Increased juvenile predation is not associated with evolved differences in adult brain size in Trinidadian killifish (Rivulus hartii)

Vertebrates exhibit extensive variation in brain size. The long‐standing assumption is that this variation is driven by ecologically mediated selection. Recent work has shown that an increase in predator‐induced mortality is associated with evolved increases and decreases in brain size. Thus, the manner in which predators induce shifts in brain size remains unclear. Increased predation early in life is a key driver of many adult traits, including life‐history and behavioral traits. Such results foreshadow a connection between age‐specific mortality and selection on adult brain size. Trinidadian killifish, Rivulus hartii, are found in sites with and without guppies, Poecilia reticulata. The densities of Rivulus drop dramatically in sites with guppies because guppies prey upon juvenile Rivulus. Previous work has shown that guppy predation is associated with the evolution of adult life‐history traits in Rivulus. In this study, we compared second‐generation laboratory‐born Rivulus from sites with and without guppies for differences in brain size and associated trade‐offs between brain size and other components of fitness. Despite the large amount of existing research on the importance of early‐life events on the evolution of adult traits, and the role of predation on both behavior and brain size, we did not find an association between the presence of guppies and evolutionary shifts in Rivulus brain size. Such results argue that increased rates of juvenile mortality may not alter selection on adult brain size.     

PHENOTYPIC DIVERSIFICATION ACROSS AN ENVIRONMENTAL GRADIENT: A ROLE FOR PREDATORS AND RESOURCE AVAILABILITY ON THE EVOLUTION OF LIFE HISTORIES

Changes in age/size‐specific mortality, due to such factors as predation, have potent evolutionary consequences. However, interactions with predators commonly impact prey growth rates and food availability and such indirect effects may also influence evolutionary change. We evaluated life‐history differences in Trinidadian killifish, Rivulus hartii, across a gradient in predation. Rivulus are located in (1) “high predation” sites with large piscivores, (2) “Rivulus/guppy” sites with guppies, and (3) “Rivulus‐only” sites with just Rivulus. Rivulus suffer higher mortality with large predators, and guppies may prey upon small/young Rivulus in Rivulus/guppy environments. In turn, population densities decline while growth rates increase in both localities compared to Rivulus‐only sites. To explore how the direct and indirect effects of predators and guppies influence trait diversification in Rivulus, we examined life‐history phenotypes across five rivers. High predation phenotypes exhibited a smaller size at reproduction, a greater number of eggs that were smaller, and increased reproductive allotment. Such changes are consistent with a direct response to predation. Rivulus from Rivulus/guppy sites were intermediate; they exhibited a smaller size at reproduction, increased fecundity, smaller eggs, and larger reproductive allotment than Rivulus‐only fish. These changes are consistent with models that incorporate the impacts of growth and resources.     

Coordinated evolution of brain size,structure, and eye size in Trinidadian killifish

Brain size, brain architecture, and eye size vary extensively in vertebrates. However, the extent to which the evolution of these components is intricately connected remains unclear. Trinidadian killifish, Anablepsoides hartii, are found in sites that differ in the presence and absence of large predatory fish. Decreased rates of predation are associated with evolutionary shifts in brain size; males from sites without predators have evolved a relatively larger brain and eye size than males from sites with predators. Here, we evaluated the extent to which the evolution of brain size, brain structure, and eye size covary in male killifish. We utilized wild‐caught and common garden‐reared specimens to determine whether specific components of the brain have evolved in response to differences in predation and to determine if there is covariation between the evolution of brain size, brain structure, and eye size. We observed consistent shifts in brain architecture in second generation common garden reared, but not wild caught preserved fish. Male killifish from sites that lack predators exhibited a significantly larger telencephalon, optic tectum, cerebellum, and dorsal medulla when compared with fish from sites with predators. We also found positive connections between the evolution of brain structure and eye size but not between overall brain size and eye size. These results provide evidence for evolutionary covariation between the components of the brain and eye size. Such results suggest that selection, directly or indirectly, acts upon specific regions of the brain, rather than overall brain size, to enhance visual capabilities.     

INFLUENCE OF THE INDIRECT EFFECTS OF GUPPIES ON LIFE‐HISTORY EVOLUTION IN RIVULUS HARTII

Early theories of life‐history evolution predict that increased predation on young/small individuals selects for delayed maturation and decreased reproductive effort, but such theory only considers changes in mortality. Predators reduce prey abundance and increase food to survivors. Theory that incorporates such indirect effects yields different predictions. Trinidadian killifish, Rivulus hartii, inhabit communities with and without guppies. Guppies prey on young Rivulus and Rivulus densities decline and growth rates increase when guppies are present. Prior work showed that Rivulus phenotypes from communities with guppies matured earlier and had higher fecundity, consistent with theories that incorporate indirect effects. Here we examined the genetic basis of these differences by rearing 2nd generation, laboratory‐born Rivulus from sites with and without guppies under two food levels that match natural differences in growth. Many locality × food interactions were significant, often reversing the relationship between communities. Such interactions imply that there are fitness trade‐offs associated with adaptation to high or low resource environments. On high food, Rivulus from localities with guppies matured earlier, produced many small eggs, and exhibited increased reproductive investment; these differences reversed on low food. Our results suggest that indirect effects mold Rivulus evolution and thereby highlight connections between community processes and evolutionary change.     

Effects of temporal patterning of predation threat on movement of a stream fish: evaluating an intermediate threat hypothesis

The addition of nocturnal, Hoplias malabaricus, and diurnal, Crenicichla alta, predatory fishes downstream of barrier waterfalls increases predation threat for a killifish, Rivulus hartii, in Trinidadian streams. We hypothesized that the diel patterning of predation risk would affect prey movement rates, and tested this hypothesis by comparing movement in river sites/zones containing both the nocturnal and diurnal predator with movement in river sites/zones containing only the nocturnal taxon. We evaluated this prediction in the framework of an intermediate threat hypothesis (ITH) that holds that movement will be highest at some intermediate level of threat. We marked prey fish in study sites in two watersheds of a river, each with waterfalls that divided the river into three zones: a predator absent zone (P0), a zone with one nocturnal predator (P1), and a zone with one nocturnal and one diurnal predator (P2), and tested the ITH prediction that movement will be ordered as P0<P1>P2. The single predator promoted longitudinal movement by Rivulus (P0<P1), while zones with the two predators retarded movement for small Rivulus (P1>P2) as predicted by the ITH. However, movement by larger, less vulnerable Rivulus remained elevated (P1=P2 or P2>P1). A displacement experiment in each zone found that threat tended to reduce the probability of a displaced fish reaching home, but the two predator zones did not differ from one another in their effect on this probability. Hence, the prediction that predator activity over the full 24 h diel cycle would retard movement, P2<P1, was not supported with respect to homing. Because habitat and predator communities change predictably from headwater streams to larger rivers in many lotic ecosystems, we present a conceptual model for predicting fish movement behavior along this continuum. The model posits an important role for predation threat, and the size and spacing of refuge patches, suggesting that human alterations of these factors will affect the natural movement of fish in streams.     

The evolution of eye size in response to increased fish predation in Daphnia

Variation in eye size is ubiquitous across taxa. Increased eye size is correlated with improved vision and increased fitness via shifts in behavior. Tests of the drivers of eye size evolution have focused on macroevolutionary studies evaluating the importance of light availability. Predator‐induced mortality has recently been identified as a potential driver of eye size variation. Here, we tested the influence of increased predation by the fish predator, the alewife (Alosa pseudoharengus) on eye size evolution in waterfleas (Daphnia ambigua) from lakes in Connecticut. We quantified the relative eye size of Daphnia from lakes with and without alewife using wild‐caught and third‐generation laboratory reared specimens. This includes comparisons between lakes where alewife are present seasonally (anadromous) or permanently (landlocked). Wild‐caught specimens did not differ in eye size across all lakes. However, third‐generation lab reared Daphnia from lakes with alewife, irrespective of the form of alewife predation, exhibited significantly larger eyes than Daphnia from lakes without alewife. This genetically based increase in eye size may enhance the ability of Daphnia to detect predators. Alternatively, such shifts in eye size may be an indirect response to Daphnia aggregating at the bottom of lakes. To test these mechanisms, we collected Daphnia as a function of depth and found that eye size differed in Daphnia found at the surface versus the bottom of the water column between anadromous alewife and no alewife lakes. However, we found no evidence of Daphnia aggregating at the bottom of lakes. Such results indicate that the evolution of a larger eye may be explained by a connection between eyes and enhanced survival. We discuss the cause of the lack of concordance in eye size variation between our phenotypic and genetic specimens and the ultimate drivers of eye size.     

LIFE-HISTORY EVOLUTION IN GUPPIES (POECILIA RETICULATA): 1. PHENOTYPIC AND GENETIC CHANGES IN AN INTRODUCTION EXPERIMENT

Previous investigations (Reznick and Endler, 1982; Reznick, 1982a, 1982b) demonstrated that genetic differences in guppy life histories were associated with differences in predation. Guppies from localities with the pike cichlid Crenicichla alta and associated predators matured earlier, had greater reproductive efforts, and produced more and smaller offspring than did guppies from localities with only Rivulus harti as a potential predator. Crenicichla preys primarily on large, sexually mature size-classes of guppies, while Rivulus preys primarily on small, immature size-classes. These patterns of predation are hypothesized to alter mean age-specific survival. Theoretical treatments of such differences in survival predict the observed trends in age at maturity and reproductive effort. We are using introduction experiments to evaluate the role of predators in selecting for these life-history patterns. The experiment whose results are presented here was conducted in a tributary to the El Cedro River (Trinidad), where a waterfall was the upstream limit to the distribution of all fish except Rivulus. Guppies collected from the Crenicichla locality immediately below the waterfall (the downstream control) were introduced over the waterfall in 1981. This introduction released the guppies from Crenicichla predation, exposed them instead to Rivulus predation only, and also introduced them to a different environment, since the introduction site has greater canopy cover than the site of origin. Changes in guppy life-history patterns can be attributed to predation and/or the environment. Evidence from fish collected and preserved in the field demonstrated that, by mid-1983, guppies from the introduction site above the waterfall matured at larger sizes and produced fewer, larger offspring. There were no consistent differences in reproductive allotment (weight of offspring/total weight). With the exception of reproductive allotment, these patterns are identical to previous comparisons between Rivulus and Crenicichla localities. A laboratory genetics experiment demonstrated that males from the introduction site matured at a later age and at a larger size than did males from the control site downstream, as predicted from the “age-specific predation” hypothesis. No differences between localities were observed for female age and size at maturity or for reproductive effort. The trends for fecundity and offspring size were the reverse of those observed in the field. Because only the males changed in the predicted fashion, it is not possible either to reject or to accept the hypothesis of age-specific predation at this time. We discuss the possible causes for these patterns and the high degree of plasticity in the life history, as evidenced by the differences in fecundity and offspring size between the field and laboratory results.     

Adaptive evolution to novel predators facilitates the evolution of damselfly species range shifts

Most species have evolved adaptations to reduce the chances of predation. In many cases, adaptations to coexist with one predator generate tradeoffs in the ability to live with other predators. Consequently, the ability to live with one predator may limit the geographic distributions of species, such that adaptive evolution to coexist with novel predators may facilitate range shifts. In a case study with Enallagma damselflies, we used a comparative phylogenetic approach to test the hypothesis that adaptive evolution to live with a novel predator facilitates range size shifts. Our results suggest that the evolution of Enallagma shifting from living in ancestral lakes with fish as top predators, to living in lakes with dragonflies as predators, may have facilitated an increase in their range sizes. This increased range size likely arose because lakes with dragonflies were widespread, but unavailable as a habitat throughout much of the evolutionary history of Enallagma because they were historically maladapted to coexist with dragonfly predators. Additionally, the traits that have evolved as defenses against dragonflies also likely enhanced damselfly dispersal abilities. While many factors underlie the evolutionary history of species ranges, these results suggest a role for the evolution of predator‐prey interactions.     

Experimental test of the influence of light availability on the evolution of eye size and behaviour in Daphnia

There exists extensive variation in eye size. Much work has provided a connection between light availability and differences in eye size across taxa. Experimental tests of the role of the light environment on the evolution of eye size are lacking. Here, we performed a selection experiment that examined the influence of light availability on shifts in eye size and the connection between eye size and phototactic (anti-predator) behaviour in Daphnia. We set-up replicate experimental populations of Daphnia, repeatedly evaluated phenotypic shifts in eye size during the ~50-day experiment, and performed a common garden experiment at the end of the experiment to test for evolutionary shifts in eye size and behaviour. Our phenotypic analyses showed that eye size rapidly diverged between the light treatments; relative eye size was consistently larger in the low versus high light treatments. Selection on eye size was also modified by variation in density as increases in Daphnia density favoured a larger eye. However, we did not observe differences in eye size between the light treatments following two generations of common garden rearing at the end of the experiment. We instead observed strong shifts in anti-predator behaviour. Daphnia from the low light treatment exhibited decreased phototactic responses to light. Our results show that decreased light relaxes selection on anti-predator behaviour. Such trends provide new insights into selection on eye size and behaviour.     

Predation Risk Avoidance by Terrestrial Amphibians: The Role of Prey Experience and Vulnerability to Native and Exotic Predators

We studied avoidance, by four amphibian prey species (Rana luteiventris, Ambystoma macrodactylum, Pseudacris regilla, Tarichia granulosa), of chemical cues associated with native garter snake (Thamnophis elegans) or exotic bullfrog (R. catesbeiana) predators. We predicted that avoidance of native predators would be most pronounced, and that prey species would differ in the intensity of their avoidance based on relative levels of vulnerability to predators in the wild. Adult R. luteiventris (presumably high vulnerability to predation) showed significant avoidance of chemical cues from both predators, A. macrodactylum (intermediate vulnerability to predation) avoided T. elegans only, while P. regilla (intermediate vulnerability to predation) and T. granulosa (low vulnerability to predation) showed no avoidance of either predator. We assessed if predator avoidance was innate and/or learned by testing responses of prey having disparate levels of prior exposure to predators. Wild‐caught (presumably predator‐exposed) post‐metamorphic juvenile R. luteiventris and P. regilla avoided T. elegans cues, while laboratory‐reared (predator‐naive) conspecifics did not; prior exposure to R. catesbeiana was not related to behavioural avoidance among adult or post‐metamorphic juvenile wild‐reared A. macrodactylum and P. regilla. These results imply that (i) some but not all species of amphibian prey avoid perceived risk from garter snake and bullfrog predators, (ii) the magnitude of this response probably differs according to prey vulnerability to predation in the wild, and (iii) avoidance tends to be largely learned rather than innate. Yet, the limited prevalence and intensity of amphibian responses to predation risk observed herein may be indicative of either a relatively weak predator–prey relationship and/or the limited importance of predator chemical cues in this particular system.     

LIFE-HISTORY EVOLUTION IN GUPPIES: 2. REPEATABILITY OF HELD OBSERVATIONS AND THE EFFECTS OF SEASON ON LIFE HISTORIES

Natural populations of guppies that co-occur with the pike cichlid Crenicichla alta and associated predators mature at smaller body sizes, produce more and smaller offspring per litter reproduce more frequently, and have higher reproductive allotments (weight of developing embryos/total body weight) than guppies that co-occur with just the killifish Rivulus harti (Reznick and Endler, 1982). I here consider three forms of repeatability in these life-history patterns: i) among replicate samples collected on the same day from the same locality, ii) between Crenicichla and Rivulus communities among a new series of localities, and iii) among a smaller series of Crenicichla and Rivulus localities sampled in two wet and two dry seasons. In the analysis of replicate collections from two localities, seven of eight statistical comparisons revealed no significant difference. The usual methodology for estimating these variables therefore accurately represents guppy life-history patterns at a given locality. Differences among guppies from Rivulus and Crenicichla localities, covering a wider geographical area than considered by Reznick and Endler (1982), were virtually identical to the previous comparison. Wet-season samples were associated with significant decreases in reproductive allotment and fecundity and significant increases in the size of mature males and the minimum size of reproducing females. Differences between guppies from Rivulus and Crenicichla localities persisted across all samples and were consistent with all other observations, although they tended to be smaller during the wet season. Discriminant analyses on female reproductive traits showed that fecundity and offspring size made strong, independent contributions to discriminating between guppies from the two types of localities. The contribution from reproductive allotment was considerably smaller. There was more overlap between predator treatments during the wet season. Only 8.5% of the individuals were misclassified during the dry season, but 19.5% were misclassified during the wet season.     

Life-history phenotypes in a live-bearing fish Brachyrhaphis episcopi living under different predator regimes: seasonal effects?

Several key life-history attributes in a tropical live-bearing fish, Brachyrhaphis episcopi, have previously been shown to differ between populations that co-occur with large predatory fish (Characin sites) and those that do not (Rivulus sites). Here we show that differences between Characin and Rivulus localities are also repeatable over time; patterns observed in the wet season also persisted during the dry. Both sexes reached maturity at a smaller size at Characin sites. Although there was no difference in fecundity between larger females living in different predator communities, smaller females at Characin sites produced more offspring. Females also produced smaller offspring at Characin localities. These differences are remarkably similar to those reported in two other species of live-bearing fish, B. rhabdophora and Poecilia reticulata suggesting possible convergent adaptation in life-history strategies due to predator-mediated effects or correlates thereof. We also found seasonal changes in life-history traits that were independent of predator community. In the wet season, mature males were larger, females allocated more to reproduction, and offspring mass was also greater. The results of our study generate testable predictions using B. episcopi to further our understanding of life-history evolution.     

Convergence of life-history phenotypes in a Trinidadian killifish (Rivulus hartii)

Convergent evolution is characterized by the independent evolution of similar phenotypes within similar selective environments. Previous work on Trinidadian killifish, Rivulus hartii, demonstrated repeatable life-history differences across communities that differ in predation intensity. These studies were performed in rivers located on the south slope of Trinidad's Northern Range Mountains. There exists a parallel series of rivers on the north slope of these mountains. As on the south slope, Rivulus is found across a gradient of fish predation. However, the predatory fish species in north-slope rivers are derived from marine families, whereas south-slope rivers contain a predatory fish fauna characteristic of the South American mainland. If predator-induced mortality and the associated indirect effects are the causal factors selecting for life-history patterns in Rivulus, and these are similar in north- and south-slope rivers, then the specific predatory species should be interchangeable and we would expect convergence of life-history phenotypes across slopes. Here, we characterize the life-history phenotypes of Rivulus from north-slope communities by measuring number of eggs, egg weight, reproductive allotment, reproductive tissue weight, and size at maturity. We find similar patterns of life-history divergence across analogous predator communities. Between slopes, minor differences in Rivulus life-history traits exist and one potential cause of these differences is the abundance of Macrobrachium prawns in north-slope rivers.     

Additive effects of predator diversity on pest control caused by few interactions among predator species

1. Studies of the impact of predator diversity on biological pest control have shown idiosyncratic results. This is often assumed to be as a result of differences among systems in the importance of predator–predator interactions such as facilitation and intraguild predation. The frequency of such interactions may be altered by prey availability and structural complexity. A direct assessment of interactions among predators is needed for a better understanding of the mechanisms affecting prey abundance by complex predator communities. 2. In a field cage experiment, the effect of increased predator diversity (single species vs. three‐species assemblage) and the presence of weeds (providing structural complexity) on the biological control of cereal aphids were tested and the mechanisms involved were investigated using molecular gut content analysis. 3. The impact of the three‐predator species assemblages of aphid populations was found to be similar to those of the single‐predator species treatments, and the presence or absence of weeds did not alter the patterns observed. This suggests that both predator facilitation and intraguild predation were absent or weak in this system, or that these interactions had counteracting effects on prey suppression. Molecular gut content analysis of predators provided little evidence for the latter hypothesis: predator facilitation was not detected and intraguild predation occurred at a low frequency. 4. The present study suggests additive effects of predators and, therefore, that predator diversity per se neither strengthens nor weakens the biological control of aphids in this system.     

Morphological anti‐predator defences in the nine‐spined stickleback: constitutive,induced or both?

Environmental differences among populations are expected to lead to local adaptation, while spatial or temporal environmental variation within a population will favour evolution of phenotypic plasticity. As plasticity itself can be under selection, locally adapted populations can vary in levels of plasticity. Nine‐spined stickleback (Pungitius pungitius) originating from isolated ponds (low piscine predation risk, high competition) vs. lake and marine populations (high piscine predation risk, low competition) are known to be morphologically adapted to their respective environments. However, nothing is known about their ability to express phenotypic plasticity in morphology in response to perceived predation risk or food availability/competition. We studied predator‐induced phenotypic plasticity in body shape and armour of marine and pond nine‐spined stickleback in a factorial common garden experiment with two predator treatments (present vs. absent) and two feeding regimes (low vs. high). The predation treatment did not induce any morphological shifts in fish from either habitat or food regime. However, strong habitat‐dependent differences between populations as well as strong sexual dimorphism in both body shape and armour were found. The lack of predator‐induced plasticity in development of the defence traits (viz. body armour and body depth) suggests that morphological anti‐predator traits in nine‐spined stickleback are strictly constitutive, rather than inducible. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Invasion success in communities with reciprocal intraguild predation depends on the stage structure of the resident population

The probability of individuals being targeted as prey often decreases as they grow in size. Such size‐dependent predation risk is very common in systems with intraguild predation (IGP), i.e. when predatory species interact through predation and competition. Theory on IGP predicts that community composition depends on productivity. When recently testing this prediction using a terrestrial experimental system consisting of two phytoseiid mite species, Iphiseius degenerans as the IG‐predator and Neoseiulus cucumeris as the IG‐prey, and pollen (Typha latifolia) as the shared resource, we could not find the predicted community shift. Instead, we observed that IG‐prey excluded IG‐predators when the initial IG‐prey/IG‐predator ratio was high, whereas the opposite held when the initial ratio was low, which is also not predicted by theory. We therefore hypothesized that the existence of vulnerable and invulnerable stages in the two populations could be an important driver of the community composition. To test this, we first demonstrate that IG‐prey adults indeed attacked IG‐predator juveniles in the presence of the shared resource. Second, we show that the invasion capacity of IG‐predators at high productivity levels indeed depended on the structure of resident IG‐prey populations. Third, we further confirmed our hypothesis by mimicking successive invasion events of IG‐predators into an established population of IG‐prey at high productivity levels, which consistently failed. Our results show that the interplay between stage structure of populations and reciprocal intraguild predation is decisive at determining the species composition of communities with intraguild predation.     

Salamander evolution across a latitudinal cline in gape-limited predation risk

General predictions of community dynamics require that insights derived from local habitats can be scaled up to explain phenomena across geographic scales. Across these larger spatial extents, adaptation can play an increasing role in determining the outcome of species interactions. If local adaptation is common, then our ability to generalize measures of species interaction strength across communities will be limited without an additional understanding of the genetic variation underlying interaction traits. In the context of predator–prey interactions, prey individuals commonly are expected to reduce risky foraging behaviors and subsequent growth under predation threat. However, rapid growth into a large body size can defend against gape-limited predators, creating a tradeoff between increased predation risk due to elevated foraging activity and decreased predation risk due to large size. Here I combine field observations, natural selection experiments, and common garden assays to understand potential adaptations of spotted salamander Ambystoma maculatum larvae to gape-limited and gape-unconstrained predators. Field observations and natural selection trials suggested antagonistic selection on prey body size among ponds dominated by gape-limited predator salamanders A. opacum and gape-unconstrained beetle larvae Dytiscus . In common garden experiments, prey from sites with high gape-limited predation risk grew larger than those from other sites, suggesting the evolution of rapid growth into a prey size refuge. Larvae from all sites grew to a large size when exposed to the gape-limited N. viridescens predator's kairomones. Hence, induced rapid growth into a size refuge may be an adaptive response to gape-limited predation risk. Results point to an important role for cross-community generalizations based on functional classifications of predators by their gape constraints and inter-site genetic variation in prey growth rates and behaviors.     

Predator biodiversity increases the survivorship of juvenile predators

When predator biodiversity strengthens herbivore suppression, the pattern generally is attributed to interspecific complementarity. However, the relaxation of intraspecific interference within diverse communities has received less attention as an underlying factor, and most experiments to date span much less than one predator generation. Here, working with a community of aphid predators, we compared the survivorship of juvenile predators embedded within diverse versus single-species communities of adult predators. We found that greater predator diversity improved juvenile survivorship for three of four predator taxa (the lady beetles Hippodamia convergens and Coccinella septempunctata, and the bug Nabis alternatus; but not the small bug Geocoris bullatus), whereas survivorship was relatively low when juveniles foraged among only conspecific adults. When aphid densities differed they were lowest for the diverse treatment, and so resource availability could not explain differences in juvenile survivorship. Instead, feeding trials indicated that cannibalism generally posed a greater risk to juveniles than did intraguild predation (with Geocoris again the exception). Our results suggest that the dilution of intraspecific interference may play an important, and perhaps underappreciated, role in shaping predator diversity effects. Furthermore, relatively strong cannibalism but weak intraguild predation has the potential to project diversity effects forward into subsequent generations.     

Dying from the lesser of three evils: facilitation and non‐consumptive effects emerge in a model with multiple predators

Prey modify their behaviour to avoid predation, but dilemmas arise when predators vary in hunting style. Behaviours that successfully evade one predator sometimes facilitate exposure to another predator, forcing the prey to choose the lesser of two evils. In such cases, we need to quantify behavioural strategies in a mix of predators. We model optimal behaviour of Atlantic cod Gadus morhua larvae in a water column, and find the minimal vulnerability from three common predator groups with different hunting modes; 1) ambush predators that sit‐and‐wait for approaching fish larvae; 2) cruising invertebrates that eat larvae in their path; and 3) fish which are visually hunting predators. We use a state‐dependent model to find optimal behaviours (vertical position and swimming speed over a diel light cycle) under any given exposure to the three distinct modes of predation. We then vary abundance of each predator and quantify direct and indirect effects of predation. The nature and strength of direct and indirect effects varied with predator type and abundance. Larvae escaped about half the mortality from fish by swimming deeper to avoid light, but their activity level and cumulative predation from ambush predators increased. When ambush invertebrates dominated, it was optimal to be less active but in more lit habitats, and predation from fish increased. Against cruising predators, there was no remedy. In all cases, the shift in behaviour allowed growth to remain almost the same, while total predation were cut by one third. In early life stages with high and size‐dependent mortality rates, growth rate can be a poor measure of the importance of behavioural strategies.     

Sequential Analysis Reveals Behavioral Differences Underlying Female‐Biased Predation Risk in Stalk‐Eyed Flies

Stalk‐eyed flies are classic models of how sexual selection can drive morphological and behavioral elaboration. Exaggerated ornaments born by stalk‐eyed flies could impose locomotor costs and increase susceptibility to predation; however, a previous study determined that behavior, not eye span, was the major influence on predation risk. Despite the importance of behavior, relatively little is known about how these flies avoid and deter predators. We created an ethogram of behaviors and used it to score individual interactions of male and female Teleopsis dalmanni paired with an actively foraging, generalist arachnid predator (Phidippus audax). Sequential analysis was employed to identify temporal patterns in behavior and determine how males and females differ in their approaches to avoiding predation. Our results indicate that males and females significantly differ when specific behaviors were employed. Patterns in the behavioral transitions suggest that males are more aggressive than females and are more likely to approach a predator to jab, abdomen bob, or display. Males elicited more retreat responses from the predator, whereas females elicited more attacks. Although the behavioral repertoires of male and female stalk‐eyed flies are indistinguishable, their uses of the behaviors differ, particularly the sequential order of presentation, suggesting a strong sex difference in anti‐predatory behavior.