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Latitude is known to deeply affect life with effects generalizable into ecological rules; the increasing species diversity toward tropics is the most paradigmatic. Several hypotheses tested patterns of biotic interactions' intensity along latitude. Negative interactions (i.e. competition and predation) are expected to be among the processes that produce checkerboard distribution of species. However, no relationship between checkerboardness and latitude has been uncovered. We tested Odonata assemblages worldwide for segregation patterns using a faunistic dataset (395 species arranged in 386 natural communities) spanning a wide latitudinal range (87°). We used co-occurrence analyses (C-score index and Standardized Effect Size) as an estimate of checkerboardness then correlated the occurrence of segregation to latitude. Odonata followed the Latitudinal Diversity Gradient at the regional scale (i.e. country scale) within our analyzed assemblages spanning, whereas local richness (i.e. community scale) did not follow the same pattern. Odonata assemblages structured with segregation are more common going from high to low latitudes, and local species richness have no effect on the pattern. We summarized hypotheses on how biotic interactions or ecological and historical processes can influence the spatial patterns in the checkerboards of assemblages and presented promising ways to help to gain a better mechanistic understanding of the drivers of the Latitudinal Diversity Gradient. [ABSTRACT FROM AUTHOR]

The adaptive value of correlations among phenotypic traits depends on the prevailing environmental conditions. Differences in selection pressures during species range expansions may therefore shape phenotypic integration. In this study, we assessed variation in behavioral and morphological traits, as well as their covariations, in replicated southern and northern European populations of the northward expanding dragonfly Crocothemis erythraea. Larvae from northern populations were, on average, darker in color, and therefore, better camouflaged than larvae from southern populations. However, there was no difference in activity level. Darkness and activity were positively correlated in larvae from northern populations, whereas this trait covariation was missing in southern populations. This suggests the emergence of alternative strategies in time-limited northern populations, a higher activity level that required better camouflage through darker coloration, while less active larvae benefited from an energy-saving strategy by reducing the investment in costly traits, such as body darkness. We further found that larger larvae emerged into larger adults, with a higher investment in flight morphology. Our findings imply that phenotypic integration is associated with the northward range shift, potentially differentially shaping fitness consequences, and ecological interactions in southern versus northern populations. [ABSTRACT FROM AUTHOR]

Human activities such as the application of agrochemicals may detrimentally disturb natural ecosystems, generating novel selection pressures. Here we examine how pesticides may influence community composition using the aquatic communities within bromeliad phytotelmata, and how adaptive responses to pesticides may influence community-level patterns. We first quantified the composition of macroinvertebrate communities from pesticide-free and pesticide-exposed locations. Complementary manipulative experiments where bromeliads were transplanted between pesticide-free and pesticide-exposed sites were then performed. Finally, pesticide bioassays on the most common predators (Mecistogaster modesta damselflies) and prey (Wyeomyia abebela mosquitoes) assessed a potential evolutionary mechanism that may influence community compositional differences. Our field survey revealed differences in W. abebela and M. modesta abundances between pesticide-free and pesticide-exposed areas. Our transplant experiment suggested compositional differences were not due to physical differences between bromeliads from different locations. Pesticide bioassays revealed that M. modesta from pesticide-free locations had higher innate pesticide tolerances than W. abebela from pesticide-free areas, but M. modesta larvae showed no evidence of adapted resistance as none were found where pesticides were used. Conversely, W. abebela larvae from pesticide-exposed locations had higher pesticide tolerances than individuals from pesticide-free sites, suggesting an adaptive response. This evolved resistance to pesticides may, therefore, allow W. abebela to colonize habitats free of the dominant predator in the system, explaining the higher W. abebela abundances in pesticide-exposed areas than in pesticide-free locations. We suggest that the total effect of novel stressors is driven by interactions between ecological and evolutionary processes. [ABSTRACT FROM AUTHOR]

Warming due to climate change is expected to alter species interactions. These interactions are shaped by components of individual behavior, particularly foraging behaviors. However, few studies consider species’ behavioral responses to warming to predict how species interactions will be affected by warming. We chose two complementary approaches to examine how climate warming may affect the behavior and interactions of aquatic intraguild predators. First, we measured behavioral responses to warming in six larval dragonfly species, expecting that feeding rate and activity would increase with temperature. Secondly, we conducted intraguild predation (IGP) trials with three species to understand how temperature affects IGP, and if species’ behavioral responses to warming are indicative of the outcome of IGP interactions. Warming increased feeding rates by 42% on average across species but had no effect on activity rate. The magnitude of change in feeding rate was positively correlated with the maximum temperatures species experience across their ranges. Lastly, warming increased rates of IGP twofold, however, species’ behavioral responses alone were not predictive of their susceptibility to become IG prey of other larvae at warmer temperatures. Our results provide evidence that IGP interactions may be greatly affected by future increases in temperature; however, activity responses to warming alone are weak predictors of the outcomes of these interactions. Future studies should consider other species’ traits when forecasting the effects of climate change on species interactions. [ABSTRACT FROM AUTHOR]

Natural enemy ecology strives to unify predator-prey and host-pathogen interactions under a common framework to gain insights into community- and ecosystem-level processes. To address this goal, ecologists need a greater emphasis on: (1) quantifying pathogen-mediated effects on community structure to enable comparisons with predator-mediated effects and (2) determining the interactive effects of combined natural enemies on communities. We conducted a mesocosm experiment to assess the individual and combined effects of predators (dragonfly larvae and adult water bugs) and a pathogen (ranavirus) on the abundance and composition of a larval amphibian assemblage. We found that our three natural enemies structured victim assemblages in unique ways, producing distinct assemblages. Additionally, we found that in combination treatments, predators mainly drove assemblage structure such that the assemblages most closely resembled their respective predator treatments. We also found that predators reduced infection prevalence in combination treatments, and that the magnitude of this effect was dependent on predator identity. Compared to virus-alone treatments, the presence of dragonflies and water bugs reduced infection prevalence by 79% and 63%, respectively. Additionally, the presence of dragonflies eliminated ranavirus infection in two species, which demonstrates the prominent role of predators in disease dynamics in this system. Overall, this work demonstrates the importance of considering natural enemies in community ecology, as each enemy can elicit a unique structural change. Additionally, this study provides a unique empirical test of the healthy herds hypothesis for multi-species assemblages and underscores the importance of advancing our understanding of multi-enemy interactions within communities., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Understanding large-scale variation in species richness in relation to area, energy, habitat heterogeneity and anthropogenic disturbance has been a major task in ecology. Ultimately, variation in species richness results from variation in individual species occupancies. We studied whether the individual species occupancy patterns are determined by the same candidate factors as total species richness. We sampled 26 boreal forest ponds for dragonflies (Odonata) and studied the effects of shoreline length, water vascular plant species density (WVPSD), availability of nutrients, intensity of forestry, amount of Sphagnum peat cover and pH on dragonfly species richness and individual dragonfly species. WVPSD and pH had a strong positive effect on species richness. Removal of six dragonfly species experiencing strongest responses to WVPSD cancelled the relationship between species richness and WVPSD. By contrast, removal of nine least observed species did not affect the relationship between WVPSD and species richness. Thus, our results showed that relatively common species responding strongly to WVPSD shaped the observed species richness pattern whereas the effect of least observed, often rare, species was negligible. Also, our results support the view that, despite of the great impact of energy on species richness at large spatial scales, habitat heterogeneity can still have an effect on species richness in smaller scales, even overriding the effects of area. [ABSTRACT FROM AUTHOR]

Activation of the immune system in insects has been shown to be costly in the laboratory setting, but experimental studies in the field are lacking. The costs of immunity in the wild may be different to those in the laboratory because animals in the wild are simultaneously subjected to a suite of selective agents. We have measured the costs of immune system activation in a wild population of the territorial damselfly Calopteryx splendens. Immune-challenged males were found to be less likely to be territorial and had lower overall survival rates than control or sham-manipulated males. Because territorial males have a higher mating success than nonterritorial males, this result suggests that immune-challenged males are also likely to suffer reduced mating success. However, the activation of the immune system as such did not increase predation risk; this occurred due to a combination of the former with a reduced territory-holding potential. As such, immune-challenged males not holding a territory were most susceptible to predation by birds. The size of the wing spots, a known sexually selected male trait, predicted territorial behaviour in control and sham-manipulated males, but not in immune-challenged males. Our data show that immune system activation can have several costs acting in unison and that ubiquitous ecological interactions, such as predation, may affect trade-offs between immunity and other life history traits. [ABSTRACT FROM AUTHOR]

Dispersal has important ecological and evolutionary consequences but is a poorly understood behaviour. We experimentally tested whether activation of the immune system affects dispersal in male damselflies, Calopteryx virgo, from three natural populations. We show that males that contained an experimentally inserted artificial pathogen, a nylon monofilament implant, had higher dispersal rates and flew further than control males, but not further than sham manipulated males. Our data suggest that dispersal may reduce the risk of further infections if immune system activation indicates high parasite infection risk in the present habitat. We, thus, suggest that parasites may play an important role in the evolution of host dispersal. [ABSTRACT FROM AUTHOR]

The growth of metacommunity ecology as a subdiscipline has increased interest in how processes at different spatial scales structure communities. However, there is still a significant knowledge gap with respect to relating the action of niche- and dispersal-assembly mechanisms to observed species distributions across gradients. Surveys of the larval dragonfly community (Odonata: Anisoptera) in 57 lakes and ponds in southeast Michigan were used to evaluate hypotheses about the processes regulating community structure in this system. We considered the roles of both niche- and dispersal-assembly processes in determining patterns of species richness and composition across a habitat gradient involving changes in the extent of habitat permanence, canopy cover, area, and top predator type. We compared observed richness patterns and species distributions in this system to patterns predicted by four general community models: species sorting related to adaptive trade-offs, a developmental constraints hypothesis, dispersal assembly, and a neutral community assemblage. Our results supported neither the developmental constraints nor the neutral-assemblage models. Observed patterns of richness and species distributions were consistent with patterns expected when adaptive tradeoffs and dispersal-assembly mechanisms affect community structure. Adaptive trade-offs appeared to be important in limiting the distributions of species which segregate across the habitat gradient. However, dispersal was important in shaping the distributions of species that utilize habitats with a broad range of hydroperiods and alternative top predator types. Our results also suggest that the relative importance of these mechanisms may change across this habitat gradient and that a metacommunity perspective which incorporates both niche- and dispersal-assembly processes is necessary to understand how communities are organized. [ABSTRACT FROM AUTHOR]

Studies in lakes show that fish and crayfish predators play an important role in determining the abundance of freshwater snails. In contrast, there are few studies of snails and their predators in shallow ponds and marshes. Ponds often lack fish and crayfish but have abundant insect populations. Here we present the results of field surveys, laboratory foraging trials, and an outdoor mesocosm experiment, testing the hypothesis that insects are important predators of pulmonate snails. In laboratory foraging trials, conducted with ten species of insects, most insect taxa consumed snails, and larval dragonflies were especially effective predators. The field surveys showed that dragonflies constitute the majority of the insect biomass in fishless ponds. More focused foraging trials evaluated the ability of the dragonflies Anax junius and Pantala hymenaea to prey upon different sizes and species of pulmonate snails ( Helisoma trivolvis, Physa acuta, and Stagnicola elodes). Anax junius consumed all three species up to the maximum size tested. Pantala hymenaea consumed snails with a shell height of 3 mm and smaller, but did not kill larger snails. P. acuta were more vulnerable to predators than were H. trivolvis or S. elodes. In the mesocosm experiment, conducted with predator treatments of A. junius, P. hymenaea, and the hemipteran Belostoma flumineum, insect predators had a pronounced negative effect on snail biomass and density. A. junius and B. flumineum reduced biomass and density to a similar degree, and both reduced biomass more than did P. hymenaea. Predators did not have a strong effect on species composition. A model suggested that A. junius and P. hymenaea have the largest effects on snail biomass in the field. Given that both pulmonate snails and dragonfly nymphs are widespread and abundant in marshes and ponds, snail assemblages in these water bodies are likely regulated in large part by odonate predation. [ABSTRACT FROM AUTHOR]

Periods of poor nutrition during early development may have negative fitness consequences in subsequent periods of ontogeny. In insects, suppression of growth and developmental rate during the larval stage are likely to affect size and timing of maturity, which in turn may lead to reduced reproductive success or survivorship. In light of these costs, individuals may achieve compensatory growth via behavioural or physiological mechanisms following food limitation. In this study, we examined the effects of a temporary period of food restriction on subsequent growth and age and size at maturity in the larval damselflyIschnura verticalis(Odonata: Coenagrionidae). We also asked whether this temporary period of reduced nutrition affected subsequent foraging behaviour under predation risk.I. verticalislarvae exposed to a temporary food shortage suffered from a reduced growth rate during this period relative to a control group that was fed ad libitum. However, increased growth rates later in development ensured that adult body size measurements (head and pronotum widths) did not differ between the treatments upon emergence. In contrast, adult dry mass did not catch up to that of the controls, indicating that the increased growth rates for size dimensions occur at the cost of similar gains in mass. Predators reduced foraging effort of larvae, but this reduction did not differ between control larvae and those previously exposed to poor nutrition. [ABSTRACT FROM AUTHOR]

We examined the effects of intraguild predation (IGP) and interference competition on an endangered dragonfly, Aeshna viridis Eversm. (Odonata: Anisoptera). A. viridis is rare in Europe due to the decrease in suitable habitats harboring the macrophyte Stratiotes aloides L. Stratiotes plants are the principal oviposition substrate for A. viridis females and protect the larvae of A. viridis from fish predation. In our study lakes A. viridis larvae are sympatric with larvae of Aeshna grandis and Aeshna juncea. The susceptibility of A. viridis larvae to IGP by similar-sized larvae of A. grandis and A. juncea was tested in a laboratory predation experiment. Microhabitat use of A. viridis and A. grandis was studied in the laboratory to determine the possible effects of interference competition on the spatial distribution of A. viridis larvae. Our results show that at least in laboratory conditions, A. viridis is susceptible to IGP and interference competition. In competition, A. grandis larvae dominated the middle and outer portion of S. aloides rosettes whereas A. viridis stayed in the inner parts. When A. grandis larvae were absent, A. viridis colonized the middle and outer parts of the rosettes. We conclude that asymmetric predation between odonate larvae of equal size can be intense, and that both IGP and interference competition affect A. viridis. Although natural habitat complexity diminishes their impact, these interactions may nevertheless influence the distribution of A. viridis in S. aloides waters and restrict its microhabitat use in S. aloides rosettes. [ABSTRACT FROM AUTHOR]

Larval damselflies resist infestation by parasitic larval mites by exhibiting behaviours such as grooming, crawling, swimming, and striking at host-seeking mites. Larval damselflies are known to increase time spent in these behaviours in the presence of mites but reduce time spent in these behaviours in the presence of fish predators. The presence of both fish and larval mites presents an obvious conflict: a larval damselfly may actively avoid parasitism by mites, thus increasing its risk of predation, or it may reduce its activity when fish are present, thus increasing its risk of parasitism. We analysed the behaviour of larval Ischnura verticalis in an experiment where we crossed presence and absence of fish with presence and absence of larval mites. Presence of mites induced a large increase in activity of larval I. verticalis but fish had no effect and there were no interpretable interactions between effects of mites and fish. Subsequent experiments indicated that larval I. verticalis in the presence of both mites and fish were more likely to be attacked and killed by fish than those exposed only to fish. The high activity level of I. verticalis larvae in the presence of both fish and mites may suggest that costs of parasitism are high, or that under field conditions it is rare for larvae to be in the immediate presence of both fish predators and potentially parasitic mites. [ABSTRACT FROM AUTHOR]

The relative importance of intraspecific, interspecific, and seasonal causes of larval mortality were investigated for aquatic larvae of the giant damselfly Megaloprepus coerulatus in Panama. These larvae live in water-filled holes in fallen and living trees, where they and three other common odonate species are the top predators. By mid wet season, M. coerulatus larvae were found in nearly half of all tree holes that harbored odonates. Although M. coerulatus were typically, but not always, eliminated from holes inhabited by larger hetero-specifics, M. coerulatus were more likely to encounter conspecifics than other odonate species. Hole with less than 11 of water rarely contained more than a single larva. In large holes where M. coerulatus was the only odonate species present, multiple larvae coexisted at a density of one larva per 1-21 of water. There the absence of 2-4 of the 5 larval size classes, despite a continuous input of eggs, suggested that cannibalism was a common cause of mortality. The size of the final instar, which determined adult body size, was correlated positively with tree hole volume for male, but not female, larvae. Experiments showed that when two larvae were placed together in 0.4-1 holes with abundant tadpole prey, the larger larva killed the smaller one. Often the larva that was killed was not eaten. Small larvae were more tolerant of each other than were pairs of medium or large larvae. Before killing occurred, the presence of larger larvae reduced the growth of smaller individuals, relative to controls. 'Obligate' killing was density-dependent. In 3.0-1 holes with ad libitum prey, conspecific killing occurred until the larval density stabilized at one larva per 1-1.5 I, similar to the density found in large holes under field conditions, For M. coerulatus, cannibalism functions to reduce the number of potential competitors for food in addition to providing nutrition. When interactions between paired larvae in small holes were experimentally prevented, competition for food reduced the growth of one or both larvae relative to controls. Holes that were watered during the dry season supported larval densities similar to those in the wet season. Thus, dry season mortality could not be attributed to a decrease in available prey. Rather, M. coerulatus larvae could not survive more than 1 month of complete drying. Because the dry season typically lasts more than 6 weeks, habitat drying is a secondary source of mortality, affecting second- or third-generation larvae that fail to emerge before tree holes dry out completely. [ABSTRACT FROM AUTHOR]

We determined the numbers of copulations and predatory attacks in swarms of Anopheles freeborni (Diptera: Culicidae), and the distribution of these events throughout the duration of the swarming period each day. On 19 evenings of observation, we recorded 2724 copulating pairs leaving swarms and 1351 dragonfly ( Pantala hymenaea and Erythemis collocata) attacks. Mating activity partially coincided with predator activity. Most copulations occurred between 10 and 20 min after the swarms formed, while predation events were most frequent during the initial 15 min of the swarm. We calculated the ratio of copulations to predatory attacks during the swarming period. This ratio was significantly higher in an area sheltered by trees than it was in the open. We suggest that physiological and ecological constraints other than predation operate on the mating system of this anopheline to affect the timing of swarm initiation and swarm site selection. [ABSTRACT FROM AUTHOR]

Based on evidence from field manipulations, several authors have recently suggested that interference competition among larval odonates reduces individual growth rates and biomass by reducing foraging rates. This study was designed to test the effects of food shortage on 'condition' (relative mass per unit head width) of larval Ischnura verticalis (Odonata: Coenagrionidae) under laboratory conditions and to use these results to estimate the degree of food shortage of larvae under naturally occurring field conditions. In the laboratory, there were marked differences in condition of larvae fed diets ranging from ad libitum feeding with worms to ad libitum feeding with Daphnia 1 day out of every 8. Condition of larvae collected from May through October from 17 different sites in southern Ontario indicated that, for most of the year, larvae had conditions similar to those fed ad libitum with Daphnia in the laboratory. There was no evidence that larval condition was related to population density. Condition of larvae in most sites during July was similar to that of larvae fed poor diets in the laboratory. It is unlikely that the low conditions were due to competition as there were no correlations with density across sites and population densities during July were at their lowest. Adult head widths showed a seasonal decline from mid June to the end of the flight season. There was no evidence that head widths were related to population density although there was some evidence that head widths of males were positively related to larval condition. My results do not support the hypothesis that competition is important in affecting foraging rates and subsequent development of larvae. Contrasts between my results and other studies may stem from difficulties with the interpretation of field experiments, that densities in my study may have been low due to fish predation, and/or that I. verticalis larvae are slow moving relative to other larvae and thus less likely to interact. [ABSTRACT FROM AUTHOR]

Dragonfly larvae (Odonata: Anisoptera) are often abundant in shallow freshwater habitats and frequently co-occur with predatory fish, but there is evidence that they are underutilized as prey. This suggests that species which successfully coexist with fish may exhibit behaviors that minimize their risk of predation. I conducted field and laboratory experiments to determine whether: 1) dragonfly larvae actively avoid fish, 2) microhabitat use and foraging success of larvae are sensitive to predation risk, and 3) vulnerability of larvae is correlated with microhabitat use. I experimentally manipulated the presence of adult bluegills ( Lepomis macrochirus) in defaunated patches of littoral substrate in a small pond to test whether colonizing dragonfly larvae would avoid patches containing fish. The two dominant anisopteran species, Tetragoneuria cynosura and Ladona deplanata (Odonata: Libellulidae), both strongly avoided colonizing patches where adult bluegills were present. Laboratory experiments examined the effects of diel period and bluegills on microhabitat use and foraging success, using Tetragoneuria, Ladona and confamilial Sympetrum semicictum, found in a nearby fishless pond. Tetragoneuria and Ladona generally occupied microhabitats offering cover, whereas Sympetrum usually occupied exposed locations. Bluegills induced increased use of cover in all three species, and use of cover also tended to be higher during the day than at night. Bluegills depressed foraging in Tetragoneuria and to a lesser extent in Ladona, but foraging in Sympetrum appeared unaffected. Other laboratory experiments indicated that Sympetrum were generally more vulnerable than Tetragoneuria or Ladona to bluegill predation, and that vulnerability was positively correlated with use of exposed microhabitats. Both fixed (generally low use of exposed microhabitats, diel microhabitat shifts) and reactive (predator avoidance, predator-sensitive microhabitat shifts) behavioral responses appear to reduce risk of predation in dragonfly larvae. Evidence indicates that vulnerability probably varies widely among species and even among instars within species, and suggests that spatial distributions of relatively vulnerable species may be limited by their inability to avoid predation. [ABSTRACT FROM AUTHOR]

Several features of dragonfly population biology suggest that population regulation occurs in the larval stage. This study was designed to determine if density-dependent interactions among larval odonates can affect survival, growth and emergence. First-instar larvae of the dragonfly Pachydiplax longipennis were raised in outdoor experimental ponds at initial densities of 38, 152, and 608 larvae · m, under two levels of food availability. Food availability was supplemented in half the pools by volumetric addition of zooplankton every other day. Pools in the low food treatment did not receive the zooplankton supplement. There was a strong negative effect of density on the mean growth rate of survivors, which included both emerging tenerals and individuals overwintering in the larval stage. A higher proportion emerged from low density than high density pools. Metamorphs from high density populations were smaller and emerged slightly later than those from low density, but the absolute number of metamorphs did not differ significantly among density treatments. Food supplementation significantly increased the proportion of overwintering larvae. There were no significant food-by-density interactions, indicating that food and density acted independently on larval population dynamics. Density-dependent mechanisms can clearly contribute to odonate population regulation, especially by controlling the number of larvae which emerge and the average age at reproduction. Population-level responses to density may be a result of interference among larvae. [ABSTRACT FROM AUTHOR]

This study focuses on ways that the size distribution of individuals influences the types and intensities of competitive interactions within a population of aquatic arthropod predators. Three field experiments and one laboratory experiment were designed to test for feeding interference, interference mortality, and dispersal effects within and between larval size classes of the primarily semivoltine dragonfly Tetragoneuria cynosura in Bays Mountain Lake. One field experiment documented the temporal pattern of colonization of large-mesh cylinders by the small, first-year-class larvae during a 30-day period; the results are consistent with passive (density-independent) colonization. A second field experiment examined the effect of large, second-year-class larvae at densities of 1 or 3 per cylinder (14 or 42 m) on colonization by small larvae; this colonization was inhibited at the high density of large larvae. In the laboratory experiment, when larvae of the two size-classes were together in the same aquarium, small larvae moved around less than when by themselves (dispersal inhibition). Thus the inhibition of colonization observed in the field may result from interference mortality, rather than from a flight response to the presence of larger conspecifics. To evaluate this interpretation, the third field experiment measured the in-situ functional response of large larvae to each other and to their small conspecific prey. Results suggest a type 1 (linear) functional response, with feeding inteference among large larvae. Moreover, the interference mortality inflicted by larger larvae on smaller conspecifics was apparently more intense on larger individuals within the small size-class. Taken together, the three field experiments and a statistical power analysis show how colonization and interference interact to determine the local density of small larvae, and why such interference effects are difficult to detect experimentally in the field. [ABSTRACT FROM AUTHOR]

An investigation of the larval dragonfly fauna associated with the plant, Sagittaria platyphylla, was conducted in a small pond. Despite the presence of several larval anisopteran species in the pond, only Pachydiplax longipennis larvae were found on Sagittaria plants. A study of the microspatial distribution of P. longipennis larvae on S. platyphylla indicated that larvae use the various regions of a plant in a highly non-random fashion. Larvae show a strong preference for the leaf axil area. A generalized predator, the bluegill sunfish ( Lepomis macrochirus), was allowed to selectively eat either of two larvae placed in various plant regions. This experiment indicated that larvae in a leaf axil area were significantly less susceptible to bluegill predation than larvae positioned in other plant regions. The microspatial distribution of starved larvae revealed that larvae with high hunger levels occupied the leaf axil area significantly less than well fed larvae, suggesting 1) larvae do not use these regions as feeding sites, and 2) high hunger levels may induce a behavioral shift in habitat use, with starved larvae forced into areas of high predation risk by the need to fulfill nutritional requirements. [ABSTRACT FROM AUTHOR]

Recent evidence suggests predators may change colonization rates of prey in nearby predator-free patches as an example of context-dependent habitat selection. Such remote predator effects can be positive when colonizers are redirected to nearby patches (habitat compression), or negative when nearby patches are avoided (risk contagion). However, it is unknown to what extent such responses are predator- and prey-specific and change with increasing distance from predator patches. We evaluated how cues of fish, backswimmers and dragonfly larvae affect habitat selection in replicated pond landscapes with predator-free patches located at increasing distances from a predator patch. We found evidence for risk contagion and compression, but spatial colonization patterns were both predator- and prey-specific. The mosquito Culex pipiens and water beetle Hydraena testacea avoided patches next to patches with dragonfly larvae (i.e. risk contagion). Predator-free patches next to patches with backswimmers were avoided only by mosquitoes. Mosquitoes preferentially colonized patches at some distance from a fish or backswimmer patch (i.e. habitat compression). Colonization patterns of beetles also suggested habitat compression, although reward contagion could not be fully excluded as an alternative explanation. Water beetles preferred the most isolated patches regardless of whether predators were present in the landscape, showing that patch position in a landscape alone affects colonization. We conclude that habitat selection can be a complex product of patch isolation and the combined effects of different local and remote cues complicate current attempts to predict the distribution of mobile organisms in landscapes., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Free-living parasite infectious stages, such as motile cercariae of trematodes (flatworms), can constitute substantial biomass within aquatic ecosystems and are frequently eaten by various consumers, potentially serving as an important source of nutrients and energy. However, quantitative data on their nutritional value (e.g., essential fatty acids [EFA]) are largely lacking. As EFA are leading indicators of nutritional quality and underpin aquatic ecosystem productivity, we performed fatty acid (FA) analysis on an aggregate of ~ 30,000 cercariae of the freshwater trematode, Ribeiroia ondatrae. Individual cercariae contained 15 ng of total FA, and considerable quantities of EFA, including eicosapentaenoic (EPA, at 0.79 ng cercaria -1 ) and docosahexaenoic (DHA, at 0.01 ng cercaria -1 ) acids. We estimated annual EFA production by R. ondatrae cercariae for a series of ponds in California to be 40.4-337.0 μg m -2  yr -1 for EPA and 0.7-6.2 μg m -2  yr -1 for DHA. To investigate viability of cercariae as prey, we also compared growth and FA profiles of dragonfly larvae (naiads of Leucorrhinia intacta) fed equivalent masses of either R. ondatrae or zooplankton (Daphnia spp.) for 5 weeks. Naiads raised on the two diets grew equally well, with no significant differences found in their EFA profiles. While zooplankton are widely recognized as a vital source of energy, and an important conduit for the movement of EFA between algae and higher trophic levels, we suggest a similar role for trematode cercariae by 'unlocking' EFA from the benthic environment, highlighting their potential importance as a nutrient source that supports animal health.

The influence of ectoparasitic water mite larvae ( Arrenurus) on the fluctuating asymmetry (FA) of forewing length and cell number in the foreweings of the damselfly Coenagrion puella has been investigated. We show a significant correlation between the FA of forewing length and the mite load. Most explanations for increases in FA implicate environmental stress combined with the inability of the genome to stabilize the phenotype. In contrast, our results demonstrate that FA could be the result of a very short-term impact during ontogenesis, due to chance parasitism. [ABSTRACT FROM AUTHOR]

Dispersal is notoriously difficult to measure, so its potential population consequences are often unknown. If dispersal is density-dependent, it can act in population regulation. Adult damselflies Enallagma boreale (Zygoptera: Coenagrionidae) raised as larvae under a range of competitive regimes were individually measured and marked. Individuals that survived to reproductive maturity were either recovered at the natal pond or had dispersed to nearby water bodies. Dispersing individuals were heavier at emergence than those returning to the natal pond to breed. Therefore, an increased probability of dispersal does not appear to be a response to poor conditions in this species. [ABSTRACT FROM AUTHOR]

Predicting how organisms respond to climate change requires that we understand the temperature dependence of fitness in relevant ecological contexts (e.g., with or without predation risk). Predation risk often induces changes to life history traits that are themselves temperature dependent. We explore how perceived predation risk and temperature interact to determine fitness (indicated by the intrinsic rate of increase, r) through changes to its underlying components (net reproductive rate, generation time, and survival) in Daphnia magna. We exposed Daphnia to predation cues from dragonfly naiads early, late, or throughout their ontogeny. Predation risk increased r differentially across temperatures and depending on the timing of exposure to predation cues. The timing of predation risk likewise altered the temperature-dependent response of T and R 0 . Daphnia at hotter temperatures responded to predation risk by increasing r through a combination of increased R 0 and decreased T that together countered an increase in mortality rate. However, only D. magna that experienced predation cues early in ontogeny showed elevated r at colder temperatures. These results highlight the fact that phenotypically plastic responses of life history traits to predation risk can be strongly temperature dependent.

Free-living parasite infectious stages, such as the cercariae of trematodes (flatworms), can represent substantial biomass in aquatic ecosystems, yet their interactions with other planktonic fauna are poorly understood. Given that cercariae are consumed by various aquatic predators, sometimes even preferentially over zooplankton, their presence may decrease predation pressure on free-living organisms within similar trophic niches by serving as alternate prey. Here, we experimentally examined how the presence of cercariae (Plagiorchis sp.) affected the population dynamics of common freshwater zooplankton (Daphnia sp.) in the presence of a predator (the larval dragonfly, Leucorrhinia intacta) known to consume both. After seeding 48 mesocosms with starting populations of Daphnia, we used four treatments (12 replicates each) representing a factorial combination of the absence/presence of both cercariae and dragonfly larvae and tracked Daphnia populations over 4 weeks. We found a significant interaction between the presence of cercariae and predators on Daphnia population size. When faced with predation pressure, Daphnia reached ~ 50% higher numbers when accompanied by cercariae than without, suggesting a "protective" effect of the latter by acting as substitute prey. Within aquatic ecosystems, an abundance of trematodes may prove advantageous for zooplankton communities that share common predators, but further studies will be needed to determine how this varies depending on the predator, trematode, and zooplankton taxa involved.