Predator Treatments Research Articles

Eumelanic Coloration Impacts Mating Behavior, Stress Response, and Predator Preference in the Polymorphic Eastern Mosquitofish

ABSTRACTThe expression of melanic or black coloration is ubiquitous and has significant behavioral and ecological relevance. Although black coloration is common, melanic morphs within populations are often considered rare. The mechanism for the maintenance of rare melanic morphs is often associated with differences in morph behavior, predator preference, or the interaction of both. Mechanistically, the genetic loci associated with black coloration in rare morphs can also influence behaviors, and these pleiotropic effects may provide some benefit to black morphs. We predicted that different mating behaviors, antipredator responses, and stress response, as well as predator preference influenced the maintenance of a rare black morph in freshwater Eastern mosquitofish. We created predator and control treatments to measure differences in melanic and silver mosquitofish behavior and cortisol levels. We also measured predator approach and attack of melanic and silver morphs. Overall, melanic morphs exhibited a higher number of mating behaviors compared to silver morphs and returned to mating attempts quicker than silver morphs after predator exposure. Melanic males also exhibited higher baseline cortisol levels, but silver males produced more cortisol after predator exposures compared to melanic males. These specific responses may provide the mechanism by which melanic males continue to persist in populations where they are rare.

Insect responses to seasonal time constraints under global change are facilitated by warming and counteracted by invasive alien predators.

In seasonal environments, organisms with complex life cycles not only contend with seasonal time constraints (TC) but also increasingly face global change stressors that may interfere with responses to TC. Here, we tested how warming and predator stress imposed during the egg and larval stages shaped life history and behavioural responses to TC in the temperate damselfly Ischnura elegans. Eggs from early and late clutches in the season were subjected to ambient and 4°C warming temperature and the presence or absence of predator cues from perch and signal crayfish. After hatching, larvae were retained at the same thermal regime, and the predator treatment was continued or not up to emergence. The late eggs decreased their development time, especially under warming and when not exposed to predator cues. However, the late eggs increased their development time when exposed to predator cues, especially to crayfish cues. The TC decreased survival of late larvae that were as eggs exposed to crayfish cues, indicating a carry-over effect. The TC and warming additively reduced late larvae development time to emergence. Independent of the TC, predator cue effects on development time were stronger during the egg than during the larval stage. The late individuals expressed lower mass at emergence, which mirrored the size difference between field-collected mothers. Warming caused a higher mass at emergence. The late individuals increased their boldness and showed a higher number of moves, whereas warming caused a decreased boldness. There was no predator cue effect on larval behaviour. The results indicate that late individuals compensate for late season egg laying, which is facilitated under warming but counteracted under predation risk, especially when imposed by the crayfish.

The hidden impact of an invasive predator: Chronic stress in common frog tadpoles

The presence of non-native predators can induce chronic stress in native species, but the physiological responses of potential prey are not well understood. We investigated the effects of the presence of a non-native predator, the red-eared slider (Trachemys scripta elegans), on common frog (Rana temporaria) tadpoles. We measured the stress hormone corticosterone (CORT) in tadpoles under two predator treatments: permanent presence and short-term presence before metamorphosis. Tadpoles without predators served as controls. The presence of a slider significantly influenced the CORT levels in tadpoles. A slider's permanent and short-term presence led to lower CORT levels compared to the control group. In addition, tadpoles from the treatment with permanent slider presence metamorphosed smaller and in shorter time.These findings suggest that tadpoles experienced chronic stress in the presence of the predator, resulting in a downregulation of the hypothalamicpituitary–nterrenal axis. Our study highlights the importance of considering the indirect effects of non-native predators on prey species, as chronic stress can have long-term effects on population dynamics and fitness. Understanding stress responses in native species can aid in effective conservation management strategies for non-native predator control.

Body size and predator cues structure variation in defensive displays of Neotropical calico snakes (Oxyrhopus spp.)

AbstractInteractions between predator and prey are fundamental drivers of ecological and evolutionary dynamics. Behavioral responses are one of the most common strategies that prey species use to deter predation, especially through highly stereotyped defensive displays. However, these displays are also predicted to show strong context‐dependence, in which individuals can dynamically employ different display elements as a function of their own characteristics (e.g., age and sex) or those of the predator (e.g., type of predator). In this study, we experimentally tested for the effects of four simulated predator cues on defensive displays in two species of South American calico snakes (genus Oxyrhopus). We found that juvenile snakes were both more likely to respond and to respond more strongly than adults and that displays were most common in response to tactile stimuli than to other treatments. However, we also found broad similarity across both simulated predator treatments and species in the components used in each snake's defensive display, suggesting a high degree of stereotyping. This research suggests an important role for both ontogeny and intensity of predation risk in structuring variation in defensive behavior in Neotropical snakes and emphasizes the foundational importance of context dependence in conceptual frameworks for understanding predator–prey interactions.

Sexually attractive traits predict predation-threat sensitivity of male alternative mating tactics

Abstract Although visual sexual signals, such as ornamental colors and courtship displays, and large body size in males are attractive to females in numerous species, they may also inadvertently attract the attention of eavesdropping predators and thus may be costly in terms of increasing individual risk of mortality to predation. Theoretically, more color ornamented and larger males should be more predation threat sensitive and suppress their sexual signaling and(or) mating effort relatively more than their less color ornamented and smaller counterparts when under predation hazard. Here, we experimentally tested this hypothesis by quantifying concurrently the rates of alternative mating tactics (courtship displays, sneak mating attempts) expressed by male Trinidadian guppies (Poecilia reticulata) varying in color ornamentation and body size under a staged immediate threat of predation. Males suppressed their overall mating effort in response to the perceived predation threat, decreasing the frequency of their (presumably more conspicuous) courtship displays significantly more on average than the frequency of their sneak mating behavior. Statistically controlling for body length, more color-ornamented males were more threat sensitive in their courtship displays, but not sneak mating attempts, under predation hazard than drabber males. Controlling for body coloration, larger males exhibited lower courtship and sneak mating efforts than smaller males in both predation treatments, but body length only influenced threat sensitivity in sneak mating behavior. These results are consistent with both the threat sensitive hypothesis and asset protection principle and highlight the phenotype dependency and adaptive plasticity of alternative mating tactics in male guppies under varying predation risk.

Trait- and density-mediated effects of predation on fecundity and fertility of Aedes aegypti (Diptera: Culicidae) mosquitoes.

Prey populations that encounter predators experience density-mediated effects through lethality and associated numerical changes in the population. Prey also exhibit trait-mediated effects through nonlethal alterations in phenotypic traits associated with exposure to predators. Immature stages of mosquitoes commonly co-occur in habitats along with predators, a natural source of mortality and potential biocontrol agent. Toxorhynchites rutilus Coquillett 1896 is a natural source of mortality with potential as a biological control agent. Previous studies have shown that predation and the mere presence of Tx. rutilus (predator cues) can alter the life-history traits of Aedes aegypti (L. 1762). In addition to observed reductions in recruitment of adults (lethality), exposure to Tx. rutilus without consumption resulted in adult Ae. aegypti females with altered growth and reduced lifespan. To determine the influence of predation on the reproductive biology of Ae. aegypti, we tested the hypothesis that predation, or exposure to predator cues, will compromise the reproduction of adult survivors through reductions in fecundity (egg batch size) and fertility (hatch rate). We observed that for both female and male Ae. aegypti, survival to adulthood was the lowest and development time the shortest in treatments containing prey removal effects, attributable to predation and treatment manipulations of density reduction. There were effects of Ae. aegypti weight, but not predation treatments, on fecundity and fertility. Results suggest that predator-mediated effects on Ae. aegypti derive from lethal effects due to consumption and alterations in other phenotypic traits of survivors, including development, weight, lifespan of adults, and population growth, but not reproductive parameters measured here.

Additive multiple predator effects increase prey mortality under experimental warming in a rocky intertidal food web

Climate warming is expected to alter species interactions, which are shaped by components of individual foraging behavior. Yet few studies examine species' behavioral responses to inform predictions about how species interactions will be affected by warming. Multiple predator effects (MPEs) may be mediated by climatic warming, especially in highly diverse coastal ecosystems that are prone to extreme warming events. In a laboratory experiment, we quantified the effects of elevated sea water temperature on mortality rates of mussels (Mytilus californianus, Conrad, 1837), and the behavioral responses of their predators: crabs (Romaleon antennarium, Stimpson, 1856) and sea stars (Pisaster ochraceus, Brandt, 1835), to understand how warming affects MPEs and if predators' behavioral responses to warming are indicative of the outcome of MPEs. Sea star effects on mussel mortality did not vary with temperature, but declined threefold in the presence of crabs, due to behavioral avoidance of physical contact with crabs. In contrast, the effect of crabs on mussel mortality was ten times higher under elevated temperature, but was unaffected by sea stars. In mixed predator treatments, crabs caused significant mussel mortality, but sea stars had weaker impacts, regardless of temperature. Consequently, multiple predators had effects that did not differ from those of the more effective crab predator. Increasing temperature in the eastern North Pacific may create locations where crabs become the dominant predator of mussels, with warming increasing predation risk for mussels in this region. Field studies should examine the effects of warming on crab predation on mussels in this system.

The effect of temperature and predation on performance in monoculture and in competition in three Daphniidae differing in body size

AbstractZooplankton body size shows a strong association with temperature, competition, and predation. Global warming affects all three drivers of body size and is thus expected to lead to substantial changes in zooplankton community composition and body size distributions. To disentangle the isolated and joint effect of temperature, competition, and fish predation on species biomass and community composition in zooplankton, we monitored population biomasses of three Daphniidae species that differ in body size (Daphnia magna, Daphnia pulex, and Ceriodaphnia reticulata) for 20 days, manipulating competition (monoculture, pairwise trials, and three‐species communities), temperature (20°C, 24°C, and 28°C) and presence or absence of fish predation. In the absence of predation, D. magna dominated in all competition experiments, even at high temperatures. D. magna went extinct, however, in the predation treatments at 24°C and 28°C. D. pulex outcompeted C. reticulata and was negatively affected by predation and high temperature. C. reticulata did not reduce biomass at high temperatures and was negatively affected by all competition trials, but was positively affected by predation. Our results indicate that the two larger‐bodied species are more negatively affected by the combination of temperature and predation than the smallest species. While higher temperatures reduced the biomass of the larger‐bodied species, it did not fundamentally change their ability to dominate over the smallest species in competition. The combined effect of warming and predation changed community composition more fundamentally, resulting in the dominance of small‐bodied species. This can have important ecosystem‐wide impacts, such as the transition to turbid, algae‐dominated systems.

FUNCTIONAL RESPONSE OF PREDATOR Paederus sp. (COLEOPTERA: STAPHYLINIDAE)

Research on predatory predation of Paederus sp. (Coleoptera: Staphylinidae) was carried out to study the functional response of the predator Paederus sp. Functional response is a form and size predictor of consumer impact on resource populations, determining the effectiveness of a predator as an agent in biological control. Predation time in hungry and not-hungry conditions influences predator-prey interactions, which are essential in functional response. The method used in predating Paederus sp. on the prey of aphids was Aphid spp. They are using four levels of prey density with two different predator treatments. The results show the functional response model of Paederus sp. predators. against the prey of Aphid spp. Described in a type II model. The level of predation of Paederus sp. showed different results for the two treatments and an increasing cystoid curve at a rising rate. The level of predation is still increasing, along with the increase in host density, and can be a starting point for controlling the Aphid spp and using predators Paederus sp. in the field.

Assessing Antipredator Behavior and the Potential to Enhance It in a Species of Conservation Concern

AbstractAnimal behavior has the potential to guide the management of populations at risk of extirpation. This includes insights into how animals respond to novel predators and whether those responses can be enhanced to improve survival. Training hatchery‐reared fish to recognize predators has been proposed as a way to reduce postrelease mortalities in the wild. Identifying the presence of innate predator recognition and the capacity for learning to recognize predators in specific species or populations can inform conservation management practices. Here, antipredator behavior (time spent moving and distance from a predator) and the efficacy of predator training were assessed for three populations of a species of conservation concern, the Arkansas Darter Etheostoma cragini, which is vulnerable to predation by esocid predators like the introduced Northern Pike Esox lucius. Arkansas Darters demonstrated some innate ability to recognize and respond to a novel esocid predator and also responded to predator cues (training), although the direction of the response to cues was opposite our prediction. Populations differed in their response to the predator treatment, highlighting the value of managing populations separately. Although the fitness consequences of exposure to predator cues remain to be tested in Arkansas Darters, our results suggest that antipredator behavior is innate and that exposure to predator cues does affect behavior; however, whether or how those behavioral changes affect survival is unclear. This study demonstrates the importance of testing enrichment practices and incorporating behavioral observations into conservation programs to guide population‐specific management decisions.

Individual response in body mass and basal metabolism to the risks of predation and starvation in passerines.

Wintering energy management in small passerines has focused on the adaptive regulation of the daily acquisition of energy reserves within a starvation-predation trade-off framework. However, the possibility that the energetic cost of living, i.e. basal metabolic rate (BMR), is being modulated as part of the management energy strategy has been largely neglected. Here, we addressed this possibility by experimentally exposing captive great tits (Parus major) during winter to two consecutive treatments of increased starvation and predation risk for each individual bird. Body mass and BMR were measured prior to and after each week-long treatment. We predicted that birds should be lighter but with a higher metabolic capacity (higher BMR) as a response to increased predation risk, and that birds should increase internal reserves while reducing their cost of living (lower BMR) when exposed to increased starvation risk. Wintering great tits kept a constant body mass independently of a week-long predation or starvation treatment. However, great tits reduced the cost of living (lower BMR) when exposed to the starvation treatment, while BMR remained unaffected by the predation treatment. Energy management in wintering small birds partly relies on BMR regulation, which challenges the current theoretical framework based on body mass regulation.

Pathogens and predators: examining the separate and combined effects of natural enemies on assemblage structure.

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.

Stress-Mediated Responses of Aedes aegypti (Diptera: Culicidae) Larvae When Exposed to Metarhizium brunneum (Hypocreales: Clavicipitaceae) and Toxorhynchites brevipalpis (Diptera: Culicidae)

Aedes aegypti mosquitoes are capable of vectoring a wide range of diseases including dengue, yellow fever, and Zika viruses, with approximately half of the worlds’ population at risk from such diseases. Development of combined predator–parasite treatments for the control of larvae consistently demonstrates increased efficacy over single-agent treatments, however, the mechanism behind the interaction remains unknown. Treatments using the natural predator Toxorhynchites brevipalpis and the entomopathogenic fungus Metarhizium brunneum were applied in the laboratory against Ae. aegypti larvae as both individual and combined treatments to determine the levels of interaction between control strategies. Parallel experiments involved the removal of larvae from test arenas at set intervals during the course of the trial to record whole body caspase and phenoloxidase activities. This was measured via luminometric assay to measure larval stress factors underlying the interactions. Combined Metarhizium and Toxorhynchites treatments were seen to drastically reduce lethal times as compared to individual treatments. This was accompanied by increased phenoloxidase and caspase activities in combination treatments after 18 h (p < 0.001). The sharp increases in caspase and phenoloxidase activities suggest that combined treatments act to increase stress factor responses in the larvae that result in rapid mortality above that of either control agent individually. This work concludes that the underlying mechanism for increased lethality in combined parasite–predator treatments may be related to additive stress factors induced within the target host larvae.

Predator Diversity Does Not Contribute to Increased Prey Risk: Evidence from a Mesocosm Study

Predation plays an important organisational role in structuring aquatic communities. Predator diversity can, however, lead to emergent effects in which the outcomes of predator–prey interactions are modified. The importance of predator diversity in regulating predator–prey interactions was investigated during a 9-day mesocosm study conducted in the middle reach of a temporarily open/closed, temperate, southern African estuary. The zooplankton community, comprising almost exclusively (&gt;95% of total counts) calanoid and cyclopoid copepods of the genera Pseudodiaptomus, Paracartia and Oithona, was subject to three different juvenile fish predator treatments at natural densities: 1. predation by Gilchristella aestuaria, (Gilchrist, 1913; SL 15.3 ± 2.4 mm); 2. predation by Myxus capensis (Valenciennes, 1836; SL 12.8 ± 3.7 mm); and 3. a combination of the two predators. The presence of the predators contributed to a significant decline in the total zooplankton abundances, with a concurrent increase in total chlorophyll-a (Chl-a) concentrations, consistent with the expectations of a trophic cascade (ANCOVA; p &lt; 0.05 in all cases). There were no significant differences in the total Chl-a concentration or total zooplankton abundances between the different predator treatments, suggesting that the increase in predator diversity did not contribute to increased prey risk or to the strength of the trophic cascade.

Trends to adaptation of the Sahara frog (Pelophylax saharicus) larvae across an environmental gradient

Species adjust their behavior and life-history to adapt to local environmental conditions. Species with a broad ecological niche often show signatures of local adaptations to different environment, particularly in extreme ones. Here, we investigate local adaptation in different populations of the North African Sahara frog (Pelophylax saharicus) living in various environmental conditions that vary mostly in temperature, precipitation, and elevation by mean of common garden experiment aiming to estimate the growth rate under two predation treatments (absence or presence of non-lethal cues of dragonfly larvae). First, we found an elevational cline in the reproductive phenology where, from low to high elevation, the reproductive season shifts to later dates, whereas that in arid environment was later than all other populations. We suggest that geographic differences in temperature and rainfall (in arid areas) explain this phenological pattern. Second, hatching success was overall high but showed a slight decline across elevation. Third, growth rate was generally faster in low and intermediate elevation populations, but slower in high elevation and arid environment populations. Populations in low and intermediate elevation responded to predation by reducing growth rate and the size at metamorphosis, but no predatory responses were recorded in high elevation and arid environment populations. Our study shows some life history signatures of local adaptation of P. saharicus in Northeast Algeria, which does not go in line with recent genetic analysis showing low population differentiation in the region.

Predation risk effects on larval development and adult life of Aedes aegypti mosquito.

Biological control is one of the methods available for control of Aedes aegypti populations. We used experimental microcosms to evaluate the effects of actual predation and predation risk by dragonfly larvae (Odonata) on larval development, adult longevity, and adult size of Ae. aegypti. We used six treatments: control, removal, variable density cues (Cues VD), fixed density cues (Cues FD), variable density predator (Predator VD), and fixed density predator (Predator FD) (n = 5 each). Predator treatments received one dragonfly larva. Cue treatments were composed of crushed Ae. aegypti larvae released into the microcosm. For the FD treatments, we maintained a larval density of 200 individuals. The average mortality of Ae. aegypti larvae in the Predator VD treatment was used as the standard mortality for the other treatments. Mosquitoes from the Predator VD and Cues VD treatments developed faster, and adults were larger and had greater longevity compared to all other treatments, likely due to the higher food availability from larval density reduction. High larval density negatively affected larval developmental time, adult size, and longevity. Males were less sensitive to density-dependent effects. Results from this study suggest that the presence of predators may lead to the emergence of adult mosquitoes with greater fitness, causing an overall positive effect on Ae. aegypti population growth rates.

Gregarious caterpillars shorten their larval development time in response to simulated predation threat

Abstract Group living in gregarious caterpillars may shorten the larval stage, which is thought to reduce predation exposure. In the gregarious caterpillar Battus polydamas archidamas (Papilionidae) we addressed the effects of simulated predation threat on the duration of the larval stage in solitary and gregarious caterpillars. We further evaluated the consequences of group rearing and predation stimuli for pupal mass. We reared caterpillars singly and in groups of ten individuals. Caterpillars were subjected to simulated predation threats (prodding with a paintbrush) and control larvae were untouched. We determined larval stage duration and pupal mass. We also recorded in solitary and gregarious caterpillars the proportion of individuals reacting to predation threats with distinct behavioural responses. Caterpillars in the group completed larval development earlier than solitary caterpillars. This pattern of accelerated development was already evident in the first instar. Simulated predation reduced the duration of both the entire larval stage and the first instar, but only for caterpillars in the group. Pupal mass was not affected by the predation treatment in either solitary or gregarious caterpillars. Solitary caterpillars showed thrashing and osmeterium display + thrashing more frequently than gregarious caterpillars, while individuals in the group reacted with osmeterium display to a greater extent. Accelerated larval development in response to predation risk has been predicted by theoretical models, but–to our knowledge–this is the first report on gregarious caterpillars. This putative adaptive response did not entail a fitness cost in terms of pupal mass.

A wolf in sheep's clothing: Predatory fish have convergent consumptive effects but divergent predation‐risk effects

AbstractAlthough consumptive effects of predators have long been central to ecology, predation‐risk effects have emerged as major components of predator–prey interactions. Both consumptive and predation‐risk effects should vary with predator functional traits (e.g., hunting mode, gape size), where consumption rates and induction of morphological and behavioral defenses correlate with prey‐specific predator threat. Ambush predators, in contrast with active predators, may face selection pressure to be cryptic to avoid detection by prey. Thus, ambush predators may change prey density through consumptive effects but have reduced or absent predation‐risk effects. We performed two mesocosm experiments with free‐roaming and caged predators to explore post‐colonization interactions of the chemically camouflaged, large‐gaped, ambush predator, pirate perch (Aphredoderus sayanus), active, large‐gaped green sunfish (Lepomis cyanellus), and active, small‐gaped golden topminnow (Fundulus chrysotus), with larval gray treefrogs (Hyla chrysoscelis) and mole salamanders (Ambystoma talpoideum). We examined the consumptive and predation‐risk effects of each predator on amphibian mortality, growth rates, tail morphology, and polyphenisms. Large‐gaped pirate perch and green sunfish had strong, equivalent consumptive effects, but only the free‐roaming active predator, green sunfish, suppressed the growth of survivors through risk‐induced trait responses. Caged green sunfish induced much stronger non‐consumptive mortality than pirate perch in gray treefrogs, an effect that was absent for mole salamanders; golden topminnows had intermediate effects. Tail defenses were a function of prey mortality and only manifested in free‐roaming predator treatments, suggesting the necessity of predator attacks or conspecific alarm signals. Likewise, mole salamander polyphenism was unaffected by caged predators, whereas free‐roaming green sunfish prevented all metamorphosis. Free‐roaming golden topminnows increased the proportion of individuals remaining as larvae, and pirate perch increased the proportion of paedomorphs and metamorphs. Overall, the prey had positively correlated anti‐predator responses across life stages, suggesting multicomponent defenses. Predator effects varied with functional traits with large‐gaped predators having strong consumptive effects, but active predators causing stronger risk‐induced changes in growth compared to cryptic ambush predators, which provides more evidence for chemical camouflage. Our results emphasize the role of hunting mode and gape size in determining consumptive and predation‐risk effects, and that predation‐risk effects cannot be reliably predicted from consumptive effects.

Lack of evidence for indirect effects from stonefly predators on primary production under future climate warming scenarios

ABSTRACT Consumptive and non-consumptive interactions of predators and prey can have strong direct and indirect effects on primary producers, such as stream algae. Increasing water temperatures may alter these interactions and thus influence productivity in streams. For each of 3 temperature treatments (‘ambient’, +2°C and +4°C), we measured the amount of algal biomass removed by grazing mayflies from 91 mesocosms after a 24-hour test period under 3 grazing treatments: lethal predators, non-lethal predators, and no predators. At all temperatures, grazers reduced algal biomass (p < 0.01), and the presence of lethal predators effectively dampened mayfly consumption of algae (p < 0.01). However, differences in algal biomass between lethal and non-lethal predator treatments were not significant, indicating that predators had no indirect behaviorally mediated effects on grazer consumption. Grazer removal of algal biomass marginally increased with increasing temperature (p = 0.051). We analyzed video data for changes in grazer foraging and drift behavior. Mayflies increased drift in the presence of lethal predators (p < 0.01) but not non-lethal predators, and no behavioral changes were seen with temperature increases. Mesocosms can help elucidate possible future shifts in trophic interactions due to climate warming. Yet, we found no evidence of indirect stonefly predator effects on grazing mayflies under these warming scenarios.

No apparent trade-off between the quality of nest-grown feathers and time spent in the nest in an aerial insectivore, the Tree Swallow

Abstract Life history theory provides a framework for understanding how trade-offs generate negative trait associations. Among nestling birds, time spent in the nest, risk of predation, and lifespan covary, but some associations are only found within species while others are only observed between species. A recent comparative study suggests that allocation trade-offs may be alleviated by disinvestment in ephemeral traits, such as nest-grown feathers, that are quickly replaced. However, direct resource allocation trade-offs cannot be inferred from interspecific trait associations without complementary intraspecific studies. Here, we asked whether there is evidence for a within-species allocation trade-off between feather quality and time spent in the nest in Tree Swallows (Tachycineta bicolor). Consistent with the idea that ephemeral traits are deprioritized, nest-grown feathers had lower barb density than adult feathers. However, despite substantial variation in fledging age among nestlings, there was no evidence for a negative association between time in the nest and feather quality. Furthermore, accounting for differences in resource availability by considering provisioning rate and a nest predation treatment did not reveal a trade-off that was masked by variation in resources. Our results are most consistent with the idea that the interspecific association between development and feather quality arises from adaptive specialization, rather than from a direct allocation trade-off.