dimensions (i. e. water and nutrients) and non-storable aboveground resources supplied in one-dimension (i.e. light) may allow belowground richness to continue to increase with increasing habitat productivity even while aboveground richness decreases. In summary, current DNA-based methods are likely to reveal patterns different from those well-documented for aboveground richness and may also produce new insights about plant community structure and function.

Image caption: Plant richness is greater below- than aboveground because many perennial plants persist belowground even in the temporary absence of aboveground shoots, and because the roots and rhizomes of plant individuals occupy larger areas than do shoots. Coutresy of Meelis Pärtel.

 

Conspicuous eggshell colour varies more between females than between diets

Donald Dearborn, Daniel Hanley, Katherine Ballantine, John Cullum and DeeAnn Reeder

The eggs of many birds, such as the blotched eggs of a plover or the brown-spotted eggs of a sparrow, are camouflaged against predators. But some birds lay eggs that seem startlingly conspicuous, such as the bright blue eggs of American robins. Why should these conspicuous eggs exist, when predators pose a large risk to the nest success of most birds? One possible explanation is that the bright colour of blue-green eggs can tell a male bird something about the quality of his mate. The male could use this information to decide how much parental investment to make in those eggs, versus saving energy for the next breeding attempt with perhaps a better partner.

The blue-green pigment in birds' eggs is derived from an antioxidant in the mother. Consequently, an intense blue-green eggshell colour could indicate that the mother is in good health and has antioxidants to spare. In contrast, if a female has a weak antioxidant system, she could not afford to deposit high levels of blue-green pigment into her eggshells. Under this hypothesis, there is disagreement about whether egg colour - and thus a female's antioxidant capacity - is determined mainly by recent dietary intake of antioxidants or by more permanent differences between females (such as genetics).

We tested these explanations for egg-colour variation by manipulating the diet of captive-reared Araucana chickens that lay blue-green eggs. In our experiment, each bird laid eggs during two diet treatments differing in whether they were supplemented with high levels of antioxidants, much like giving birds a daily vitamin. Somewhat surprisingly, the diet treatment had only a small effect on eggshell colour, but individual females differed strongly and consistently from one another in the colour of their eggshells, despite having been reared under identical conditions. This means that intrinsic differences between females - much more so than diet - led to differences in eggshell colouration. However, analysis of the avian visual system predicts that almost all of these egg-colour differences between females are unlikely to be seen by male birds. In other words, the signal of female quality may not be strong enough for males to actually detect.

Image caption: Variation in Araucana eggshell colouration. Coutresy of Katherine Ballantine.

 

Behavioural compensation reduces energy expenditure during migration hyperphagia in a large bird

Magella Guillemette, Samantha E. Richman, Steven J. Portugal and Patrick J. Butler

Bird migration is often seen as the summit of animal performance but it is difficult to monitor, owing to the mobility of birds. Because there must be a limit to the amount of energy that can be consumed or expended, we test the general idea that such a limit is reached during migration for eider ducks, a large bird diving for food and spending energy at a high rate while flying. We use heart rate data loggers that make it possible to study energy expenditure and behaviour before, during and after migration in an integrative manner.

When comparing periods before and after migration we found that daily energy expenditure does not vary substantially. This result is obtained despite a large increase in foraging effort observed before departure, which biologists call migration hyperphagia (an obligatory period during which migratory birds build body reserves by foraging and feeding intensely). The result is counterintuitive and analogous somehow to a man running for a long time without an increase in energy expenditure at the end of the day.

We were able to elucidate this intriguing feat by monitoring exactly how much time and energy common eider spent foraging, flying and being inactive. We showed that the large increase in energy expenditure associated with hyperphagia was completely counteracted by a decrease in energy expenditure while inactive, suggesting both a shift from high cost behaviour ('comfort' activities such as stretching, cleaning, preening and washing) to low cost behaviour (resting), and by a reduction in time spent flying before migration. Thus, by reducing energy expenditure during the part of their time not spent foraging, migrating birds may circumvent the important cost associated with hyperphagia. Finally, we hypothesised that such a mechanism of energy saving is used by other migratory birds.

Image caption: Common eiders Somateria mollissima in flight. Because of their short pointed wings and high wing-loadings, flight costs and flight speed are high in this species. Coutresy of Peter Lyngs.

 

Mother knows best - or does she?!

Suvi Ruuskanen , Blandine Doligez , Natalia Pitala , Lars Gustafsson and Toni Laaksonen

For humans as well as many other animals the conditions and resources mothers provide for offspring during growth (such as nutrition, exposure to various chemicals or hormones) may have long-lasting consequences on life, affecting for example size as adults, disease resistance and reproduction. These are so-called maternal effects. Via maternal effect mothers may adapt offspring to the environment they will face and thus increase their chances of surviving. In birds, mothers may affect the characteristics of their offspring even before chicks have hatched via transferring variable amounts of hormones in the eggs. Exposure to hormones in early life is known to affect chick growth and disease resistance, and may have long-lasting consequences on breeding and survival, but these effects are poorly known in wild birds.

In this study we increased the amount of androgen hormones (incl. testosterone) in eggs of a small passerine bird, the collared flycatcher, in our study population in Gotland, Sweden. Control eggs were injected with oil only. We then followed offspring from these nests in the next two breeding seasons: we monitored if they survived to breed and the number of eggs laid and number of chicks raised. More eggs or chicks mean of course better success. We found that males originating from eggs with high androgen levels were less likely to return to breed, i.e. to survive, than control males, but androgens had no effect on female offspring. Breeding success was not different in androgen-treated and control groups in either females or males.

We also studied if mothers or fathers of androgen-treated nests would suffer from raising these potentially more needy chicks. Lower survival or breeding success of parents the next year would reveal if such cost occurred. We however did not find any negative effects on parents.

To sum up, exposure to high levels of hormones in early life is detrimental for male offspring but not female offspring nor parents in our study species. This may constrain the allocation of hormones to eggs or potentially select mothers to allocate different amounts of hormones to eggs of sons and daughters.

Image caption: Male collared flycatcher Ficedula albicollis. Coutresy of Päivi Sirkiä.

 

Is honesty the best policy? Testing signal reliability in fiddler crabs when receiver-dependent costs are high

Robbie Wilson and Candice Bywater

In many species, males fight to establish rights to food, shelter or females. As combat risks injury or even death, individuals may signal their underlying strength to others, eliminating the need for physical battle. Signals may be behavioural, as in growling or posturing, but are often structural - including the antlers of deer, and the enlarged fore-claw of many crustaceans. A male that overstates his quality could improve his ability to gain food or mates, but surprisingly, most signals are honest reflections of a male's prowess. In fact, the chance of exposure and punishment is thought to play a key role in keeping animals honest. Males with signals that make them appear better, or stronger, than they really are might win some disputes, but they risk exposure as 'weak' and severe punishment by competitors. We tested the idea that the likelihood of being exposed as dishonest - as well as the potential severity of punishment - would affect the prevalence of honesty versus dishonesty in a population. To answer this question, we examined wild populations of male fiddler crabs in Queensland, Australia, which use an enlarged claw to signal underlying strength; however, some males do not have the claw muscle to back up their claims of quality and so are considered 'dishonest'. We expected to find crabs living in denser populations (associated with increased risk of exposure) and where the body sizes of competitors were larger (associated with increased potential punishment) would be associated with honesty - that is, a closer link between a male's signal of strength (claw size) and his actual, underlying claw strength. Our study showed that individual crabs did in fact produce more reliable signals of strength when they lived in populations with higher overall biomass (a combined measure of population density and body size), supporting the idea that honesty in nature is maintained by costs associated with exposure and punishment. We are among the first to show a link between population-level characteristics and the signalling behaviour of individuals in nature.

Image caption: The enlarged claw of a male two-toned fiddler crab, Ucavomeris. Coutresy of Daniel Hancox.

 

Elucidating the temperature response of survivorship in insects

Priyanga Amarasekare and Romina Sifuentes

The survival of cold-blooded animals (ectotherms), e.g., insects, fish, frogs and lizards, depends on environmental temperature. Mounting evidence for climate warming makes it important that we identify which ectotherm species are most at risk of extinction due to warming. In order to predict which species' survival is most impacted by climate warming, we have first to understand how survivorship responds to temperature variation. Temperature effects on survival are well-studied in insects, but these studies present a puzzle. In some species, survivorship is unaffected by temperature except at very low or very high temperatures; these species exhibit a flat-topped or inverted U-shaped temperature response. In other species, survivorship peaks at low or high temperatures and declines as temperatures increase or decrease; these species show a left- or right-skewed temperature response. While this pattern is well-documented, the mechanisms that produce it are not well-understood. Here we develop a conceptual framework to elucidate these mechanisms. We make use of the fact that overall survivorship, from egg to adult, depends on how well each life stage survives to move on to the next stage.

Our key finding is that life stages that are highly sensitive to temperature and can persist only within a narrow temperature range have a disproportionately large effect on egg-to-adult survivorship. Therefore, egg-to-adult survivorship will exhibit an inverted-U shape only if all life stages exhibit similar responses to temperature variation. When life stages are differentially sensitive to temperature, egg-to-adult survivorship should exhibit a left- or right-skewed response depending on whether the survivorship of the most sensitive stage(s) increases or decreases with increasing temperature. Tests of these predictions with data from three Hemipteran insects provide support for our framework.

The ideas we develop can be applied to any insect or other ectotherm species with complex life cycles (e.g. eggs, juveniles, adults). They have important implications for predicting which species are most at risk of extinction due to climate warming. Warm-adapted species, in which the survivorship of highly temperature-sensitive stages increases with increasing temperature, are likely to experience an increase in egg-to-adult survivorship if the mean habitat temperature were to increase, while cold- adapted species, in which the survivorship of high-sensitivity stages decreases with increasing temperature, are likely to experience a reduction in egg-to-adult survivorship . Second, species in which life stages do not differ in temperature sensitivity, but do differ in temperature tolerance, are likely to experience a decrease in egg-to- adult survivorship if the earlier stages (e.g., early larval or nymphal stages) exhibit lower tolerance of high temperatures. In general, the life stage whose survivorship is most affected by temperature will determine how severe the effects of warming would be on the persistence of a given species. Species in which the most sensitive life stage is short relative to the time scale of temperature variation (e.g. daily or seasonal) are likely to be more adversely affected by climate warming because they would be unable to avoid periods of extreme temperature that exceed the duration of critical life stages.

Image caption: Life stages of the harlequin bug (Murgantia histrionica), a Hemipteran bug from coastal southern California (top row). From left to right are eggs, the five nymphal instars and adult bugs. Coutresy of Romina Sifuentes.

 

Fattening up for a long rest: the benefits of feeding on a new plant can offset the costs of changes in seasonality

Gregory Ragland, Sheina Sim, Serra Goudarzi, Jeffrey Feder and Daniel Hahn

Insects attack every plant of economic importance, and nearly every other plant species as well. But often a single insect species attacks only one plant species, a situation termed "specialism". Specialist plant-feeding insects are incredibly diverse, and evolutionary changes that allow an insect specialist to attack a novel plant species can happen very quickly. This shift can result in speciation, the formation of a new population that does not interbreed with the original population. But only certain conditions favor a feeding shift from one plant to another, depending on multiple environmental factors, such as the nutritional similarity of the ancestral and novel food plants and whether the different food plants are available during similar times of the year.

Our study investigates the influence of these nutritional and seasonal factors on the evolutionary shift of an insect specializing on hawthorn fruit, native to North America, to domesticated apples, introduced to North America in the last 300 years. These flies lay their eggs into fruits once per year, their maggots consume the fruits (the proverbial "worm" in the apple), then they crawl out into the soil and form a dormant pupa that will not metamorphose into a fly until the following year. Apples fruit about 3 weeks earlier in the year than hawthorns, and flies that attack apples have shifted their seasonal timing so that they mate, lay eggs, eat fruits, and enter dormancy 3 weeks earlier than flies that attack hawthorns.

The warmer the temperature, the faster dormant insects burn through stored fat reserves that they need to successfully re-start their life cycle the following year. So for the apple fly, this shift in seasonality is costly; they enter dormancy earlier in the year when temperatures are warmer. And warmer winters in the future may further increase the costs of earlier dormancy. But, it turns out that maggots feeding on apples, the non-native fruit, pack on greater fat, offsetting the cost of their shift towards earlier seasonality. These results suggest that the interplay between seasonal timing and plant nutritional quality may predict the success of insect populations infesting new types of host plants.

Image caption: Female Rhagoletis pomonella shortly after ovipositing on apple. Courtesy of Sheina Sim.

 

How do different mosses affect peatland carbon cycles?

Kate Orwin and Nick Ostle

Northern peatlands are remarkable for their globally significant carbon store. Carbon builds up in peatlands because of an imbalance in the carbon cycle. The first step in this cycle is photosynthesis: plants fix carbon by using sunlight to convert carbon dioxide (CO2) into sugars that act as a source of energy and as the building blocks of leaves, stems, and roots. The second step is decomposition: dead plant matter enters the soil to be degraded by microbes and released back to the atmosphere as CO2. Because peatlands are cold and wet, decomposition is slower than photosynthesis, so carbon accumulates in the underlying peat. Different plants make different contributions to carbon cycling, by having different capacities for photosynthesis, or producing biomass that decomposes at different rates.

Peatland plants are expected to respond to human- and climate-induced changes in the environment, with some increasing and others decreasing in abundance. Understanding how different plants contribute to carbon cycling is needed to allow us to make predictions of how changes in plant species abundance will alter the balance between photosynthesis and decomposition, and so the amount of carbon stored in peatlands. Mosses make up a large proportion of plant biomass in peatlands and they are highly diverse in their characteristics, but we know remarkably little about how they contribute to peatland carbon cycling.

This study looked at how three different but common peatland mosses: waved silk moss, heath plait-moss and red bog moss (a Sphagnum moss) affect the amount of carbon going into and out of a northern peatland. Waved silk moss and heath plait moss both form mats underneath shrubs such as heather, with heath plait moss forming thicker layers. Red bog moss forms hummocks that hold lots of water. Each moss species had a different effect on photosynthesis and produced tissues that decomposed at a different rate: red bog moss had the highest rates of photosynthesis and also decomposed slowly, whereas waved silk moss had the lowest rate of photosynthesis and decomposed quickly. Taken together, our results show that any changes in the abundance of these species will affect the carbon balance of northern peatlands in the future.

Image courtesy of Kate Orwin.

 

Costs of immunity in insects: an induced immune response increases metabolic rate and decreases antimicrobial activity

Daniel Ardia, Jacob Gantz, Brent Schneider and Stephanie Strebel

Having a strong immune system clearly helps organisms survive threats from pathogens. However developing, maintaining, and using the immune system may be costly, leading to tradeoffs between energy allocated to other functions or between aspects of the immune system itself. Our current understanding of how much energy it takes to produce an immune response is still limited, especially in invertebrates. We studied how much energy is required to produce an immune response in four species of insects: a cricket, a cockroach, and two species of beetles. Our method of eliciting an immune response was to insert a small piece of monofilament in the back of each insect and then measure how many cells attacked this insult. At the same time, we measured the amount of CO2 produced, an indication of metabolic activity in insects. We found that in all four species individuals with strong immune responses had expended more energy. Interestingly, we also found that removing hemolymph, the blood-like fluid in insects, also raised energy costs considerably. This indicates that wounding, independent of any infections, increases metabolic costs. We then tested whether the response to a monofilament insult would lead to a lower response in other aspects of immunity. Decreased function in other areas might indicate that producing an immune response to one threat has negative consequences for effectiveness against other threats. We found that our monofilament challenge led to lower levels of proteins that destroy bacteria. Overall, our results show that fighting pathogens requires energy and may lead to temporarily reduced ability to fight other threats.

Image caption: A house cricket, Acheta domesticus, awaits study prior to metabolic rate sampling following immune insult. Courtesy of Daniel Ardia.

 

Long-term water addition has limited effects on plant community structure in native tallgrass prairie

Scott Collins, Sally Koerner, Jennifer Plaut, Jordan Okie, Daniel Brese, Laura Calabrese, Alejandra Carvajal and Ryan Evansen

Debate continues about how changes in precipitation might affect plant communities. Models predict that year-to-year changes in growing season precipitation will have a greater impact on plant communities than increased precipitation variability within a growing season. Yet, most manipulative experiments either vary within-season precipitation variability, or reduce total growing season precipitation. However, in the northern Great Plains, where we conducted our study, growing season precipitation is predicted to increase with climate change. We conducted a 19-year long experiment in which we used an irrigation system to increase total growing season precipitation in upland and lowland areas of a native tallgrass prairie in Kansas, USA. Frequent fires maintain tallgrass prairie vegetation in this region, but increased annual precipitation could favor invasion by shrubs and trees.

Total cover of grassland plants increased over time with irrigation in uplands and lowlands. However, the total number of plant species did not change with irrigation. This is surprising because irrigation has been shown to increase aboveground plant biomass, and species diversity tends to decline in this grassland as biomass increases. The strongest response occurred within the irrigated lowland where after seven years of irrigation one long-lived, clonal grass, switchgrass, increased dramatically in abundance and thereafter became the most abundant species in this treatment. However, big bluestem, another long-lived clonal grass, remained the dominant species in irrigated uplands and control areas. Our results suggest that increased precipitation during the growing season as a result of climate change will have limited effects on plant community composition in frequently burned tallgrass prairie. These systems are "buffered" by strong responses by tall, clonal, long-lived grasses; one of these grasses may be largely replaced by another, but the structure of the community remains unchanged.

Image caption: Photo of study site at Konza Prairie, Kansas, USA, looking along one of the irrigation transects running from upland to lowland prairie. Courtesy of Scott Collins.

 

The demographic impacts of shifts in climate means and extremes on alpine butterflies

Lauren B. Buckley and Joel G. Kingsolver

Both researchers and the public tend to focus on how organisms will respond to shifts in average weather conditions due to climate change: what ecological impacts will occur if the world warms by 3°C? Yet, the most severe impacts of climate change may be due to increases in the incidence of extreme heat events. Little is known about how shifts in average temperatures and acute thermal stress events interact to impact populations of plants and animals. We examine this interaction for sulphur butterflies at different elevations in the Rocky Mountains of Colorado, USA. Despite cooler average temperatures at higher elevations, higher elevation sites experience more variable temperatures and may thus reach warmer heat extremes than lower elevation sites. We asked whether the impacts of average and extreme temperatures vary between two species adapted to different (lower and higher) elevations. The two species differ in traits (wing coloration, body size, and fur thickness) that determine how fast they warm up in sunny conditions.

We used temperature and radiation data collected from weather stations since 1980 and a heat budget model to predict butterfly body temperatures. Both species must warm up sufficiently to fly, but they are unable to fly if they overheat. At extreme warm temperatures, the butterfly eggs die. We compared the predicted butterfly body temperatures to these temperature limits to estimate how long the butterfly could fly and how many eggs it could produce daily at each study location. Because the butterfly must fly to lay eggs, we were able to use this information to calculate how many offspring a female butterfly can produce.

We found that shifts in available flight time and egg viability since 1980 have varied between the high- and low-elevation species and elevations. At high elevations, declines in egg viability due to temperature extreme were more than offset by the increase in available flight time associated with warmer average conditions. Our study suggests that considering both average weather conditions and extreme events in addition to the traits of organisms will be important to reliably predicting the ecological impacts of climate change.

Image caption: Colias museum specimens reveal trait variation that is important to understanding responses to climate change. Courtesy of Heidi MacLean.

Search the Site

Search

Site Adverts

 
 
Virtual Issue on Evolutionary Ecology of Mutualisms Ecological Immunology Special Feature on Plant Defences