JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Time constraints, imposed by seasonality, are common to life histories. Recent theory in evolutionary ecology predicts independent behavioral and life history responses to such constraints, but this theory remains largely untested. In our two experiments on the damselfly Lestes congener we experimentally alter individual's perception of their proximity to a time constraint and ask whether their behavior and life history respond in the directions predicted by theory. We altered larval perception of their position in the season with light regime. In one group, we hatched larvae from winter diapausing eggs in a light regime that mimics a relatively early time in the season. In the other group we hatched larvae in a light regime that mimics a late time in the season. In the late (time constrained) group, larvae would have very little time to complete development and reach a large size so that they could attain their full reproductive potential prior to winter. In the first experiment, the behaviors we assess are activity rate, which is an indicator of foraging effort and willingness to take risks, and cannibalism, which is a component of the mortality risk of foraging. As predicted, time-constrained larvae increased their activity rates, perhaps in an attempt to increase weight gain, and as a result they suffered higher rates of cannibalism. In the second experiment, we measured development rate as the rate of molting and age at maturity. As predicted, time-constrained larvae accelerated development rate and thereby matured at a significantly earlier age and smaller size. Our analysis demonstrates that the behavioral and life history responses of these larvae were independent, in the sense that the life history responses did not result from the behavioral responses.

Summary 1.Despite its prominent role in life-history theory, there is no direct empirical evidence for a behaviourally mediated predation cost of rapid growth. Moreover, we know little about how digestive physiology may also influence the shape of the growth/predation risk trade-off function. 2. We determined the role of behaviour and digestive physiology in experiments in which damselfly larvae were induced to grow slowly or rapidly by manipulating photoperiod (time stress), and exposure to a fish predator. 3. We showed that larvae under time stress grew more rapidly. Rapid-growing larvae had a higher foraging activity and a higher growth efficiency. 4. Under predation risk, larvae not only had a lower foraging activity but also a lower growth efficiency. 5. Rapid-growing larvae (i.e. those under time stress) balanced the growth/predation risk trade-off differently and took more risk in the presence of a predator, which resulted in a behaviourally mediated higher predation cost compared to slow-growing larvae. Their higher growth efficiency, however, made this cost smaller compared to a completely behaviourally mediated rapid-growth strategy. 6. Our results provide the first explicit experimental proof of a behaviourally mediated predation cost of rapid growth. Besides a behavioural coupling of growth and predation risk, resulting in the well-known trade-off, we also found a partial decoupling of these two processes by digestive physiology.

Optimal values for life history traits are expected to depend upon environmental conditions during development and the period within which development is constrained (e.g., biotic factors and time constraints, respectively). Theory predicts that life history responses to both biotic factors and time constraints may be both direct and behaviorally mediated. Few experimental studies of life histories have considered the joint effects of biotic factors and time constraints, and fewer still have been able to disentangle direct from behaviorally mediated effects. We studied such interactions by manipulating the perceived time to the onset of winter, predation risk, and food resources level in larvae of the damselfly Lestes sponsa. In the first experiment (predation ϫ time constraint), the presence of a predator caused an overall reduction in foraging activity, development rate, and mass at emergence. However, larvae that had less time available before the end of the season, increased foraging activity and development rate, while mass at emergence decreased. These results suggest that the observed changes in life history characters were behaviorally mediated in the presence of predators. In contrast, life history responses of time-constrained larvae occurred independently of the behavioral changes and, therefore, were direct. In the second experiment (food level ϫ time constraint) larvae under high food levels had a higher foraging activity, increased development rate, and higher growth rates, compared to low food-level treatments. Time-constrained larvae accelerated development and had a smaller mass at emergence at high food levels than larvae that were not time constrained. In contrast, and opposite to predictions, time-constrained larvae at low food levels had the slowest development rate and the largest mass at emergence. We suggest that larvae in the latter group were aiming to delay emergence to the next season (cohort splitting). Our results suggest that both behaviorally mediated and direct responses to biotic factors and time constraints are a feature of the life history of this damselfly.

The relationship between body size and ®tness components in odonates was examined using a meta-analysis of 33 published studies. There was a positive and signi®cant overall effect of body size on mating rate and lifetime mating success among males. There was also a weaker but still signi®cant positive effect of body size on survivorship of males. The relationship between body size, mating rate, longevity, and lifetime mating success differed signi®cantly between males of territorial and nonterritorial species. The effect of body size was signi®cant for all ®tness components in territorial species but signi®cant only for longevity and lifetime mating success in nonterritorial species. Effect sizes appeared to be strongest on longevity in both sexes, and on male mating rate in territorial species. Other effect sizes, even when signi®cant, were small. Despite a much smaller data set, female ®tness also increased signi®cantly with body size. Both clutch size and longevity showed a signi®cant positive relationship with body size. These results suggest that there is a general ®tness bene®t to large size in odonates. Nevertheless, signi®cant heterogeneity is apparent in this effect, which can be attributed to sex, mating system, and ®tness component. Finally, these analyses point to inadequacies in the current data that need further study before the potentially rich patterns in size effects on ®tness can be explored more thoroughly.

Optimal values for life history traits are expected to depend upon environmental conditions during development and the period within which development is constrained (e.g., biotic factors and time constraints, respectively). Theory predicts that life history responses to both biotic factors and time constraints may be both direct and behaviorally mediated. Few experimental studies of life histories have considered the joint effects of biotic factors and time constraints, and fewer still have been able to disentangle direct from behaviorally mediated effects. We studied such interactions by manipulating the perceived time to the onset of winter, predation risk, and food resources level in larvae of the damselfly Lestes sponsa. In the first experiment (predation × time constraint), the presence of a predator caused an overall reduction in foraging activity, development rate, and mass at emergence. However, larvae that had less time available before the end of the season, increased foraging activity and development rate, while mass at emergence decreased. These results suggest that the observed changes in life history characters were behaviorally mediated in the presence of predators. In contrast, life history responses of time‐constrained larvae occurred independently of the behavioral changes and, therefore, were direct. In the second experiment (food level × time constraint) larvae under high food levels had a higher foraging activity, increased development rate, and higher growth rates, compared to low food‐level treatments. Time‐constrained larvae accelerated development and had a smaller mass at emergence at high food levels than larvae that were not time constrained. In contrast, and opposite to predictions, time‐constrained larvae at low food levels had the slowest development rate and the largest mass at emergence. We suggest that larvae in the latter group were aiming to delay emergence to the next season (cohort splitting). Our results suggest that both behaviorally mediated and direct responses to biotic factors and time constraints are a feature of the life history of this damselfly.

Although theoretical models have identified environmental heterogeneity as a prerequisite for the evolution of adaptive plasticity, this relationship has not yet been demonstrated experimentally. Because of pool desiccation risk, adaptation of development rate is important for many amphibians. In a simulated pool‐drying experiment, we compared the development time and phenotypic plasticity in development time of populations of the common frog Rana temporaria, originating from 14 neighbouring islands off the coast of northern Sweden. Drying regime of pools used by frogs for breeding differed within and among the islands. We found that the degree of phenotypic plasticity in development time was positively correlated with the spatial variation in the pool‐drying regimes present on each island. In addition, local adaptation in development time to the mean drying rate of the pools on each island was found. Hence, our study demonstrates the connection between environmental heterogeneity and developmental plasticity at the island population level, and also highlights the importance of the interplay between local specialization and phenotypic plasticity depending on the local selection pressures.

Although, in some insect taxa, wing shape is remarkably invariant, the wings of Anisopteran dragonflies show considerable variation among genera. Because wing shape largely determines the high energetic costs of flight, it may be expected that interspecific differences are partly due to selection. In the present study, we examined the roles of long-distance migration and high-manoeuvrability mate guarding in shaping dragonfly wings, using a phylogeny-based comparative method, and geometric morphometrics to quantify wing shape. The results obtained show that migration affects the shape of both front and hind wings, and suggest that mate guarding behaviour may also have an effect, especially on the front wing. These effects on front wing shape are at least partly independent. Our findings are interesting when compared with the geographically widespread and ecologically diverse dipterans Acalyptratae (including the genus Drosophila). The wings in that group are similar in function and structure, but show strikingly low levels of interspecific variation.

Gene flow is often considered to be one of the main factors that constrains local adaptation in a heterogeneous environment.