Prey Traits Research Articles

Contemporary evolution and genetic change of prey as a response to predator removal

The ecological effects of predator removal and its consequence on prey behavior have been investigated widely; however, predator removal can also cause contemporary evolution of prey resulting in prey genetic change. Here we tested the role of predator removal on the contemporary evolution of prey traits such as movement, reproduction and foraging. We use EcoSim simulation which allows complex intra- and inter-specific interactions, based on individual evolving behavioral models, as well as complex predator–prey dynamics and coevolution in spatially homogenous and heterogeneous worlds. We model organisms' behavior using fuzzy cognitive maps (FCM) that are coded in their genomes which has a clear semantics making reasoning about causality of any evolved behavior possible. We show that the contemporary evolution of prey behavior owing to predator removal is also accompanied by prey genetic change. We employed machine learning methods, now recognized as holding great promise for the advancement of our understanding and prediction of ecological phenomena. A classification algorithm was used to demonstrate the difference between genomes belonging to prey coevolving with predators and prey evolving in the absence of predation pressure. We argue that predator introductions to naive prey might be destabilizing if prey have evolved and adapted to the absence of predators. Our results suggest that both predator introductions and predator removal from an ecosystem have widespread effects on the survival and evolution of prey by altering their genomes and behavior, even after relatively short time intervals. Our study highlights the need to consider both ecological and evolutionary time scales, as well as the complex interplay of behaviors between trophic levels, in determining the outcomes of predator–prey interactions.

Predator effects on a detritus‐based food web are primarily mediated by non‐trophic interactions

Predator effects on ecosystems can extend far beyond their prey and are often not solely lethally transmitted. Change in prey traits in response to predation risk can have important repercussions on community assembly and key ecosystem processes (i.e. trait-mediated indirect effects). In addition, some predators themselves alter habitat structure or nutrient cycling through ecological engineering effects. Tracking these non-trophic pathways is thus an important, yet challenging task to gain a better grasp of the functional role of predators. Multiple lines of evidence suggest that, in detritus-based food webs, non-trophic interactions may prevail over purely trophic interactions in determining predator effects on plant litter decomposition. This hypothesis was tested in a headwater stream by modulating the density of a flatworm predator (Polycelis felina) in enclosures containing oak (Quercus robur) leaf litter exposed to natural colonization by small invertebrates and microbial decomposers. Causal path modelling was used to infer how predator effects propagated through the food web. Flatworms accelerated litter decomposition through positive effects on microbial decomposers. The biomass of prey and non-prey invertebrates was not negatively affected by flatworms, suggesting that net predator effect on litter decomposition was primarily determined by non-trophic interactions. Flatworms enhanced the deposition and retention of fine sediments on leaf surface, thereby improving leaf colonization by invertebrates - most of which having strong affinities with interstitial habitats. This predator-induced improvement of habitat availability was attributed to the sticky nature of the mucus that flatworms secrete in copious amount while foraging. Results of path analyses further indicated that this bottom-up ecological engineering effect was as powerful as the top-down effect on invertebrate prey. Our findings suggest that predators have the potential to affect substantially carbon flow and nutrient cycling in detritus-based ecosystems and that this impact cannot be fully appreciated without considering non-trophic effects.

Synergistic effects of predators and trematode parasites on larval green frog (Rana clamitans) survival

Parasites and predators can have complex, nonadditive effects on a shared group of victims, which can have important consequences for population dynamics. In particular, parasites can alter host traits that influence predation risk, and predators can have nonconsumptive effects on prey traits which influence susceptibility (i.e., infection intensity and tolerance) to parasites. Here, we examined the combined effects of trematode parasites (Digenea: Echinostomatidae) and odonate (Anax) predators on the survival of larval green frogs (Rana clamitans). First, in a large-scale mesocosm experiment, we manipulated the presence or absence of parasites in combination with the presence of no predator, caged predators, or free predators, and measured survival, traits, and infection. Parasites, caged predators, and free predators decreased survival, and we found a strong negative synergistic effect of parasites in combination with free predators on survival. Importantly, we then examined the potential mechanisms that explain the observed synergistic effect of parasites and predators in a series of follow-up experiments. Results of the follow-up experiments suggest that increased predation susceptibility due to elevated activity levels in the presence of free-swimming parasite infective stages (i.e., an avoidance response) is the most likely mechanism responsible for the observed synergism. These results suggest a potential trade-off in susceptibility to parasites and predators, which can drive nonadditive effects that may have important consequences for natural enemy interactions in natural populations and amphibian conservation.

Nonconsumptive effects in a multiple predator system reduce the foraging efficiency of a keystone predator.

Many studies have demonstrated that the nonconsumptive effect (NCE) of predators on prey traits can alter prey demographics in ways that are just as strong as the consumptive effect (CE) of predators. Less well studied, however, is how the CE and NCE of multiple predator species can interact to influence the combined effect of multiple predators on prey mortality. We examined the extent to which the NCE of one predator altered the CE of another predator on a shared prey and evaluated whether we can better predict the combined impact of multiple predators on prey when accounting for this influence. We conducted a set of experiments with larval dragonflies, adult newts (a known keystone predator), and their tadpole prey. We quantified the CE and NCE of each predator, the extent to which NCEs from one predator alters the CE of the second predator, and the combined effect of both predators on prey mortality. We then compared the combined effect of both predators on prey mortality to four predictive models. Dragonflies caused more tadpoles to hide under leaf litter (a NCE), where newts spend less time foraging, which reduced the foraging success (CE) of newts. Newts altered tadpole behavior but not in a way that altered the foraging success of dragonflies. Our study suggests that we can better predict the combined effect of multiple predators on prey when we incorporate the influence of interactions between the CE and NCE of multiple predators into a predictive model. In our case, the threat of predation to prey by one predator reduced the foraging efficiency of a keystone predator. Consequently, the ability of a predator to fill a keystone role could be compromised by the presence of other predators.

Foraging and vulnerability traits modify predator–prey body mass allometry: freshwater macroinvertebrates as a case study

1. Predation is often size selective, but the role of other traits of the prey and predators in their interactions is little known. This hinders our understanding of the causal links between trophic interactions and the structure of animal communities. Better knowledge of trophic traits underlying predator-prey interactions is also needed to improve models attempting to predict food web structure and dynamics from known species traits. 2. We carried out laboratory experiments with common freshwater macroinvertebrate predators (diving beetles, dragonfly and damselfly larvae and water bugs) and their prey to assess how body size and traits related to foraging (microhabitat use, feeding mode and foraging mode) and to prey vulnerability (microhabitat use, activity and escape behaviour) affect predation strength. 3. The underlying predator-prey body mass allometry characterizing mean prey size and total predation pressure was modified by feeding mode of the predators (suctorial or chewing). Suctorial predators fed upon larger prey and had ˜3 times higher mass-specific predation rate than chewing predators of the same size and may thus have stronger effect on prey abundance. 4. Strength of individual trophic links, measured as mortality of the focal prey caused by the focal predator, was determined jointly by the predator and prey body mass and their foraging and vulnerability traits. In addition to the feeding mode, interactions between prey escape behaviour (slow or fast), prey activity (sedentary or active) and predator foraging mode (searching or ambush) strongly affected prey mortality. Searching predators was ineffective in capturing fast-escape prey in comparison with the remaining predator-prey combinations, while ambush predators caused higher mortality than searching predators and the difference was larger in active prey. 5. Our results imply that the inclusion of the commonly available qualitative data on foraging traits of predators and vulnerability traits of prey could substantially increase biological realism of food web descriptions.

A suite of prey traits determine predator and nutrient enrichment effects in a tri‐trophic food chain

Predation, predation risk, and resource quality affect suites of prey traits that collectively impact individual fitness, population dynamics, and community structure. However, studies of multi‐trophic level effects generally focus on a single prey trait, failing to capture trade‐offs among suites of covarying traits that govern population responses and emergent community patterns. We used structural equation models (SEM) to summarize the non‐lethal and lethal effects of crayfish, Procambarus fallax, and phosphorus (P) addition, which affected prey food quality (periphyton), on the interactive effects of behavioral, morphological, developmental, and reproductive traits of snails, Planorbella duryi. Univariate and multivariate analyses suggested trade‐offs between production (growth, reproduction) and defense (foraging behavior, shell shape) traits of snails in response to non‐lethal crayfish and P addition, but few lethal effects. SEM revealed that non‐lethal crayfish effects indirectly limited per capita offspring standing stock by increasing refuge use, slowing individual growth, and inducing snails to produce thicker, compressed shells. The negative effects of non‐lethal crayfish on snails were strongest with P addition; snails increased allocation to shell defense rather than growth or reproduction. However, compared to ambient conditions, P addition with non‐lethal crayfish still yielded greater per capita offspring standing stock by speeding individual snail growth enabling them to produce more offspring that also grew faster. Increased refuge use in response to non‐lethal crayfish led to a non‐lethal trophic cascade that altered the spatial distribution of periphyton. Independent of crayfish effects, snails stimulated periphyton growth through nutrient regeneration. These findings illustrate the importance of studying suites of traits that reveal costs associated with inducing different traits and how expressing those traits impacts population and community level processes.

Consumer diversity interacts with prey defenses to drive ecosystem function

Prey traits linking consumer diversity to ecosystem function remain poorly understood. On tropical coral reefs, herbivores promote coral dominance by suppressing competing macroalgae, but the roles of herbivore identity and diversity, macroalgal defenses, and their interactions in affecting reef resilience and function are unclear. We studied adjacent pairs of no-take marine reserves and fished areas on reefs in Fiji and found that protected reefs supported 7-17x greater biomass, 2-3x higher species richness of herbivorous fishes, and 3-11x more live coral cover than did fished reefs. In contrast, macroalgae were 27-61x more abundant and 3-4x more species-rich on fished reefs. When we transplanted seven common macroalgae from fished reefs into reserves they were rapidly consumed, suggesting that rates of herbivory (ecosystem functioning) differed inside vs. outside reserves. We then video-recorded feeding activity on the same seven macroalgae when transplanted into reserves, and assessed the functional redundancy vs. complementarity of herbivorous fishes consuming these macroalgae. Of 29 species of larger herbivorous fishes on these reefs, only four species accounted for 97% of macroalgal consumption. Two unicornfish consumed a range of brown macroalgae, a parrotfish consumed multiple red algae, and a rabbitfish consumed a green alga, with almost no diet overlap among these groups. The two most chemically rich, allelopathic algae were each consumed by a single, but different, fish species. This striking complementarity resulted from herbivore species differing in their tolerances to macroalgal chemical and structural defenses. A model of assemblage diet breadth based on our feeding observations predicted that high browser diversity would be required for effective control of macroalgae on Fijian reefs. In support of this model, we observed strong negative relationships between herbivore diversity and macroalgal abundance and diversity across the six study reefs. Our findings indicate that the total diet breadth of the herbivore community and the probability of all macroalgae being removed from reefs by herbivores increases with increasing herbivore diversity, but that a few critical species drive this relationship. Therefore, interactions between algal defenses and herbivore tolerances create an essential role for consumer diversity in the functioning and resilience of coral reefs.

Demographic Consequences of Predators on Prey: Trait and Density Mediated Effects on Mosquito Larvae in Containers

Predators may affect prey population growth and community diversity through density mediated lethal and trait mediated non-lethal effects that influence phenotypic traits of prey. We tested experimentally the roles of thinning the density of prey (lethality) in the absence of predator cues and density and trait mediated effects (lethality + intimidation) of predatory midge Corethrella appendiculata on competing native and invasive mosquito prey. Predator-mediated reductions in prey and density reductions in the absence of C. appendiculata resulted in lower percent survivorship to adulthood and estimates of the finite rate of increase (λ′) for invasive mosquito Aedes albopictus relative to that of controls. In most instances, thinning the density of prey in the absence, but not in the presence, of C. appendiculata cues resulted in lower survivorship to adulthood and λ′ for native mosquito Aedes triseriatus relative to that of controls. Together, these results suggested trait mediated effects of C. appendiculata specific to each species of mosquito prey. Release from intraspecific competition attributable to density reductions in the absence, but not in the presence, of C. appendiculata enhanced growth and lengthened adult lifespan relative to that of controls for A. albopictus but not A. triseriatus. These results show the importance of predator-mediated density and trait mediated effects on phenotypic traits and populations of invasive and native mosquitoes. Species-specific differences in the phenotypic responses of prey may be due, in part, to longer evolutionary history of C. appendiculata with A. triseriatus than A. albopictus.

Costs of predator-induced phenotypic plasticity: a graphical model for predicting the contribution of nonconsumptive and consumptive effects of predators on prey

Defensive modifications in prey traits that reduce predation risk can also have negative effects on prey fitness. Such nonconsumptive effects (NCEs) of predators are common, often quite strong, and can even dominate the net effect of predators. We develop an intuitive graphical model to identify and explore the conditions promoting strong NCEs. The model illustrates two conditions necessary and sufficient for large NCEs: (1) trait change has a large cost, and (2) the benefit of reduced predation outweighs the costs, such as reduced growth rate. A corollary condition is that potential predation in the absence of trait change must be large. In fact, the sum total of the consumptive effects (CEs) and NCEs may be any value bounded by the magnitude of the predation rate in the absence of the trait change. The model further illustrates how, depending on the effect of increased trait change on resulting costs and benefits, any combination of strong and weak NCEs and CEs is possible. The model can also be used to examine how changes in environmental factors (e.g., refuge safety) or variation among predator-prey systems (e.g., different benefits of a prey trait change) affect NCEs. Results indicate that simple rules of thumb may not apply; factors that increase the cost of trait change or that increase the degree to which an animal changes a trait, can actually cause smaller (rather than larger) NCEs. We provide examples of how this graphical model can provide important insights for empirical studies from two natural systems. Implementation of this approach will improve our understanding of how and when NCEs are expected to dominate the total effect of predators. Further, application of the models will likely promote a better linkage between experimental and theoretical studies of NCEs, and foster synthesis across systems.

The relationship between vegetation density and its protective value depends on the densities and traits of prey and predators

Densities of submerged vegetation and those of associated animals tend to co‐vary. This relationship is often attributed to the positive correlation between the density of vegetation and its protective value against predators. However, two counteracting basic elements underlying this paradigm limit its generality. That is, increasing vegetation density should result in decreased predator–prey encounters, whilst at the same time predator–prey encounters should increase as animal densities increase. These two mechanisms should thus counteract each other when the densities of vegetation and associated animals, including both prey and predators, co‐vary. Experimental designs that expose fixed densities of prey and predators to varying densities of vegetation assess only the former mechanism and may thus not properly evaluate the protective value of vegetation in such conditions. By contrast, designs that mimic the naturally co‐varying organism densities test both mechanisms and thus their counteractive impacts on predator–prey encounters. We compared the outcomes of the two alternative designs and carried out additional experiments to explain the putative discrepancy. Increasing vegetation density (mimics of Potamogeton pectinatus) enhanced prey (Daphnia magna) survival only when fixed densities of prey and predators (Perca fluviatilis or Rutilus rutilus) were used. When the animal densities were allowed to co‐vary with vegetation density, vegetation had no impact on prey survival. Instead, prey survival was determined by the aggregate density of prey and predators, shaped by the species‐specific traits of the latter. Thus, the impact of the increased animal densities overrode the impact of the increased vegetation density on predator–prey encounters. It may be insufficient to attribute the co‐variation of vegetation, prey and predator densities simply to the association between vegetation density and its protective value. Increased food resources and reduced competition within vegetation may promote prey and thereby also predator abundance to a greater extent than previously thought.

Diet choice of a predator in the wild: overabundance of prey and missed opportunities along the prey capture sequence

Optimal diet theory (ODT) postulates that predators adjust their foraging decisions by calculating a prey value from the potential biomass gain, handling time, prey vulnerability and encounter rate. Tests of ODT have however so far mainly been restricted to laboratory settings. By video surveillance, we gathered a large data set of more than 2000 field observations of crab spider (Misumena vatia) encounters with potential prey. We then tested whether the complex ODT or two simpler models (prey identity and prey traits) best explain foraging decisions. Insect prey were killed with an average chance of 3.5% when alighting on an inflorescence harboring a spider. Spiders refused to attack suitable prey in 46–79% of encounters when prey was in attack range, indicating an over-abundance of prey relative to the needs of the spiders. Reduction of opportunities to capture prey along the prey capture sequence differed among pollinator groups, with syrphids and solitary bees showing strong avoidance of spiders early in the sequence and bumblebees resisting the final strike. Simple prey traits explained foraging decisions better than ODT, which was not supported. In the absence of food limitation, optimality decisions may be less stringent. The over-abundance of prey indicates that, in contrast to current theory, prey encounter rates are not the most important factor driving predator foraging decisions. Our results are highly coherent with those obtained in earlier field studies on patch leaving strategies and predator-prey encounters. Prey over-abundance and non-optimal predator behavior are apparently not uncommon in nature, and we highlight some of the implications for predator-prey theory.

Seasonal shift in the effect of predators on juvenile Atlantic salmon (Salmo salar) energetics.

Predator effects on prey populations are determined by the number of prey consumed and effects on the traits of surviving prey. Yet, effects of predators on prey traits are rarely evaluated in field studies. We measured the effects of predators on energetic traits (consumption and growth rates) of juvenile Atlantic salmon (Salmo salar) in a large-scale field study. Salmon fry were released at 18 sites that encompassed a wide range in abundance of predatory slimy sculpin (Cottus cognatus). We sampled salmon after 21 and 140 days to measure salmon growth and estimate consumption using a mass-balance model of methylmercury accumulation. Salmon population density was reduced fivefold at sites with abundant sculpin. Over the early season, salmon consumed less where sculpin were abundant, suggesting that reduced foraging under predation risk contributed to predator-caused mortality. In contrast, over the late season, salmon grew more where sculpin were abundant, suggesting that compensatory growth at reduced salmon population density moderated predator-caused mortality. Predator effects on prey energetics can drive variation in survival and growth, with important consequences for population dynamics.

Summer food resource partitioning between four sympatric fish species in Central Spain (River Tormes)

Knowledge of food resource partitioning between sympatric fish species is critical for understanding the fish communities functioning. Four sympatric fish species (Salmo trutta, Pseudochondrostoma duriense, Squalius carolitertii and Barbus bocagei) were captured in August 2010 in the River Tormes (Ávila, Central Spain) in order to study food resource partitioning between fish species such us as a possible mechanism enabling their coexistence, using a fuzzy principal component analysis (FPCA). Diet comparison among species shows that detritus are present in P. duriense, B. bocagei and S. carolitertii, although in different occurrence, showing that these species present typically omnivorous feeding habits. Regarding prevalent food, in all species, benthic prey constituted the most important prey in abundance terms, and terrestrial invertebrates were only consumed by S. trutta, S. carolitertii and P. duriense. High overlap values (Schoener's index from 0.8 up to 1) were found, but it may not indicate competition, since species can adopt different strategies to overcome competence. Thus, prey traits analyses suggest that differences in macrohabitat use, drift behaviour of prey and prey size are important adaptive features that may reduce the inter-specific competition in the fish community and permit the food partitioning that allows coexistence.

Short-term hypoxia modulates Rapana venosa (Muricidae) prey preference in Adriatic lagoons

We studied the effect of short-term hypoxia on predation by the non-native rapa whelk (Rapana venosa) on the three most common bivalve prey in northern Adriatic lagoons: the non-native ark shell (Scapharca inaequivalvis) and Manila clam (Tapes philippinarum), and the native cockle Cerastoderma glaucum. In mesocosm experiments, bivalves were offered to predator as single prey, and as multiple choice of prey. Bivalve prey showed behavioral responses when exposed to short-term hypoxia. Under normoxia, prey were consumed in almost equal numbers when offered separately, but when choice was offered to the predator R. venosa showed a marked preference for S. inaequivalvis. Short-term hypoxia increased the vulnerability of T. philippinarum, and, consequently, rapa whelks modified their predatory behavior and switched their preference to T. philippinarum. We hypothesize this to be a case of environmentally-mediated, non-reciprocal indirect interaction between the two non-native prey species, whose causes are based upon differences in specific traits of prey. Hypoxia may facilitate the coexistence of the two non-native bivalves via predator switching. The native cockle seems the net loser of the game.

Scaling-up anti-predator phenotypic responses of prey: impacts over multiple generations in a complex aquatic community

Non-consumptive effects (NCEs) of predators owing to induced changes in prey traits are predicted to influence the structure of ecological communities. However, evidence of the importance of NCEs is limited primarily to simple systems (e.g. two to four species) over relatively short periods (e.g. less than one generation). We examined the NCEs of a fish predator, arising from phenotypic plasticity in zooplankton prey traits, over multiple generations of a diverse zooplankton community. The presence of fish, caged to remove consumptive effects, strongly influenced zooplankton community structure, through both direct and indirect NCE pathways, altering the abundance of many taxa by magnitudes as large as 3 to 10-fold. Presence of fish affected different species of cladocerans and copepods both positively and negatively. A particularly striking result was the reversal of dominance in copepod taxa: presence of fish reduced the ratio of calanoids to cyclopoids from 6.3 to 0.43. Further, the NCE of fish had a strong negative trophic cascade to zooplankton resources (phytoplankton). To our knowledge, this is the first experiment to show that NCEs can influence the abundance of multiple prey species over time spans of multiple prey generations. Our findings demonstrate that adaptive phenotypic plasticity of individuals can scale-up to affect the structure of ecological communities.

Feeding habits of four sympatric fish species in the Iberian Peninsula: keys to understanding coexistence using prey traits

Trophic interactions are important factors structuring animal communities. We assessed the trophic relations of four fish species that live in sympatry in the River Ladra (NW Spain), and cluster analysis differentiated two feeding strategies: (1) species with omnivorous feeding habits, feeding mainly on detritus and plant material but with aquatic macroinvertebrates as an important complement (Achondrostoma arcasii and Pseudochondrostoma duriense) and (2) species feeding mainly (Salmo trutta) or exclusively (Gasterosteus gymnurus) on aquatic macroinvertebrates. Concerning ingested macroinvertebrates, the trophic overlap was quantified using Schoener’s index and the results obtained revealed a high diet overlap among the species (from 81.3 up to 99.2%). In order to get a deeper insight into mechanisms of fish species coexistence, we used ten biological and ecological traits of macroinvertebrate prey to discriminate feeding preferences. As a result, despite the high similarity among the diets, our analyses suggest that differences in diel activity patterns and drift behaviour of preys, as well as differences in the prey size, are important adaptive features that may reduce the inter-specific competition in the fish community and permit the partitioning of food that allows coexistence.

Multiple prey cues induce foraging flexibility in a trap-building predator

Predators must be behaviourally flexible to counter the temporal and spatial stochastic fluctuations and response variability of their prey. To ensure behaviours are adequate across environments, animals must regularly assess environmental cues. Spider orb webs are an example of a flexible foraging trait in a predator, as web architectural components vary in response to exposure to different prey types and prey traits. The cues used by orb web spiders to initiate changes in web architecture are not known. Current research predicts that prey nutrients and vibratory stimuli are potential candidates, but how they combine to affect spider foraging decisions is not clear. We performed experiments exposing the giant wood spider, Nephila pilipes, to different prey nutrients and vibratory stimuli. Spiders were fed either large profitable prey with high kinetic energy (crickets) or small prey with low kinetic energy (flies). In two treatments the prey nutrients and vibratory cues came from live prey, but in the other two treatments spiders received dead crickets with webs stimulated by flies and vice versa. The spiders fed on live flies built larger webs with more radii that were less stiff and had greater vibration damping. These web characteristics did not differ between the other three treatment groups. Our results show that in the absence of nutrient and vibratory cues from profitable prey, spiders alter their web architecture to build webs better able to capture the less profitable prey at a cost of more material investment, greater web visibility and reduced vibratory signal clarity.

Costs and benefits of defences induced by predators differing in dangerousness

While theoretical studies predict that inducible defences should be fine-tuned according to the qualities of the predator, very few studies have investigated how dangerousness of predators, i.e. the rate at which predators kill prey individuals, affects the strength of phenotypic responses and resulting benefits and costs of induced defences. We performed a comprehensive study on fitness consequences of predator-induced responses by involving four predators (leech, water scorpion, dragonfly larva and newt), evaluating costs and benefits of responses, testing differences in dangerousness between predators and measuring responses in several life history traits of prey. We raised Rana dalmatina tadpoles in the presence of free-ranging predators, in the presence of caged predators, and exposed naive and experienced tadpoles to free-ranging predators. Tadpoles adjusted the intensities of their behavioural and morphological defences to predator dangerousness. Survival was lower in the nonlethal presence of the most dangerous predator, while we could not detect costs of induced defences at or after metamorphosis. When exposed to free-ranging predators, small, but not large, tadpoles benefited from exhibiting an induced phenotype in terms of elevated survival when compared to naive tadpoles, but we did not observe higher survival either in tadpoles exhibiting more extreme phenotypes or in tadpoles exposed to the type of predator they were raised with. These results indicate that while predator-induced defences can mirror dangerousness of predators, costs and benefits do not necessarily scale to the magnitude of plastic responses.

Are you experienced? Predator type and predator experience trade‐offs in relation to tadpole mortality rates

Cryptic behavior and unpalatability are common defensive strategies that occur in different taxonomic groups, but the effectiveness of these defensive strategies is context dependent, varying with predator type and co-occurring species. We tested this assumption by measuring the mortality rates of Eupemphix nattereri (cryptic behavior) and Rhinella schneideri (unpalatable) tadpoles in association with the predatory fish Oreochromis niloticus (vertebrate) and the dragonfly larvae of Aeshna sp. (invertebrate). We designed a second experiment to evaluate whether fish predators are capable of learning to avoid unpalatable prey once they have encountered it. Our results showed that fish preyed selectively on palatable tadpoles, avoiding unpalatable tadpoles and that the odonate larvae were more efficient in preying on the more active unpalatable tadpoles and less efficient in capturing those tadpoles that presented cryptic behaviors. Additionally, our data suggest that the antipredator traits of tadpoles can interact with each other, with cryptic tadpoles showing lesser mortality when co-occurring with unpalatable tadpoles and odonate predators. Unpalatable tadpoles also increase the mortality of cryptic tadpoles in the presence of experienced fish predators. These prey traits interact in modifying the prey preference of the predator, which constitutes a prey-induced trait-mediated interaction (TMI). This type of TMI is dependent on the system complexity (number of predator and prey species interactions) and could define food web properties, such as the role of predators and the number of competitor species in the system.

Spatial distribution of lion kills determined by the water dependency of prey species

Predation risk from lions (Panthera leo) has been linked to habitat characteristics and availability and traits of prey. We separated the effects of vegetation density and the presence of drinking water by analyzing locations of lion kills in relation to rivers with dense vegetation, which offer good lion stalking opportunities, and artificial water points with low vegetation density. The spatial distribution of lion kills was studied at the Klaserie Private Nature Reserve, South Africa. The distance between 215 lion kills and the nearest water source was analyzed using generalized linear models. Lions selected medium-sized prey species. Lion kills were closer to rivers and to artificial water points than expected by random distribution of the kills. Water that attracted prey, and not the vegetation density in riverine areas, increased predation risk, with kills of buffalo (Syncerus caffer), kudu (Tragelaphus strepsiceros), and wildebeest (Connochaetes taurinus) as water-dependent prey species. Traits of prey species, including feeding type (food habits), digestion type (ruminant or nonruminant); or body size, did not explain locations of lion kills, and no seasonal patterns in lion kills were apparent. We argue that the cascading impact of lions on local mammal assemblages is spatially heterogeneous.