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Warming climate impacts aquatic ectotherms by changes in individual vital rates and declines in body size, a phenomenon known as the temperature‐size rule (TSR), and indirectly through altered species interactions and environmental feedbacks. The relative importance of these effects in shaping community responses to environmental change is incompletely understood. We employ a tri‐trophic food chain model with size‐ and temperature‐dependent vital rates and species interaction strengths to explore the role of direct kinetic effects of temperature and TSR on community structure along resource productivity and temperature gradients. We find that community structure, including the propensity for sudden collapse along resource productivity and temperature gradients, is primarily driven by the direct kinetic effects of temperature on vital rates and thermal mismatches between the consumer and predator species, overshadowing the TSR‐mediated effects. Overall, our study enhances the understanding of the complex interplay between temperature, species traits and community dynamics in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Body size reduction is a universal response to warming, but its ecological consequences across biological levels, from individuals to ecosystems, remain poorly understood. Most biological processes scale with body size, and warming-induced changes in body size can therefore have important ecological consequences. To understand these consequences, we propose a unifying, hierarchical framework for the ecological impacts of intraspecific body size reductions due to thermal plasticity that explicitly builds on three key pathways: morphological constraints, bioenergetic constraints and surface-to-volume ratio. Using this framework, we synthesize key consequences of warming-induced body size reductions at multiple levels of biological organization. We outline how this trait-based framework can improve our understanding, detection and generalization of the ecological impacts of warming. [ABSTRACT FROM AUTHOR]

Species invasions are predicted to increase in frequency with global change, but quantitative predictions of how environmental filters and species traits influence the success and consequences of invasions for local communities are lacking. Here we investigate how invaders alter the structure, diversity and stability regime of simple communities across environmental gradients (habitat productivity, temperature) and community size structure. We simulate all three‐species trophic modules (apparent and exploitative competition, trophic chain and intraguild predation). We predict that invasions most often succeed in warm and productive habitats and that successful invaders include smaller competitors, intraguild predators and comparatively small top predators. This suggests that species invasions and global change may facilitate the downsizing of food webs. Furthermore, we show that successful invasions leading to species substitutions rarely alter system stability, while invasions leading to increased diversity can destabilize or stabilize community dynamics depending on the environmental conditions and invader's trophic position. [ABSTRACT FROM AUTHOR]

Body mass underpins many ecological processes at the level of individuals, populations, and communities. Often estimated in arthropods from linear morphological traits such as body length or head width, these relationships can vary even between closely related taxa. Length–mass relationships of mosquito (Diptera: Culicidae) larvae are poorly known despite the importance of this family to disease and aquatic ecology. To fill this gap, we measured ontogenetic changes in linear traits (body length, head width, and thorax width) and dry and wet masses and estimated length- and width–mass relationships in larvae of 3 culicid species inhabiting different niches: the tropical Aedes albopictus (Skuse, 1894), the temperate Culex pipiens (Linnaeus, 1758), and the snowmelt Ochlerotatus punctor (Kirby, 1837). We compared our results with published length–mass allometries of other aquatic dipteran larvae. We showed that thorax width and body length, but not head width, reliably predicted body mass for our 3 species. The length–mass allometry slopes in aquatic dipterans varied considerably between and within families but were independent of phylogeny, specimen handling, preservation techniques, and data fitting methods. Slope estimates became less precise with decreasing sample size and size range. To obtain reliable estimates of the allometric slopes, we have thus recommended using data on all larval stages for intraspecific allometries and a wide range of species for interspecific allometries. We also cautioned against the indiscriminate use of length–mass allometries obtained for other taxa or collected at lower taxonomic resolutions, e.g. when using length–mass relationships to estimate biomass production at a given site. [ABSTRACT FROM AUTHOR]

Sexual size dimorphism (SSD) is caused by differences in selection pressures and life‐history trade‐offs faced by males and females. Proximate causes of SSD may involve sex‐specific mortality, energy acquisition, and energy expenditure for maintenance, reproductive tissues, and reproductive behavior. Using a quantitative, individual‐based, eco‐genetic model parameterized for North Sea plaice, we explore the importance of these mechanisms for female‐biased SSD, under which males are smaller and reach sexual maturity earlier than females (common among fish, but also arising in arthropods and mammals). We consider two mechanisms potentially serving as ultimate causes: (a) Male investments in male reproductive behavior might evolve to detract energy resources that would otherwise be available for somatic growth, and (b) diminishing returns on male reproductive investments might evolve to reduce energy acquisition. In general, both of these can bring about smaller male body sizes. We report the following findings. First, higher investments in male reproductive behavior alone cannot explain the North Sea plaice SSD. This is because such higher reproductive investments require increased energy acquisition, which would cause a delay in maturation, leading to male‐biased SSD contrary to observations. When accounting for the observed differential (lower) male mortality, maturation is postponed even further, leading to even larger males. Second, diminishing returns on male reproductive investments alone can qualitatively account for the North Sea plaice SSD, even though the quantitative match is imperfect. Third, both mechanisms can be reconciled with, and thus provide a mechanistic basis for, the previously advanced Ghiselin–Reiss hypothesis, according to which smaller males will evolve if their reproductive success is dominated by scramble competition for fertilizing females, as males would consequently invest more in reproduction than growth, potentially implying lower survival rates, and thus relaxing male–male competition. Fourth, a good quantitative fit with the North Sea plaice SSD is achieved by combining both mechanisms while accounting for sex‐specific costs males incur during their spawning season. Fifth, evolution caused by fishing is likely to have modified the North Sea plaice SSD. [ABSTRACT FROM AUTHOR]

The assessment of ecological quality in freshwater ecosystems is a key issue in many countries, but conditions for the development of assessment methodologies are often country-specific. This study proposes a simple methodology for the assessment of the ecological potential of reservoirs based on fish communities using a dataset covering major environmental and pressure gradients in reservoirs in the Czech Republic. Fish data obtained by gillnet sampling were correlated with a proxy of eutrophication as a key indicator of anthropogenic pressure for selecting appropriate fish-based indicators, establishing scoring criteria and developing the index of ecological quality. Expert judgement was also used to select potential fish indicators. Nine indicators were selected for the final fish-based index, fulfilling the criteria required by the Water Framework Directive. Two steps were used to validate the fish-based index quantification of its inter annual stability and sensitivity analysis of individual indicators. Finally, the index was compared to a previously developed general index for Central and Western Europe. Our study demonstrates that a combination of expert judgement and strict validation methods can result in an informative assessment of the ecological conditions, which can help identify conservation and restoration priorities.

1. Environmental stressors such as acidification modify community composition in freshwater habitats through their direct and indirect effects on individuals. However, the effect of acidification on various aspects of individual fitness is poorly known in aquatic insects, a key group in many freshwater habitats. 2. Here, the influence of acidification (acidity and Al toxicity), food quality and habitat properties on the reproduction of an acid‐tolerant mayfly Leptophlebia vespertina (Linnaeus, 1758) in a group of Central European lakes is explored. The focus is on last‐instar larvae as the short‐lived, semelparous adults cannot mitigate stress experienced by the larvae. 3. It is shown that the environment affects multiple determinants of individual reproductive output both directly by affecting body size and fecundity in last‐instar larvae, and indirectly by releasing the larvae from density dependence. Populations tended to be denser in more acidic sites and individuals in denser populations were substantially smaller and had lower size‐dependent fecundity and reproductive effort. All else being equal, larvae from colder sites were larger, suggesting an important role of the temperature‐size rule in this species. Size‐dependent fecundity and reproductive effort increased with better food conditions as expected, but neither reproductive measure was affected by acidity or temperature. Finally, a weak egg size‐number trade‐off with slightly smaller eggs in more fecund females was detected. 4. These results imply that indirect ecological feedbacks and food quality, rather than the direct effects of stressful environment, may dominate the effects of environmental stressors on the reproductive output of acid‐tolerant species such as L. vespertina. [ABSTRACT FROM AUTHOR]

Habitat complexity describes a wide array of spatial distribution patterns of physical structures in habitats. It affects aquatic ecosystems on multiple levels from individuals (e.g., foraging behavior) to species interactions (e.g., predation, prey selection) and entire communities (e.g., biodiversity, food web structure). We present a conceptual framework to classify these effects and use it to summarize recent advances in the field. We identify three main research gaps and limitations preventing a full synthesis of the effects of habitat complexity on aquatic communities and ecosystems. Habitat complexity is often characterized using ad hoc measures, which limits cross‐experimental comparison and meta‐analytical and modeling approaches. The effects of habitat complexity on communities and ecosystems can also involve feedback loops on lower levels of organization including the habitat complexity itself. Such ecological feedbacks can influence habitat formation and amplify or mitigate the direct effects of habitat loss and simplification or habitat restoration on populations and communities, yet are surprisingly little understood. Finally, most studies examine habitat complexity on the presence‐absence scale. This limits our ability to recognize nonlinear responses across habitat complexity gradients, which occur in many contexts in aquatic habitats. Since nonlinear responses can stabilize or destabilize population and community dynamics, we call for the use of a higher resolution of habitat complexity in future studies. We conclude that currently degraded habitats offer exciting opportunities for combining restorative efforts with research that could combine multi‐level experiments and monitoring to improve our understanding of the role of habitat complexity across aquatic ecosystems. This article is categorized under:Water and Life > Nature of Freshwater EcosystemsWater and Life > Conservation, Management, and Awareness [ABSTRACT FROM AUTHOR]

Multichannel food webs are shaped by the ability of apex predators to link asymmetric energy flows in mesohabitats differing in productivity and community traits. While body size is a fundamental trait underlying life histories and demography, its implications for structuring multichannel food webs are unexplored. To fill this gap, we develop a model that links population responses to predation, and resource availability to community‐level patterns, using a tri‐trophic food web model with two populations of intermediate consumers and a size‐selective top predator. We show that asymmetries in mesohabitat productivities and consumer body sizes drive food web structure, merging previously separate theory on apparent competition and emergent Allee effects (i.e. abrupt population collapses) of top predators. Our results yield theoretical support for empirically observed stability of asymmetric multichannel food webs and discover three novel types of emergent Allee effects involving intermediate consumers, multiple populations or multiple alternative stable states. [ABSTRACT FROM AUTHOR]

Structural complexity of habitats modifies trophic interactions by providing refuges and altering predator and prey behaviour. Nonlinear effects on trophic interaction strengths driven by these mechanisms may alter food web dynamics and community structure in response to habitat modifications. However, changes in functional response, the relationship between prey density and feeding rate, along habitat complexity (HC) gradients are little understood.We quantified functional responses along a HC gradient from an entirely unstructured to highly structured habitat in a freshwater system, using dragonfly larvae (Aeshna cyanea) preying on Chaoborus obscuripes larvae. To disentangle mechanisms by which changes in HC affect functional responses, we used two different approaches—a population‐level and a behavioural experiment—applied an information theoretic approach to identify plausible links between HC and functional response parameters, and compared our results to previous studies.Functional response shape did not change, but we found strong evidence for nonlinear dependence of attack rate and handling time on HC in our study. Combined results from both experiments imply that attack rate increased stepwise between the unstructured and structured habitats in line with the threshold hypothesis, because the predators gained better access to the prey. Handling time was lowest at an intermediate HC level in the population‐level experiment while the direct estimate of handling time did not vary with HC in the behavioural experiment. These differences point towards HC‐driven changes in foraging activity and other predator and prey behaviour.Most previous studies reported stepwise decrease in attack rate in line with the threshold hypothesis or no change with increasing HC. Moreover, changes in the handling time parameter with HC appear to be relatively common but not conforming to the threshold hypothesis. Overall, increased HC appears to, respectively, weaken and strengthen trophic links in 2D and 3D predator–prey interactions.We conclude that detailed understanding of HC effects on food webs requires complementary experimental approaches across HC gradients that consider predator foraging strategies and predator and prey behaviour. Such studies can also help guide conservation efforts as addition of structural elements is frequently used for restoration of degraded aquatic habitats. [ABSTRACT FROM AUTHOR]

Predation is a key ecological interaction affecting populations and communities. Climate warming can modify this interaction both directly by the kinetic effects of temperature on biological rates and indirectly through integrated behavioural and physiological responses of the predators and prey. Temperature dependence of predation rates can further be altered by predator‐induced plasticity of prey locomotor activity, but empirical data about this effect are lacking.We propose a general framework to understand the influence of predator‐induced developmental plasticity on behavioural thermal reaction norms in prey and their consequences for predator–prey dynamics. Using a mesocosm experiment with dragonfly larvae (predator) and newt larvae (prey), we tested if the predator‐induced plasticity alters the elevation or the slope of the thermal reaction norms for locomotor activity metrics in prey. We also estimated the joint predator–prey thermal response in mean locomotor speed, which determines prey encounter rate, and modelled the effect of both phenomena on predator–prey population dynamics.Thermal reaction norms for locomotor activity in prey were affected by predation risk cues but with minor influence on the joint predator–prey behavioural response. We found that predation risk cues significantly decreased the intercept of thermal reaction norm for total activity rate (i.e. all body movements) but not the other locomotor activity metrics in the prey, and that prey locomotor activity rate and locomotor speed increased with prey density.Temperature had opposite effects on the mean relative speed of predator and prey as individual speed increased with temperature in predators but decreased in prey. This led to a negligible effect of body temperature on predicted prey encounter rates and predator–prey dynamics. The behavioural component of predator–prey interaction varied much more between individuals than with temperature and the presence of predation risk cues in our system.We conclude that within‐population variation in locomotor activity can buffer the influence of body temperature and predation risk cues on predator–prey interactions, and further research should focus on the magnitude and sources of behavioural variation in interacting species to predict the impact of climate change on predator–prey interactions and food web dynamics. [ABSTRACT FROM AUTHOR]

Warming and predation risk are ubiquitous environmental factors that can modify life histories and population dynamics of aquatic ectotherms. While separate responses to each of these factors are well understood, their joint effects on individual life histories and population dynamics remain largely unexplored. Current theory predicts that the magnitude of prey behavioural, physiological, and life history responses to predation risk should diminish with warming due to the reduced metabolic scope. However, empirical support for this prediction remains equivocal, and experiments covering a substantial proportion of individual prey ontogeny until maturation are lacking.To fill these gaps, we ran a laboratory experiment to investigate how warming and non‐consumptive predation risk influence life history responses in the larvae of the mayfly Cloeon dipterum, an aquatic insect with highly plastic development. We reared larvae of varying initial sizes at three temperatures (21, 24, and 27°C) in a risk‐free environment and under predation risk signalled by chemical cues from dragonfly larvae (Aeshna cyanea), and followed their individual survival, growth, and development until emergence.Some C. dipterum larvae substantially prolonged their development and the proportion of these slow individuals declined rapidly with temperature and increased with predation risk. We attribute this response to cohort splitting, a common life history strategy of aquatic insects and other taxa in unpredictable environment.Growth, development, and maturation varied predictably with temperature in the fast larvae that did not prolong their development. They grew and developed faster but matured at smaller sizes with increasing temperature. Predation risk tended to slow down individual growth and development in line with the reduced metabolic scope hypothesis, but the differences were relatively minor and observable only at 21°C.Survival to subimago increased with predation risk, possibly due to indirect effects mediated by dissolved micronutrients, but did not vary significantly with temperature. Survival also tended to be higher in the slow individuals. This partly compensated for a smaller final size relative to the fast individuals and made both strategies comparable in overall fitness.Our results show that warming may erode individual‐level variability in life history responses to predation risk. This implies that warming can synchronise population dynamics and consequently make such populations more vulnerable to unpredictable disturbances. [ABSTRACT FROM AUTHOR]

Populations of the endangered diving beetle Graphoderus bilineatus are decreasing across Europe. Evidence‐based conservation of its local populations requires good knowledge of its habitat requirements, but data from different countries are often incomplete or contradictory.Graphoderus bilineatus was common until 1950s but then almost disappeared in the Czech Republic. Using data from a recent field survey in its core distributional area in the Czech Republic, we evaluate its habitat preferences at the habitat and microhabitat scale.We found that extensively managed fishponds can provide similarly suitable habitats for G. bilineatus as do more natural habitats including floodplain and sandpit pools, while the species is typically absent in intensively managed fishponds. All else being equal, the species is more likely found in larger water bodies surrounded by other wetlands and is more often absent at sites in agricultural landscape.We detected only weak preferences on the microhabitat scale. They suggested that G. bilineatus tends to occur in deeper water but closer to the shore and in microhabitats dominated by Glyceria or Typha. These microhabitat associations partly differ from those reported from other countries.Moreover, G. bilineatus was found at localities with higher species richness of large‐bodied aquatic beetles, both common and threatened, supporting the species status as an umbrella species for other aquatic macroinvertebrates.Our findings provide guidelines for conservation management of currently known localities and other potentially suitable sites, including the creation of new ones. Finally, our study reinforces the Annex II species status of G. bilineatus in the Habitats and Species Directive. [ABSTRACT FROM AUTHOR]

The spatial distribution of suitable habitats and dispersal abilities of the constituent taxa jointly affect the structure of metacommunities in standing freshwaters. Most studies exploring spatial effects on aquatic metacommunities, however, focus on at most a few taxonomic groups.Within two consecutive seasons, we studied spatial patterns in the species richness and composition of three passively dispersing and three actively flying freshwater invertebrate groups (rotifers, microcrustaceans and molluscs vs. hemipterans, aquatic beetles and odonates) in a metacommunity system consisting of 42 newly or recently created fishless pools in a highly heterogeneous Central European sandstone landscape consisting of deep valleys and steep ridges. We hypothesized that the extent to which these dispersal barriers affect invertebrate groups depends on their dispersal mode, and that the ability of each group to colonize new habitats is affected by the landscape morphology. Moreover, we predicted that the history and age of the pools would play a major role in structuring of invertebrate communities.Following the classical island biogeography pattern, habitat size (measured as pool surface area or depth) was the key characteristic influencing species richness for each of the six studied groups (range of explained variation: 10%–58.7%). The number of nearby aquatic habitats (i.e., potential colonization sources) was also an important determinant of species richness for molluscs (18.8%), crustaceans (36.4%) and aquatic beetles (27.2%). After pool size, the most important factor influencing species richness was the presence and functional composition of aquatic macrophytes in the pools, which affected the species richness of odonates (25.2%), aquatic beetles (12.2%), rotifers (11.1%), and crustaceans (8.3%).Valley distances between localities, defined as the shortest distance that avoids crossing steep ridges, explained consistently slightly more variation in species composition (2.6%–12.6%) than did Euclidean distances (1.0%–10.1%) for all six groups. Spatial variables (the valley distance matrix, position of pools within clusters in the landscape, and the number of nearby aquatic habitats) explained more variation in species composition (3.4%–25.4%) than local pool characteristics (2.8%–9.4%) or temporal variation (0%–7.6%) in all taxa except hemipterans, whose species composition was almost equally affected by local (3.3%) and spatial factors (3.4%).We conclude that landscape‐level spatial structure in our study area affects the dispersal and metacommunity assembly of both actively and passively dispersing invertebrates more than studied pool characteristics or temporal variation. The observed congruence between groups with different dispersal modes is likely because flying insects follow similar dispersal routes as the key animal vectors of passive dispersers. Our study highlights the importance of including relevant topography features in studies of aquatic metacommunities in complex and heterogeneous landscapes, even for taxa considered to be efficient dispersers. [ABSTRACT FROM AUTHOR]