Simulated Predator Research Articles

Environmental forcing and predator consumption outweigh the nonconsumptive effects of multiple predators on oyster reefs.

The ability to predict how predators structure ecosystems has been shown to depend on identifying both consumptive effects (CEs) and nonconsumptive effects (NCEs) of predators on prey fitness. Prey populations may also be affected by interactions between multiple predators across life stages of the prey and by environmental factors such as disturbance. However, the intersection of these multiple drivers of prey dynamics has yet to be empirically evaluated. We addressed this knowledge gap using eastern oysters (Crassostrea virginica), a species known to suffer NCEs, as the focal prey. Over 4 months, we manipulated orthogonally the life stage (none, juvenile, adult, or both) at which oysters experienced simulated predation (CE) and exposure to olfactory cues of a juvenile oyster predator (crab), adult predator (conch), sequentially the crab and then the conch, or none. We replicated this experiment at three sites along an environmental gradient in a Florida (USA) estuary. For both juvenile and adult oysters, survival was reduced solely by CEs, and variation in growth was best explained by among-site variation in water flow, with a much smaller and negative effect of predator cue. Adults exposed to conch cue exhibited reduced growth (an NCE), but this effect was outweighed by a positive CE on growth: Surviving oysters grew faster at lower densities. Finally, conch cue reduced larval settlement (another NCE), but this was swamped by among-site variation in larval supply. This research highlights how strong environmental gradients and predator CEs may outweigh the influence of NCEs, even in prey known to respond to predator cues. These findings serve as a cautionary tale for the importance of evaluating NCE processes over temporal scales and across environmental gradients relevant to prey demography.

Defensive behaviour exhibited by the yellow-striped poison frog (Dendrobates truncatus) in response to simulated predation

Defensive behaviour exhibited by the yellow-striped poison frog (Dendrobates truncatus) in response to simulated predation

Never forget where you came from: Microhabitat of origin influences boldness and exploration in the hermit crab Clibanarius symmetricus (Diogenidae)

Behavioral traits can differ between individuals in a population and affect their fitness if they differentially influence survivorship in a microhabitat scale. This may occur when individuals experience different predation risks between microhabitats. In this study, we investigated boldness, exploration, and their correlation depending on the microhabitat of origin in the hermit crab Clibanarius symmetricus. Individuals of both sexes were collected from four microhabitats with different levels of predation exposure within the intertidal zone of a mangrove. We conducted experiments introducing the hermit crabs to a new standard environment and simulated predation attempts to assess exploration and boldness. Latency to re-emerge from the shell (boldness) was consistent and not affected by size, sex, or microhabitat type, but was slightly different between years. Exploration, in turn, varied only according to the microhabitat from which individuals were collected. Hermit crabs from the less risky environments explored the experimental arena for longer than individuals from the microhabitat most exposed to predators. This behavioral consistency in exploration activity can influence microhabitat choice in C. symmetricus. In addition, boldness and exploration were weakly correlated in a behavioral syndrome. Therefore, predation exposure can be a source of variation in exploration-avoidance personalities and can indirectly influence the expression of boldness in C. symmetricus. We conclude that personality traits can coevolve and have implications for habitat choice, but traditional theories of individual behavioral consistency still lack a unified theoretical background linking animal personality to niche specialization with empirical support.

Better safe than sorry: The response to a simulated predator and unfamiliar scent by the European hare

AbstractPredator presence can create a “landscape of fear,” which is defined as the spatially explicit distribution of perceived predation risk as seen by prey. Prey species can alter their behavior and space use as a response to increased predation risk, which might be traded off with energetic requirements. Thus, whether or not an anti‐predator behavior is performed might depend on the perceived risk. In this study, we investigated the behavioral and spatial response of the European hare (Lepus europaeus) toward the presence of a predator scent, using red fox (Vulpes vulpes) scat, an unfamiliar control scent (butyric acid), and a true control (no scent). We collected data on hare activity times and behavior using 50 camera trap locations and spatial data using GPS telemetry (30,481 GPS positions of 12 hares). Hares showed spatial anti‐predator behaviors within their home range, for example, the local avoidance of areas treated with scent and remaining further from field edges, in response to sympatric predator scent and partly also in response to unfamiliar butyric acid. Conversely, more costly anti‐predator behaviors, that is, increased vigilance at the expense of foraging, were only shown in response to the predator scent. Our results suggest that prey species respond flexibly toward scent cues, utilizing less costly anti‐predator behaviors independent of the perceived threat, whereas costly anti‐predator responses are only used in the presence of “real” threat. Further, our findings emphasize that a combination of camera trap and GPS data can provide detailed information on animal behavior and space use, and caution that interpretation of one data source alone might lead to incomplete conclusions.

Do female rainbow kribs choose males on the basis of their apparent aggression and boldness? A non-correlational mate choice study

Consistent between-individual differences in behaviour, known as personality differences, are heritable and have consequences for individual survival and reproductive success. Therefore, it is likely that personality differences are not just under natural but also under sexual selection. Indeed, the recently developed idea that individuals choose their mate based on its personality finds empirical support. However, most studies on mate choice based on personality traits are correlative pioneering work and there is a paucity of experimental studies that test for causality by disentangling personality measures from other, potentially correlated traits that may be important during mate choice. Here, we tested female preference for the apparent level and consistency of either male aggression (measured as mean distance of approach towards an animated opponent, manipulated by locating males at a fixed distance) or male boldness (measured as activity under a simulated predation threat, manipulated using a gradient in ambient water temperature) in a bi-parental West African cichlid, Pelvicachromis pulcher. Females could observe the apparent behaviour of paired stimulus males and were allowed to choose between the two stimulus males in a subsequent choice test. We found no direct effect of male apparent aggression/boldness on female choice, but an indirect effect such that female preference for the apparently bold male increased with increasing within-male pair contrast in their apparent level of boldness. Our results indicate females consider male boldness per se during mate choice, suggesting male boldness is sexually selected in our study species.Significance statementEver since Darwin introduced the concept of sexual selection, female choice has been studied extensively. However, the hypothesis that consistent between-individual differences in behaviour (known as personality differences) affect mate choice is relatively new. Correlative studies support this idea but provide only suggestive evidence. Here, we used behavioural manipulations in order to disentangle male behaviour from other, potentially correlated male traits, allowing us to test for causality between female choice and personality differences in male aggression and boldness (both in level and consistency of behaviour) in a bi-parental cichlid. We found no overall female preference for male apparent behaviour, but female preference for the bold-appearing male increased with increasing between-male contrast in apparent boldness. Our results indicate a causal link between female choice and male boldness. In future, behavioural manipulations using a temperature gradient could provide further valuable insights.

Rapid plastic changes in brain morphology in response to acute changes in predation pressure in juvenile Atlantic salmon (Salmo salar) and northern redbelly dace (Phoxinus eos)

Teleosts exhibit inter- and intra-specific variation in the size and shape of their brains. Interpopulation differences in gross brain morphology among numerous teleost fish species have been observed and have been partially attributed to plastic changes in response to their environment, including predation. These differences manifest themselves macroscopically, potentially because teleosts retain the capacity for active neuroproliferation into adulthood. Building on previous work, showing chronic exposure to predation can affect brain morphology, we sought to determine whether these differences manifest themselves on a time scale shown to induce phenotypically plastic behavioural changes. In separate trials, we held northern redbelly dace (Phoxinus eos (Cope, 1861) = Chrosomus eos Cope, 1861) and juvenile Atlantic salmon (Salmo salar Linnaeus, 1758) in semi-natural conditions and exposed them to conspecific skin extract as a proxy for predation risk over 2 weeks. After exposure, their brains were excised, photographed, and analyzed for size (multivariate ANOVA) and shape (Procrustes ANOVA). Despite their brief exposure to simulated predation pressure, subjects from both species developed significantly different brain morphologies. Compared with controls, the Atlantic salmon exhibited a different brain shape and smaller optic tecta, whereas the northern redbelly dace had larger brains with more developed olfactory bulbs and optic tecta. Our results highlight the rapidity with which external environment can alter patterns of growth in the brain.

Functional consequences of phenotypic variation between locally adapted populations: Swimming performance and ventilation in extremophile fish.

Natural selection drives the evolution of traits to optimize organismal performance, but optimization of one aspect of performance can influence other aspects of performance. Here, we asked how phenotypic variation between locally adapted fish populations affects locomotion and ventilation, testing for functional trade-offs and trait-performance correlations. Specifically, we investigated two populations of livebearing fish (Poecilia mexicana) that inhabit distinct habitat types (hydrogen-sulphide-rich springs and adjacent nonsulphidic streams). For each individual, we quantified different metrics of burst swimming during simulated predator attacks, steady swimming and gill ventilation. Coinciding with predictions, we documented significant population differences in all aspects of performance, with fish from sulphidic habitats exhibiting higher steady swimming performance and higher ventilation capacity, but slower burst swimming. There was a significant functional trade-off between steady and burst swimming, but not between different aspects of locomotion and ventilation. Although our findings about population differences in locomotion performance largely parallel the results from previous studies, we provide novel insights about how morphological variation might impact ventilation and ultimately oxygen acquisition. Overall, our analyses provided insights into the functional consequences of previously documented phenotypic variation, which will help to disentangle the effects of different sources of selection that may coincide along complex environmental gradients.

Model vs. playback experiments: The impact of sensory mode on predator‐specific escape responses in saki monkeys

AbstractAlthough experimentally simulating predator presence helps improve sample sizes in studies of free‐ranging animals, few studies have examined whether auditory playbacks and visual models produce similar results. Additionally, it is unclear if anti‐predator strategies are specific to predator hunting styles in understudied Neotropical pitheciid primates, limiting what we can generalize about this phenomenon across this taxonomic order. We conducted predator simulation experiments to assess whether wild Rylands' bald‐faced saki monkeys (Pithecia rylandsi) recognize predators based solely on acoustic cues, exhibit predator‐specific responses to different predator types, and vary responses to presentations in different sensory modes. In our playback experiments, sakis had weak responses to non‐predator control vocalizations compared to jaguar growls and harpy eagle shrieks. In most predator playbacks, subjects' first glance corresponded to the direction from which simulated predators would typically attack (above vs. below). However, although sakis exhibited appropriate movement responses to harpy playbacks (i.e., descending canopy), they exhibited no clear movement patterns when presented with jaguar playbacks. In contrast, jaguar model experiments consistently elicited fast approaches, mobbing‐style responses, and long alarm calling bouts. Thus, if we had relied on playbacks alone, we might have concluded that sakis have only generalized responses to terrestrial ambush predators. In fact, in all variables measured (e.g., latency, number of calls, and response duration), models of both predator species elicited stronger reactions than playbacks. Results indicate that bald‐faced sakis can identify predators based solely on vocalizations, but do not exhibit predator‐specific escape responses to terrestrial predators based on acoustic cues alone. The differential response to playbacks and models calls into question the reliability of using acoustic‐only stimuli to assess the specificity of anti‐predator behavior to predator hunting styles in some primate species.

Discrete modulation of anti-predatory and agonistic behaviors by sensory communication signals in juvenile crayfish.

We investigated how the exchange of sensory signals modulates the individual behaviors of juvenile crayfish in an anti-predatory context as well as during intraspecific agonistic encounters. We first compared crayfish housed in total sensory isolation or in pairs with access to chemical and visual cues. After 1 week of housing, we analysed their individual responses to a visual danger signal while they were foraging. We found that crayfish previously housed in pairs with exchange of sensory signals responded to a simulated predator attack predominantly with freezing behavior, whereas animals deprived of all sensory communication mostly responded by performing escape tail-flips. Next, we used the same housing conditions in between repeated fights in pairs of crayfish. Aggressive and submissive behaviors increased in subsequent fights both after total isolation and after exchange of olfactory and visual signals. Thus, unlike responses to simulated predator attacks, intraspecific agonistic behavior was not modulated by exposure to the same sensory signals. However, when we tested the effects of olfactory or visual communication independently, aggression increased dramatically after the exchange of olfactory signals, which also led to a high number of rank reversals in second fights, suggesting a destabilization of the original dominance relationship. Exposure to visual cues during the 1-week separation, however, produced the opposite effect, reducing agonistic behaviors and rank reversals. These findings demonstrate that exchange of sensory signals modulates future anti-predatory decision-making and intraspecific agonistic behaviors discretely, suggesting that the effect of these signals on shared neural circuitry is context dependent.

A Quantitative Analysis of Micrurus Coral Snakes Reveals Unexpected Variation in Stereotyped Anti-Predator Displays Within a Mimicry System.

SynopsisWarning signals in chemically defended organisms are critical components of predator–prey interactions, often requiring multiple coordinated display components for effective communication. When threatened by a predator, venomous coral snakes (genus Micrurus) display a vigorous, non-locomotory thrashing behavior that has previously been qualitatively described. Given the high contrast and colorful banding patterns of these snakes, this thrashing display is hypothesized to be a key component of a complex aposematic signal under strong stabilizing selection across species in a mimicry system. By experimentally testing snake response across simulated predator cues, we analyzed variation in the presence and expression of a thrashing display across five species of South American coral snakes. Although the major features of the thrash display were conserved across species, we found that predator cue type, snake body size, and species identity predict significant inter- and intraspecific variation in the propensity to perform a display, the duration of thrashing, and the curvature of snake bodies. We also found an interaction between curve magnitude and body location that clearly shows which parts of the display vary most across individuals and species. Our results suggest that contrary to the assumption that all Micrurus species and individuals perform the same display, a high degree of variation exists despite presumably strong selection to conserve a common signal. This quantitative behavioral characterization presents a new framework for analyzing the non-locomotory motions displayed by snakes in a broader ecological context, especially for signaling systems with complex interaction across multiple modalities.

Personality- and size-related metabolic performance in invasive round goby (Neogobius melanostomus)

Differences between individuals in behavioral type (i.e. animal personality) are ecologically and evolutionarily important because they can have significant effects on fitness components such as growth and predation risk. In the present study we are used the invasive round goby (Neogobius melanostomus) from an established population in controlled experiments to examine the relationships among personality, metabolic performance, and growth rate (inferred as size-at-age). Boldness was measured as the time to return to normal behavior after a simulated predator attack, where fish with shorter freezing times were categorized as “bold” and fish with longer times were categorized as “shy.” We show that bold fish have significantly higher standard metabolic rate (SMR) than their shy conspecifics, whereas there was no difference between personality types in their maximum metabolic rate (MMR) or aerobic scope (AS). Bold fish furthermore had a smaller size-at-age as compared to shy fish. Together this provides evidence of a metabolic underpinning of personality where the high-SMR bold fish require more resources to sustain basic life functions than their low-SMR shy conspecifics, indicating that bold round goby from established populations with high densities (and high competition for food) pay a price of reduced growth rate.

Exogenous octopamine increases antipredator aggression in scorpions (Centruroides vittatus)

In many invertebrates, the monoamine octopamine (OA) acts as a hormone and neurotransmitter, regulating “fight-or-flight” behavior and aggression. Though well-studied in some taxa (e.g., insects and crustaceans), the role of OA in arachnids is little understood, and information on any hormones within scorpions is lacking. Given its effects in most arthropods, we expected elevated levels of octopamine to increase aggressive antipredator behaviors in scorpions. We experimentally raised octopamine levels in striped bark scorpions (Centruroides vittatus (Say, 1821)) and measured changes in their behavioral responses to simulated predator attack. Elevated octopamine levels increased aggressive behaviors in C. vittatus scorpions, whereas an octopamine antagonist (phentolamine) had no effect on behavior. Overall, this study begins to extend our understanding of behavioral endocrinology to scorpions, finding general similarities with spiders. Future work promises to better elucidate the role of monoamines and other hormones in regulating scorpion behavior and their interactions with predators.

Predicting the effects of restoring linear features on woodland caribou populations

Predator-prey dynamics are increasingly being modified by the alteration of natural habitats. Such alteration has led to increased predation rates and local extirpation of woodland caribou (Rangifer tarandus caribou) in western Canada. Linear features such as roads or seismic lines (narrow corridors used for petroleum exploration that are cleared of vegetation) increase predation rates on caribou by increasing wolf (Canis lupus) movement rates and by facilitating access into caribou habitat. Linear feature restoration is therefore hypothesised to help reverse caribou declines. However, with the high financial cost to restore approximately 350,000 km of seismic lines within western Canada’s boreal forests, theoretical predictions can clarify the efficacy of such actions. We use a mathematical model based on coupled ordinary differential equations representing predator-prey dynamics to estimate equilibrium densities of caribou, moose (Alces alces) and wolves under various parameter scenarios. Changes in equilibrium density serve as a proxy for the expected effect of linear feature restoration on population densities. Our model captures dynamical feedbacks between caribou and wolf densities, and also includes moose, which are the wolf’s primary prey species. With our best estimates of parameter values, caribou density increased 2.51-fold if all linear features were restored and 1.61-fold if only seismic lines were restored. As a comparison, simulated predator reductions increased caribou densities 3.92-fold, nearly twice the total response of linear feature restoration. The effect of restoration was increased if caribou group size was smaller, yet was less pronounced if carrying capacity for ungulates was higher. By varying the parameter values and fixing population densities, our approach allowed us to partition the caribou populations’ response from restoration into the contributions of the various mechanisms and feedbacks. In particular, contrasting simulation results where wolf densities are kept fixed with those where they are free to respond to prey allowed us to disentangle the relative importance of wolf functional and numerical response. This novel approach indicates that most of the increase in caribou densities after restoration was due to reduced foraging efficiency of wolves, especially reduced habitat overlap. Overall, our results suggest that restoration could substantially benefit caribou populations, but only if all linear features are restored, which is far from realistic. Linear feature restoration alone may not lead to population recovery, and should therefore be coupled with other direct management actions to successfully recover caribou.

Ship Noise Inhibits Colour Change, Camouflage, and Anti-Predator Behaviour in Shore Crabs

The marine environment is experiencing unprecedented levels of anthropogenic noise. This is known to have adverse effects across a range of taxa, directly affecting sensory systems and behaviours. Stress caused by noise pollution may affect physiological processes that do not have obvious links to the acoustic environment. We show that noise from shipping reduces colour change and consequent camouflage in juvenile shore crabs (Carcinus maenas). Furthermore, ship noise causes maladaptive defensive responses, with crabs less likely to flee a simulated predator attack. In contrast, loud natural noises at the same intensity have none of the same negative effects. Our study shows that anthropogenic noise is likely to be more disruptive than anticipated. Its effects are not confined to species that are reliant upon auditory communication, and may be more severe than would be predicted based only on the amplitude of the sound.

Habitat degradation and predators have independent trait-mediated effects on prey

Coral reefs are degrading globally leading to a catastrophic loss of biodiversity. While shifts in the species composition of communities have been well documented associated with habitat change, the mechanisms that underlie change are often poorly understood. Our study experimentally examines the effects of coral degradation on the trait-mediated effects of predators on the morphology, behaviour and performance of a juvenile coral reef fish. Juvenile damselfish were exposed to predators or controls (omnivore or nothing) in seawater that had flowed over either live or dead-degraded coral over a 45d period. No interaction between water source and predator exposure was found. However, fish exposed to degraded water had larger false eyespots relative to the size of their true eyes, and were more active, both of which may lead to a survival advantage. Non-consumptive effects of predators on prey occurred regardless of water source and included longer and deeper bodies, large false eyespots that may distract predator strikes away from the vulnerable head region, and shorter latencies in their response to a simulated predator strike. Research underscores that phenotypic plasticity may assist fishes in coping with habitat degradation and promote greater resilience to habitat change than may otherwise be predicted.

Design and development of a robotic predator as a stimulus in conditioned place aversion for the study of the effect of ethanol and citalopram in zebrafish

Zebrafish are becoming a species of choice in psychopharmacology, laying a promising path to refined pharmacological manipulations and high-throughput behavioral phenotyping. The field of robotics has the potential to accelerate progress along this path, by offering unprecedented means for the design and development of accurate and reliable experimental stimuli. In this work, we demonstrate, for the first time, the integration of robotic predators in place conditioning experiments. We hypothesized zebrafish to be capable of forming a spatial association under a simulated predation risk. We repeatedly exposed experimental subjects to a robotic heron impacting the water surface and then evaluated their spatial avoidance within the experimental tank in a subsequent predator-free test session. To pharmacologically validate the paradigm, we tested zebrafish in drug-free conditions (control groups) or in response to three different concentrations of citalopram (30, 50, and 100 mg/L) and ethanol (0.25, 0.50, and 1.00%). Experimental data indicate that, when tested in the absence of the conditioning stimulus, zebrafish displayed a marked preference for the bottom of the test tank, that is, the farthest location from the simulated attacks by the robotic heron. This conditioned geotaxis was reduced by the administration of citalopram in a linear dose-response curve and ethanol at the low concentration. Ultimately, our data demonstrate that robotic stimuli may represent valid conditioning tools and, thereby, aid the field of zebrafish psychopharmacology.

Starvation decreases behavioral consistency in a Neotropical harvestman

Consistent inter-individual differences in behavior have been shown in several animal groups, ranging from vertebrates to invertebrates. One of the most studied personality traits in animals is boldness, which is the tendency to expose to risky situations. Theory proposes that individuals’ state (e.g., body energy) would influence the expression of personality traits. In this study, we tested if boldness levels of the harvestman Mischonyx cuspidatus (measured as duration of death feigning/freezing after simulated predator attack) differ between two different states, namely sated and food deprived. We also tested if the degree of repeatability in boldness is affected by the individual state. We found no differences in the levels of boldness expressed by M. cuspidatus when comparing between different conditions (sated and food deprived) at a population level. However, we found that individuals showed more consistency in boldness when sated relative to a food-deprived condition. Finally, we suggest new avenues for future studies addressing personality in harvestmen.

Behavior, growth, and survivorship of laboratory-reared juvenile gopher tortoises following hard release

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 40:17-29 (2019) - DOI: https://doi.org/10.3354/esr00978 Behavior, growth, and survivorship of laboratory-reared juvenile gopher tortoises following hard release Thomas A. Radzio1,*, Nicholas J. Blase1, James A. Cox2, David K. Delaney3, Michael P. O’Connor1 1Department of Biodiversity, Earth, and Environmental Science, Drexel University, Philadelphia, Pennsylvania 19104, USA 2Tall Timbers Research Station and Land Conservancy, Tallahassee, Florida 32312, USA 3United States Army Construction Engineering Research Laboratory, Champaign, Illinois 61822, USA *Corresponding author: tomradzio@hotmail.com ABSTRACT: Captive rearing represents a vital component of many conservation and research programs. However, captive animals can exhibit unnatural behaviors and experience high predation following release, which can limit reintroduction success and the inferential value of studies that use released animals. Soft-release measures (e.g. penning) can acclimate individuals and limit interactions with predators but can also require considerable resources. We reared hatchling gopher tortoises Gopherus polyphemus in the laboratory for physiology experiments and subsequently hard-released them as yearlings to assess the efficacy of this low-cost release method and to explore possible captivity effects on tortoise behavior, growth, and survivorship. Hard-released yearlings exhibited limited dispersal; most constructed burrows soon after release, and, like wild juveniles, exhibited a preference for burrowing under deadwood. Video observations at burrows indicated natural behavior, including overnighting in burrows, extensive basking directly in front of burrows, and limited time away from these important refugia. Basking tortoises responded to simulated predator approach by rapidly entering burrows, with flight initiation distances and hiding times equivalent or similar to those of wild individuals. Survivorship was comparable to that of soft-released juveniles, but growth was slightly lower than expected based on observations of wild tortoises at the site, possibly reflecting performance immediately following release. Our findings indicate that captive-reared juvenile gopher tortoises respond well to hard release and exhibit natural attributes required to thrive in the wild. Moreover, studies of released juveniles can yield valuable insights into the ecology of a life stage that is poorly understood in most chelonians. KEY WORDS: Gopherus polyphemus · Turtle · Conservation · Headstarting · Antipredatorbehavior · Thermal ecology Full text in pdf format Correction PreviousNextCite this article as: Radzio TA, Blase NJ, Cox JA, Delaney DK, O’Connor MP (2019) Behavior, growth, and survivorship of laboratory-reared juvenile gopher tortoises following hard release. Endang Species Res 40:17-29. https://doi.org/10.3354/esr00978 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 40. Online publication date: September 19, 2019 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2019 Inter-Research.

Androgen and prolactin manipulation induces changes in aggressive and nurturing behavior in a fish with male parental care

Parental care can include two general types of behavior: (1) aggressive behavior, which is used to defend offspring from predators; and (2) nurturing behavior, which is used to provide offspring with environmental conditions or resources necessary for survival. Many studies have implicated androgens in promoting aggressive behavior and prolactin in promoting nurturing behavior. We experimentally manipulated these hormones to investigate their effects on parental care behavior in bluegill (Lepomis macrochirus). Parental males, which provide sole care to the developing eggs and larvae, received an implant with an androgen (11-ketotestosterone [11-KT]), an androgen antagonist (flutamide), prolactin, a prolactin-release inhibitor (bromocriptine), or castor oil (placebo). We found that 11-KT implants led to a significant increase in the frequency of aggressive behavior directed towards a simulated brood predator, and were associated with a nearly significant decrease in the frequency of nurturing behavior directed towards the developing eggs. In contrast, prolactin implants were associated with a significant increase in the frequency of nurturing behavior, but also reduced the frequency of aggressive behavior directed towards the simulated brood predator. These results suggest a hormone-mediated mechanistic trade-off between nurturing and aggressive behavior, whereby parental males are unable to be both highly nurturing and highly aggressive.

A review of methods for quantifying spatial predator–prey overlap

AbstractBackgroundStudies that attempt to measure shifts in species distributions often consider a single species in isolation. However, understanding changes in spatial overlap between predators and their prey might provide deeper insight into how species redistribution affects food web dynamics.Predator–prey overlap metricsHere, we review a suite of 10 metrics [range overlap, area overlap, the local index of collocation (Pianka's O), Hurlbert's index, biomass‐weighted overlap, asymmetrical alpha, Schoener's D, Bhattacharyya's coefficient, the global index of collocation and the AB ratio] that describe how two species overlap in space, using concepts such as binary co‐occurrence, encounter rates, spatial niche similarity, spatial independence, geographical similarity and trophic transfer. We describe the specific ecological insights that can be gained using each overlap metric, in order to determine which is most appropriate for describing spatial predator–prey interactions for different applications.Simulation and case studyWe use simulated predator and prey distributions to demonstrate how the 10 metrics respond to variation in three types of predator–prey interactions: changing spatial overlap between predator and prey, changing predator population size and changing patterns of predator aggregation in response to prey density. We also apply these overlap metrics to a case study of a predatory fish (arrowtooth flounder, Atheresthes stomias) and its prey (juvenile walleye pollock, Gadus chalcogrammus) in the Eastern Bering Sea, AK, USA. We show how the metrics can be applied to understand spatial and temporal variation in the overlap of species distributions in this rapidly changing Arctic ecosystem.ConclusionsUsing both simulated and empirical data, we provide a roadmap for ecologists and other practitioners to select overlap metrics to describe particular aspects of spatial predator–prey interactions. We outline a range of research and management applications for which each metric may be suited.