Predator (<Emphasis Type="Italic">Carcinus maenas</Emphasis>) nonconsumptive limitation of prey (<Emphasis Type="Italic">Nucella lapillus</Emphasis>) feeding depends on prey density and predator cue type

Predators often have nonconsumptive effects (NCEs) on prey. For example, upon detection of predator cues, prey can reduce feeding activities to hamper being detected by predators. Previous research showed that waterborne chemical cues from green crabs (Carcinus maenas, predator) limit the dogwhelk (Nucella lapillus, prey) consumption of barnacles regardless of dogwhelk density, even though individual predation risk for dogwhelks decreases with conspecific density. Such NCEs might disappear with dogwhelk density if dogwhelks feed on mussels, as mussel stands constitute better antipredator refuges than barnacle stands. Through a laboratory experiment, we effectively found that crab chemical cues limit the per-capita consumption of mussels by dogwhelks at low dogwhelk density but not at high density. The combination of tactile and chemical cues from crabs, however, limited the dogwhelk consumption of mussels at both dogwhelk densities. The occurrence of such NCEs at both dogwhelk densities could have resulted from tactile cues indicating a stronger predation risk than chemical cues alone. Overall, the present study reinforces the notions that prey evaluate conspecific density when assessing predation risk and that predator cue type affects their perception of risk.     

Tadpoles of the bronze frog (Rana temporalis) assess predation risk before evoking antipredator defense behavior

Predation threat-associated behavioral response was studied in Rana temporalis tadpoles to discover the importance of predators’ visual and chemical cues (kairomones and diet-derived metabolites of consumed prey) in evoking antipredator behavior. The caged predators (dragonfly larvae) fed on prey tadpoles or insects (Notonecta spp.) and water conditioned with the predators provided the threat stimuli to the tadpole prey. The predators’ visual cues were ineffective in evoking antipredator behaviors in the tadpole prey. However, exposure to caged tadpole-fed predators or water conditioned with tadpole-fed predators elicited predator avoidance behavior in the tadpoles; they stayed away from the predators, significantly reduced swimming activity (swimming time and distance traveled), and increased burst speed. Interestingly, exposure to water conditioned with starved predators did not elicit any antipredator behavior in the prey. Further, the antipredator responses of predator-experienced tadpoles were significantly greater than those exhibited by predator-na?ve tadpoles. The study shows that R. temporalis tadpoles assess predation threat based exclusively on chemical cues emanating from the predators’ dietary metabolites and that the inclusion of conspecific prey items in the diet of the predators is perceived as a threat. The study also shows that antipredator behavior in these tadpoles is innate and is enhanced during subsequent encounters with the predators.     

Predator density and the functional responses of coral reef fish

Predation is a key process driving coral reef fish population dynamics, with higher per capita prey mortality rates on reefs with more predators. Reef predators often forage together, and at high densities, they may either cooperate or antagonize one another, thereby causing prey mortality rates to be substantially higher or lower than one would expect if predators did not interact. However, we have a limited mechanistic understanding of how prey mortality rates change with predator densities. We re-analyzed a previously published observational dataset to investigate how the foraging response of the coney grouper (Cephalopholis fulva) feeding on the bluehead wrasse (Thalassoma bifasciatum) changed with shifts in predator and prey densities. Using a model-selection approach, we found that per-predator feeding rates were most consistent with a functional response that declines as predator density increases, suggesting either antagonistic interactions among predators or a shared antipredator behavioral response by the prey. Our findings suggest that variation in predator density (natural or anthropogenic) may have substantial consequences for coral reef fish population dynamics.     

Do anuran larvae respond behaviourally to chemical cues from an invasive crayfish predator? A community-wide study

Antipredator behaviour is an important fitness component in most animals. A co-evolutionary history between predator and prey is important for prey to respond adaptively to predation threats. When non-native predator species invade new areas, native prey may not recognise them or may lack effective antipredator defences. However, responses to novel predators can be facilitated by chemical cues from the predators’ diet. The red swamp crayfish Procambarus clarkii is a widespread invasive predator in the Southwest of the Iberian Peninsula, where it preys upon native anuran tadpoles. In a laboratory experiment we studied behavioural antipredator defences (alterations in activity level and spatial avoidance of predator) of nine anurans in response to P. clarkii chemical cues, and compared them with the defences towards a native predator, the larval dragonfly Aeshna sp. To investigate how chemical cues from consumed conspecifics shape the responses, we raised tadpoles with either a tadpole-fed or starved crayfish, or dragonfly larva, or in the absence of a predator. Five species significantly altered their behaviour in the presence of crayfish, and this was largely mediated by chemical cues from consumed conspecifics. In the presence of dragonflies, most species exhibited behavioural defences and often these did not require the presence of cues from predation events. Responding to cues from consumed conspecifics seems to be a critical factor in facilitating certain behavioural responses to novel exotic predators. This finding can be useful for predicting antipredator responses to invasive predators and help directing conservation efforts to the species at highest risk.     

Predator–prey naïveté, antipredator behavior,and the ecology of predator invasions

We present a framework for explaining variation in predator invasion success and predator impacts on native prey that integrates information about predator–prey naïveté, predator and prey behavioral responses to each other, consumptive and non‐consumptive effects of predators on prey, and interacting effects of multiple species interactions. We begin with the ‘naïve prey’ hypothesis that posits that naïve, native prey that lack evolutionary history with non‐native predators suffer heavy predation because they exhibit ineffective antipredator responses to novel predators. Not all naïve prey, however, show ineffective antipredator responses to novel predators. To explain variation in prey response to novel predators, we focus on the interaction between prey use of general versus specific cues and responses, and the functional similarity of non‐native and native predators. Effective antipredator responses reduce predation rates (reduce consumptive effects of predators, CEs), but often also carry costs that result in non‐consumptive effects (NCEs) of predators. We contrast expected CEs versus NCEs for non‐native versus native predators, and discuss how differences in the relative magnitudes of CEs and NCEs might influence invasion dynamics. Going beyond the effects of naïve prey, we discuss how the ‘naïve prey’, ‘enemy release’ and ‘evolution of increased competitive ability’ (EICA) hypotheses are inter‐related, and how the importance of all three might be mediated by prey and predator naïveté. These ideas hinge on the notion that non‐native predators enjoy a ‘novelty advantage’ associated with the naïveté of native prey and top predators. However, non‐native predators could instead suffer from a novelty disadvantage because they are also naïve to their new prey and potential predators. We hypothesize that patterns of community similarity and evolution might explain the variation in novelty advantage that can underlie variation in invasion outcomes. Finally, we discuss management implications of our framework, including suggestions for managing invasive predators, predator reintroductions and biological control.     

Cue reliability, risk sensitivity and inducible morphological defense in a marine snail

Reliable cues that communicate current or future environmental conditions are a requirement for the evolution of adaptive phenotypic plasticity, yet we often do not know which cues are responsible for the induction of particular plastic phenotypes. I examined the single and combined effects of cues from damaged prey and predator cues on the induction of plastic shell defenses and somatic growth in the marine snail Nucella lamellosa. Snails were exposed to chemical risk cues from a factorial combination of damaged prey presented in isolation or consumed by predatory crabs (Cancer productus). Water-borne cues from damaged conspecific and heterospecific snails did not affect plastic shell defenses (shell mass, shell thickness and apertural teeth) or somatic growth in N. lamellosa. Cues released by feeding crabs, independent of prey cue, had significant effects on shell mass and somatic growth, but only crabs consuming conspecific snails induced the full suite of plastic shell defenses in N. lamellosa and induced the greatest response in all shell traits and somatic growth. Thus the relationship between risk cue and inducible morphological defense is dependent on which cues and which morphological traits are examined. Results indicate that cues from damaged conspecifics alone do not trigger a response, but, in combination with predator cues, act to signal predation risk and trigger inducible defenses in this species. This ability to “label” predators as dangerous may decrease predator avoidance costs and highlights the importance of the feeding habits of predators on the expression of inducible defenses.     

Predators as drivers of insect defenses

Insects have evolved various types of antipredator defenses. For example, many insects have evolved crypsis, and exhibit cryptic body colors and shapes for hiding from predators. Other insects produce toxins as a form of chemical defense against predators, and some toxic insects are aposematic, with conspicuous body colors for advertising their toxins. Insects can also develop hairs, spines or hard exoskeletons as morphological defenses to protect themselves from predation. In addition, insects can evolve behavioral defenses, in which insects exhibit autotomy or dropping, or feign death. This study investigated which predator types evoke these types of defenses, through a review of the effectiveness of antipredator defenses in insects against carnivorous animals that are commonly used as model predators in studies. These predators include other insects, spiders, fish, frogs, lizards, birds and mammals. The results provide the first step for clarifying the evolutionary drivers of antipredator defenses in insects. The following aspects should be considered for future studies: multiple predator species and sufficient replication, alternative prey and predator models, and tolerance to predators in insects.     

Inducible defenses in Olympia oysters in response to an invasive predator

The prey naiveté hypothesis suggests that native prey may be vulnerable to introduced predators because they have not evolved appropriate defenses. However, recent evidence suggests that native prey sometimes exhibit induced defenses to introduced predators, as a result of rapid evolution or other processes. We examined whether Olympia oysters (Ostrea lurida) display inducible defenses in the presence of an invasive predator, the Atlantic oyster drill (Urosalpinx cinerea), and whether these responses vary among oyster populations from estuaries with and without this predator. We spawned oysters from six populations distributed among three estuaries in northern California, USA, and raised their offspring through two generations under common conditions to minimize effects of environmental history. We exposed second-generation oysters to cue treatments: drills eating oysters, drills eating barnacles, or control seawater. Oysters from all populations grew smaller shells when exposed to drill cues, and grew thicker and harder shells when those drills were eating oysters. Oysters exposed to drills eating other oysters were subsequently preyed upon at a slower rate. Although all oyster populations exhibited inducible defenses, oysters from the estuary with the greatest exposure to drills grew the smallest shells suggesting that oyster populations have evolved adaptive differences in the strength of their responses to predators. Our findings add to a growing body of literature that suggests that marine prey may be less likely to exhibit naiveté in the face of invasive predators than prey in communities that are more isolated from native predators, such as many freshwater and terrestrial island ecosystems.     

Linking Morphological and Behavioural Defences: Prey Fish Detect the Morphology of Conspecifics in the Odour Signature of their Predators

Predation is a strong selective force acting on both morphology and behaviour of prey animals. While morphological defences (e.g. crypsis, presence of armours or spines or specific body morphologies) and antipredator behaviours (e.g. change in foraging or reproductive effort, or hiding and fleeing behaviours) have been widely studied separately, few studies have considered the interplay between the two. The question raised in our study is whether antipredator behaviours of a prey fish to predator odours could be influenced by the morphology of prey conspecifics in the diet of the predator. We used goldfish (Carassius auratus) as our test species; goldfish exposed to predation risk significantly increase their body depth to length ratio, which gives them a survival advantage against gape‐limited predators. We exposed shallow‐bodied and deep‐bodied goldfish to the odour of pike (Esox lucius) fed either form of goldfish. Deep‐bodied goldfish displayed lower intensity antipredator responses than shallow‐bodied ones, consistent with the hypothesis that individuals with morphological defences should exhibit less behavioural modification than those lacking such defences. Moreover, both shallow‐ and deep‐bodied goldfish displayed their strongest antipredator responses when exposed to the odour of pike fed conspecifics of their own morphology, indicating that goldfish are able to differentiate the morphology of conspecifics through predator diet cues. For a given individual, predator threat increases as the prey become more like the individual eaten, revealing a surprising level of sophistication of chemosensory assessment by prey fish.     

Morphological and life‐history responses of anurans to predation by an invasive crayfish: an integrative approach

Predator‐induced phenotypic plasticity has been widely documented in response to native predators, but studies examining the extent to which prey can respond to exotic invasive predators are scarce. As native prey often do not share a long evolutionary history with invasive predators, they may lack defenses against them. This can lead to population declines and even extinctions, making exotic predators a serious threat to biodiversity. Here, in a community‐wide study, we examined the morphological and life‐history responses of anuran larvae reared with the invasive red swamp crayfish, Procambarus clarkii, feeding on conspecific tadpoles. We reared tadpoles of nine species until metamorphosis and examined responses in terms of larval morphology, growth, and development, as well as their degree of phenotypic integration. These responses were compared with the ones developed in the presence of a native predator, the larval dragonfly Aeshna sp., also feeding on tadpoles. Eight of the nine species altered their morphology or life history when reared with the fed dragonfly, but only four when reared with the fed crayfish, suggesting among‐species variation in the ability to respond to a novel predator. While morphological defenses were generally similar across species (deeper tails) and almost exclusively elicited in the presence of the fed dragonfly, life‐history responses were very variable and commonly elicited in the presence of the invasive crayfish. Phenotypes induced in the presence of dragonfly were more integrated than in crayfish presence. The lack of response to the presence of the fed crayfish in five of the study species suggests higher risk of local extinction and ultimately reduced diversity of the invaded amphibian communities. Understanding how native prey species vary in their responses to invasive predators is important in predicting the impacts caused by newly established predator–prey interactions following biological invasions.     

The advantage of no defense: predation enhances cohort survival in a desert amphibian

The impacts that predators have on prey behavior, growth, survival, and ultimately the composition of many ecological communities are mediated by prey defenses and the susceptibility of prey to predators. We hypothesized that prey populations inhabiting short-lived, species-poor, aquatic environments should lack significant morphological, developmental, and behavioral responses to predators and are therefore highly susceptible to predation. Furthermore, we predicted that the resultant decrease in prey density and increase in per capita resources due to high susceptibility to predators should enhance overall cohort survival because of enhanced growth of surviving prey. To test these ideas, we performed laboratory and outdoor mesocosm experiments to disentangle multiple effects of predators on an anuran (Scaphiopus couchii); a species highly adapted to breeding in ephemeral habitats and that has one of the shortest larval periods of all anurans. Chemical (presence of predator) and lethal predator cues (predator plus consumed conspecific) elicited no response in behavior, development, or morphology, indicating a lack of defensive mechanisms. Survivorship was significantly reduced in treatments where tadpoles were exposed to predators. However, this reduction in prey density led to accelerated time to metamorphosis, conferring an advantage to survivors who must metamorphose before ephemeral ponds dry. Our experiments demonstrated that in short-lived environments, prey may exhibit little or no response to the presence of predators presumably because selection for anti-predator defenses is countered by selection for rapid metamorphosis. However, predation actually resulted in an increase in overall cohort survival. Although predators are relatively rare in highly ephemeral aquatic environments, they may play an important role in facilitating the long-term persistence of their prey by reducing prey density.     

Type and nature of cues used by Nucella lapillus to evaluate predation risk

The ability of prey to detect and adequately respond to predation risk influences immediate survival and overall fitness. Chemical cues are commonly used by prey to evaluate risk, and the purpose of this study was to elicit the nature of cues used by prey hunted by generalist predators. Nucella lapillus are common, predatory, intertidal snails that evaluate predatory risk using chemical cues. Using Nucella and a suite of its potential predators as a model system, we explored how (1) predator type, (2) predator diet, and (3) injured conspecifics and heterospecifics influence Nucella behavior. Using laboratory flumes, we determined that Nucella responded only to the invasive green crab (Carcinus maenas), the predator it most frequently encounters. Nucella did not respond to rock crabs (Cancer irroratus) or Jonah crabs (Cancer borealis), which are sympatric predators but do not frequently encounter Nucella because these crabs are primarily subtidal. Predator diet did not affect Nucella responses to risk, although starved predator response was not significantly different from controls. Since green crabs are generalist predators, diet cues do not reflect predation risk, and thus altering behavior as a function of predator diet would not likely benefit Nucella. Nucella did, however, react to injured conspecifics, a strategy that may allow them to recognize threats when predators are difficult to detect. Nucella did not react to injured heterospecifics including mussels (Mytilus edulis) and herbivorous snails Littorina littorea, suggesting that they are responding to chemical cues unique to their species. The nature of cues used by Nucella allows them to minimize costs associated with predator avoidance.     

Hydrodynamic mediation of predator-prey interactions: differential patterns of prey susceptibility and predator success explained by variation in water flow

In most shallow water marine systems, fluid movements vary on scales that may influence local community dynamics both directly, through changes in the abundance of species, and indirectly, by modifying important behaviors of organisms. We examined how differences in current speed affect the outcome of predator-prey interactions for two species of marine benthic predators (knobbed whelks, Busycon carica, and blue crabs, Callinectes sapidus) foraging on two common prey species (bay scallops, Argopecten irradians, and hard clams, Mercenaria mercenaria). The predators differ in their foraging strategies and prey in their potential escape responses. Predation by blue crabs, highly mobile predators/scavengers that rely upon chemical odors transported in the water column to locate prey, could be strongly affected by changes in current speed and turbulent mixing because their foraging strategy relies on a high degree of spatial integration of prey odor plumes. Whelks, slow moving, predatory gastropods that often forage with their bodies buried in the sediment, may be less susceptible to flow-induced distortion of prey odor plumes because their sluggish movements result in a high degree of temporal integration of prey odors. Bay scallops, relatively mobile bivalves capable of rapid short-distance swimming burst, and hard clams, sedentary bivalves, have been shown to respond to varying degrees to predator odors that are dispersed in the water column. Flow regime for the predator-prey experiments was manipulated in situ using large channels. Predation by blue crabs on both juvenile hard clams and bay scallops decreased with increases in water flow (0-12 vs. 0-30 cm s⁻¹). Whelk predation on bay scallops increased with increases in water flow, whereas predation by whelks on hard clams did not differ between flow regimes. For blue crabs movement decreased at periods of high water flow. Because blue crabs locate prey through chemolocation of water-borne cues, which are diluted rapidly at higher flows, decreases in foraging may result from the inability to successfully detect prey at enhanced flows. Differences in predation by whelks could not be explained by a similar mechanism. Visual observations of foraging whelks revealed no differences in whelk behavior between the two flow regimes. The pattern of higher whelk predation on scallops at enhanced flow is likely to be related to a flow-inhibiting ability of scallops to detect predator approach. Thus, flow enhancement interferes with three of the predator-prey systems but the effect on predator success depends on whether the predator or prey is most affected.     

Recognition and Response to Native and Novel Predators in the Largespring mosquitofish,Gambusia geiseri

The introduction of predator species into new habitats is an increasingly common consequence of human activities, and the persistence of native prey species depends upon their response to these novel predators. In this study, we examined whether the Largespring mosquitofish, Gambusia geiseri exhibited antipredator behavior and/or an elevation of circulating stress hormones (cortisol) to visual and chemical cues from a native predator, a novel predator, or a non‐predatory control fish. Prey showed the most pronounced antipredator response to the native predator treatment, by moving away from the stimulus, while the prey showed no significant changes in their vertical or horizontal position in response to the novel or non‐predator treatments. We also found no significant difference in water‐borne cortisol release rates following any of the treatments. Our results suggest the prey did not recognize and exhibit antipredator behavior to the novel predator, and we infer that this predator species could be detrimental if it expands into the range of this prey species. Further, our study demonstrates prey may not respond to an invasive predator that is phylogenetically, behaviorally, and morphologically dissimilar from the prey species' native predators.     

Predator–prey interactions and metabolic rates are altered in stable and unstable groups in a social fish

Understanding the determinants and consequences of predation effort, success and prey responses is important since these factors affect the fitness of predators and prey. When predators are also invasive species, the impacts on prey can be particularly far-reaching with ultimate ecosystem-level consequences. However, predators are typically viewed as behaviourally fixed within this interaction and it is unclear how variation in predator social dynamics affects predator–prey interactions. Using the invasive eastern mosquitofish Gambusia holbrooki and a native glass shrimp Paratya australiensis in Australia, we investigated how varying levels of social conflict within predator groups influences predator–prey interactions. By experimentally manipulating group stability of G. holbrooki, we show that rates of social conflict were lower in groups with large size differences, but that routine metabolic rates were higher in groups with large size differences. Predation effort and success did not vary depending on group stability, but in stable groups predation effort by aggressive dominants was greater than subordinates. The anti-predator responses of prey to the stability of predator groups were mixed. While more prey utilized shelters when exposed to stable compared to unstable groups of predators, a greater proportion were sedentary when predator groups were unstable. Overall, this study demonstrates predator group stability is modulated by differences in body size and can influence prey responses. Further, it reveals a hidden metabolic cost of living in stable groups despite reduced overt social conflict. For invasive species management, it is therefore important to consider the behavioural and physiological plasticity of the invasive predators, whose complex social interactions and metabolic demands can modulate patterns of predator–prey interactions.     

The Effects of Relaxed and Reversed Selection by Predators on the Antipredator Behavior of the Threespine Stickleback, Gasterosteus aculeatus

Isolation from predators can lead to the reduction or loss of ancestral behavioral defenses in prey, but does not always do so. Predators introduced to populations that have experienced relaxed selection from some ancestral predators can favor the evolution of antipredator behavior that has been lost. We examined these possibilities by eliciting antipredator behavior in three populations of threespine stickleback fish, Gasterosteus aculeatus : an oceanic population thought to resemble the ancestral form, and two populations historically (up to 20 000 yr) devoid of piscine predators (relaxed selection), one of which has been stocked with salmonids for nearly 25 yr (reversed selection). We used three kinds of predator models: a sculpin (ambush predator), a rainbow trout (chasing predator), and an overhead silhouette of an arctic tern. Stickleback reacted differently to the three models, indicating that they distinguished among them. Individuals from all populations responded similarly to the tern model. The ancestral population showed the weakest response to the sculpin model despite being the only population that encounters these predators naturally. Stickleback from the trout-free population displayed slightly reduced responses to the trout model, and recovery times like those in the ancestral population providing only weak evidence for loss of the ancestral antipredator repertoire. Fish from the reverse-selected population exhibited fascinating, elevated responses to both the trout and sculpin models relative to the other two populations. These findings offer initial evidence of (1) a partial alteration of the ancestral behavioral repertoire during a long period of relaxed selection from piscine predators, and (2) rapid acquisition of extreme responses to piscine predators under reverse selection.     

Referential calls signal predator behavior in a group-living bird species

Predation is a powerful agent of natural selection, driving the evolution of antipredator calls [1]. These calls have been shown to communicate predator category [2-4] and/or predator distance to conspecifics [5-7]. However, the risk posed by predators depends also on predator behavior [8], and the ability of prey to communicate predator behavior to conspecifics would be a selective advantage reducing their predation risk. I tested this idea in Siberian jays (Perisoreus infaustus), a group-living bird species. Predation by hawks, and to a lesser extent by owls, is substantial and the sole cause of mortality in adult jays [9]. By using field data and predator-exposure experiments, I show here that jays used antipredator calls for hawks depending on predator behavior. A playback experiment demonstrated that these prey-to-prey calls were specific to hawk behavior (perch, prey search, attack) and elicited distinct, situation-specific escape responses. This is the first study to demonstrate that prey signals convey information about predator behavior to conspecifics. Given that antipredator calls in jays aim at protecting kin group members [10, 11], consequently lowering their mortality [9], kin-selected benefits could be an important factor for the evolution of predator-behavior-specific antipredator calls in such systems.     

Partitioning mechanisms of Predator Interference in different Habitats

Prey are often consumed by multiple predator species. Predation rates on shared prey species measured in isolation often do not combine additively due to interference or facilitation among the predator species. Furthermore, the strength of predator interactions and resulting prey mortality may change with habitat type. We experimentally examined predation on amphipods in rock and algal habitats by two species of intertidal crabs, Hemigrapsus sanguineus (top predators) and Carcinus maenas (intermediate predators). Algae provided a safer habitat for amphipods when they were exposed to only a single predator species. When both predator species were present, mortality of amphipods was less than additive in both habitats. However, amphipod mortality was reduced more in rock than algal habitat because intermediate predators were less protected in rock habitat and were increasingly targeted by omnivorous top predators. We found that prey mortality in general was reduced by (1) altered foraging behavior of intermediate predators in the presence of top predators, (2) top predators switching to foraging on intermediate predators rather than shared prey, and (3) density reduction of intermediate predators. The relative importance of these three mechanisms was the same in both habitats; however, the magnitude of each was greater in rock habitat. Our study demonstrates that the strength of specific mechanisms of interference between top and intermediate predators can be quantified but cautions that these results may be habitat specific. An erratum to this article can be found at     

When is general wariness favored in avoiding multiple predator types?

Adaptive responses to predation are generally studied assuming only one predator type exists, but most prey species are depredated by multiple types. When multiple types occur, the optimal antipredator response level may be determined solely by the probability of attack by the relevant predator: "specific responsiveness." Conversely, an increase in the probability of attack by one predator type might increase responsiveness to an alternative predator type: "general wariness." We formulate a mathematical model in which a prey animal perceives a cue providing information on the probability of two predator types being present. It can perform one of two evasive behaviors that vary in their suitability as a response to the "wrong" predator type. We show that general wariness is optimal when incorrect behavioral decisions have differential fitness costs. Counterintuitively, difficulty in discriminating between predator types does not favor general wariness. We predict that where responses to predator types are mutually exclusive (e.g., referential alarm-calling), specific responsiveness will occur; we suggest that prey generalize their defensive responses based on cue similarity due to an assumption of response utility; and we predict, with relevance to conservation, that habituation to human disturbance should generalize only to predators that elicit the same antipredator response as humans.