Population divergence in growth rate and antipredator defences in Rana arvalis

Growth and development rates often differ among populations of the same species, yet the factors maintaining this differentiation are not well understood. We investigated the antipredator defences and their efficiency in two moor frog Rana arvalis populations differing in growth and development rates by raising tadpoles in outdoor containers in the nonlethal presence and absence of three different predators (newt, fish, dragonfly larva), and by estimating tadpole survival in the presence of free-ranging predators in a laboratory experiment. Young tadpoles in both populations reduced activity in the presence of predators and increased hiding behaviour in the presence of newt and fish. Older tadpoles from the slow-growing Gotland population (G) had stronger hiding behaviour and lower activity in all treatments than tadpoles from the fast-growing Uppland population (U). However, both populations showed a plastic behavioural response in terms of reduced activity. The populations differed in induced morphological defences especially in response to fish. G tadpoles responded with relatively long and deep body, short tail and shallow tail muscle, whereas the responses in U tadpoles were often the opposite and closer to the responses induced by the other predators. U tadpoles metamorphosed earlier, but at a similar size to G tadpoles. There was no evidence that growth rate was affected by predator treatments, but tadpoles metamorphosed later and at larger size in the predator treatments. G tadpoles survived better in the presence of free-ranging predators than U tadpoles. These results suggest that in these two populations, low growth rate was linked with low activity and increased hiding, whereas high growth rate was linked with high activity and less hiding. The differences in behaviour may explain the difference in survival between the populations, but other mechanisms (i.e. differences in swimming speed) may also be involved. There appears to be considerable differentiation in antipredator responses between these two R. arvalis populations, as well as with respect to different predators.     

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.     

Functional mechanisms of an inducible defence in tadpoles: morphology and behaviour influence mortality risk from predation

In many amphibian larvae a suite of morphological and behavioural characters varies together in an induced defence against predators, but it remains unclear which features are functionally related to defence. We independently manipulated behaviour and morphology in tadpoles of Hyla versicolor and assessed their consequences for swimming performance and predator escape. Data on burst swimming showed that tadpoles which accelerated rapidly were elongate, with shallow bodies and tails. Predator escape was measured by exposing tadpoles to predators (larval Anax dragonflies or larval Ambystoma salamanders) and recording time until death. Tadpoles were first reared for 30 days in ponds containing either caged Anax or no predators; individuals responded to predators by developing large brightly coloured tails and short bodies. We placed tadpoles of both morphological phenotypes into plastic tubs, and manipulated their behaviour using food and chemical cues from predators. Mortality risk experienced by the predator‐induced phenotype was about half that of the no‐predator phenotype, and risk increased with time spent swimming. An interaction between morphology and behaviour arose because increasing activity caused higher risk for tadpoles with deep tail fins but not shallow tail fins.     

Effects of Sibship and the Presence of Multiple Predators on the Behavior of Green Frog (Rana clamitans) Tadpoles

In nature, prey are exposed to multiple predators simultaneously. We examined the effects of the cues of two potential predators, mosquitofish and odonate larvae, individually and in combination on the behavior of green frog (Rana clamitans) tadpoles. In addition to examining the behavioral response of green frog tadpoles to multiple predators, we examined variation in behavior among tadpoles from different egg masses (i.e. different sibships). Sibships differed in activity level and there was a significant predator cue by sibship interaction. Two sibships were relatively more active in the control and odonate predator cue treatments but showed reduced activity in treatments containing mosquitofish cues, whereas the remaining sibships showed consistently low levels of activity in all predator cue treatments, including the control. The use of the vegetated side of the aquarium did not differ between tadpoles exposed to the different predator cues. Sibship had no effect on tadpoles’ use of the vegetated side of the aquarium, and there was no interaction between sibship and predator cue. Our results suggest that green frogs did not respond to simultaneous exposure to multiple predator cues any differently than they did to exposure to individual predator cues. More importantly, our results suggest variation, possibly genetically based, in behavioral responses of tadpoles to predators, and thus selection on these behaviors is possible. Of particular interest is that there was variation in behavioral responses to a non‐native predator (Gambusia affinis), suggesting an evolutionary response to an invasive predator is possible.     

Risk of predation and behavioural response in three anuran species: influence of tadpole size and predator type

Many species alter their activity, microhabitat use, morphology and life history in response to predators. Predation risk is related to predator size and palatability of prey among others factors. We analyzed the predation risk of three species of tadpoles that occur in norwestern Patagonia, Argentina: Pleurodema thaul, Pleurodema bufoninum and Rhinella spinulosa. We sampled aquatic insect predators in 18 ponds to determine predator–tadpole assemblage in the study area. In laboratory conditions, we analysed the predation rate imposed by each predator on each tadpole species at different tadpole sizes. Finally, we tested whether tadpoles alter their activity in the presence of chemical and visual cues from predators. Small P. thaul and P. bufoninum tadpoles were the most vulnerable prey species, while small R. spinulosa tadpoles were only consumed by water bugs. Dragonflies and water bugs were the most dangerous tadpole predators. Small P. thaul tadpoles reduced their activity when they were exposed to all predators, while large tadpoles only reduced the activity in the presence of large predators (dragonfly larvae and water bugs). Small P. bufoninum tadpoles reduced the activity when they were exposed to beetle larvae and dragonfly larvae, while large tadpoles only reduced activity when they were exposed to larger predators (water bugs and dragonfly larvae). R. spinulosa tadpoles were the less sensitive to presence of predators, only larger tadpoles responded significantly to dragonfly larvae by reducing their activity. We conclude that behavioural responses of these anuran species were predator-specific and related to the risk imposed by each predator.     

Antipredator Behavior of American Bullfrogs (Lithobates catesbeianus) in a Novel Environment

Invasive species capable of recognizing potential predators may have increased establishment rates in novel environments. Individuals may retain historical predator recognition and invoke innate responses in the presence of taxonomically or ecologically similar predators, generalize antipredator responses, or learn to avoid risky species in novel environments. Invasive amphibians in aquatic environments often use chemical cues to assess predation risk and learn to avoid novel predators via direct experience and/or associated chemical cues. Ontogeny may also influence recognition; experience with predators may need to occur at certain developmental stages for individuals to respond correctly. We tested predator recognition in invasive American bullfrog ( Lithobates catesbeianus) tadpoles that varied in experience with fish predators at the population and individual scale. We found that bullfrog tadpoles responded to a historical predator, largemouth bass ( Micropterus salmoides), only if the population was locally sympatric with largemouth bass. Individuals from a population that did not co‐occur with largemouth bass did not increase refuge use in response to either largemouth bass chemical cues alone or chemical cues with diet cues (largemouth bass fed bullfrog tadpoles). To test whether this behavioral response was generalized across fish predators, we exposed tadpoles to rainbow trout ( Oncorhynchus mykiss) and found that tadpoles could not recognize this novel predator regardless of co‐occurrence with other fish species. These results suggest that environment may be more important for predator recognition than evolutionary history for this invasive species, and individuals do not retain predator recognition or generalize across fish predators.     

Activity of Sphaerotheca breviceps tadpoles in response to chemical cues of the predaceous tadpoles Hoplobatrachus tigerinus

Tadpoles of Sphaerotheca breviceps raised in the laboratory from the egg stage, and hence lacking prior experience of a predator or its odors, were tested to examine their responses to a predator’s (tadpoles of Hoplobatrachus tigerinus) water-borne chemical cues. The stimulus solution was obtained following 24 h of rearing tadpoles of H. tigerinus (one tadpole per 200 mL water) that were not fed during this period. Upon exposure to the stimulus solution the activity of S. breviceps tadpoles decreased by about 90% within 5 min. Their resting period increased significantly over baseline activity, whereas the swimming period, distance traversed, and swimming spurts declined. However, whenever a test tadpole moved, its swimming velocity was high in response to stimulus solution. The antipredatory responses declined with increase in time of storage of the stimulus solution, indicating decay of the predator’s chemical cues. The findings suggest that (1) antipredator defense strategies of S. breviceps do not require prior experience of predators, (2) the predator’s chemical cues are labile in nature, and (3) the response of prey tadpoles to such cues is similar to reported behavior of anuran tadpoles in response to real predators and alarm cues.     

The ecological role of chemical stimuli for the zooplankton: predator-induced morphology in Daphnia

Summary Numerous adaptive predator-induced responses occurred when eight clones representing seven Daphnia (Crustacea: Cladocera) species were tested against three common predators: fourth instar larval phantom midge Chaoborus americanus, adult backswimmer Notonecta undulata, and small sunfish Lepomis macrochirus. The predators were confined within small mesh bags, suggesting that the signal for induction is chemical. The induced responses included longer tail spines, longer heads, smaller bodies, increased egg clutches, and decreased lipid reserves. Each Daphnia species responded to each of the three predators in a unique manner. Induced responses in the above characters showed no significant association. The induced morphological changes are generally consistent with current theories of what is an adaptive response for the various sizes of Daphnia exposed to tactile and visual predators. The abundance of induced responses in these experiments suggests that predator-induced responses are a widespread and ecologically important phenomenon of the freshwater zooplankton.     

Embryonic and larval defensive responses of agile frog (Rana dalmatina) to alien crayfish

Red swamp crayfish Procambarus clarkii, a widespread invasive alien crayfish, represents a serious threat for several freshwater species, including amphibians, which are declining at a global scale. As a shared coevolutionary history is the main factor determining the emergence of antipredator responses, Anuran tadpoles may not be able to cope effectively with this introduced predator. We performed two experiments to assess agile frog's (Rana dalmatina) defensive responses to both P. clarkii and native dragonfly larvae (Anax imperator). First, we conditioned embryos (collected from two ponds 30 km away from each other) with predators’ chemical cues to explore possible variation in hatching time caused by predation risk. In the second experiment, to evaluate how predators’ diet affects tadpole behavior, we conditioned tadpoles for a 5‐week period with cues from tadpole‐fed and gammarid‐fed predators and recorded behavioral and morphological responses. Embryos did not alter hatching time in the presence of any predator cue, while tadpoles from both populations strongly reduced activity and visibility when raised in the presence of tadpole‐fed dragonfly larvae. Morphological changes were less straightforward and were induced only in one population, for which broader tails and a slight increase in body size of tadpoles exposed to tadpole‐fed predators were observed. The lack of defensive responses in crayfish‐exposed tadpoles suggests that the spreading of this invasive species in agricultural lowlands of northern Italy may represent a further threat to their conservation.     

Do Experience and Body Size Play a Role in Responses of Larval Ringed Salamanders,Ambystoma annulatum,to Predator Kairomones? Laboratory and Field Assays

Prey may experience ontogenetic changes in vulnerability to some predators, either because of changes in morphology or experience. If prey match their level of antipredator behavior to the level of predatory threat, prey responses to predators should reflect the appropriate level of threat for their stage of development. For larval salamanders, responses to predators may change with body size because larger larvae are less vulnerable to predation by gape‐limited predators or because fleeing responses by large salamanders may be more effective than for smaller salamanders. In a field experiment, small larval ringed salamanders, Ambystoma annulatum, responded to chemical stimuli (‘kairomones’) from predatory newts, Notophthalmus viridescens, with an antipredator response (decreased activity). Laboratory‐reared larvae decreased their activity following exposure to newt kairomones, indicating that larval ringed salamanders do not require experience with newts to recognize them as predators. In both experiments, larvae distinguished between chemical stimuli from newts and stimuli from tadpoles (non‐predators) and a blank control. In a third experiment, field‐caught (experienced) larvae showed a graded response to newt kairomones based on their body size: small larvae tended to decrease their activity while larger larvae showed no change or an increase in activity. This graded response was not observed for neutral stimuli, indicating that it is predator‐specific. Therefore, ringed salamander larvae exhibit threat‐sensitive ontogenetic changes in their response to chemical stimuli from predatory newts.     

Understanding the toad code: Behavioural responses of cane toad (Chaunus marinus) larvae and metamorphs to chemical cues

Abstract Larvae of many anuran taxa display strong behavioural responses to chemical cues, including alarm signals from injured conspecific tadpoles. We exposed tadpoles and metamorphs from an Australian population of the invasive cane toad (Chaunus[Bufo] marinus) to a range of chemical stimuli and quantified their responses both in the laboratory and in the field. Filtered fluids containing scent cues from crushed conspecifics elicited strong avoidance from tadpoles, whereas other cues (e.g. scent of food, of native‐range fish or urodele predators, and thermal stimuli) did not. Apparent aggregation of tadpoles in response to scent cues proved to be an artifact of tank design, and was an indirect consequence of avoidance of those cues. Field trials confirmed that free‐ranging toad tadpoles and metamorphs avoided chemical cues from crushed conspecifics, suggesting that the chemicals inducing this response might provide an opportunity to develop targeted control methods for this invasive species.     

Chemical cues from multiple predator-prey interactions induce changes in behavior and growth of anuran larvae

Chemical signals are used as information by prey to assess predation risk in their environment. To evaluate the effects of multiple predators on prey growth, mediated by a change in prey activity, I exposed small and large bullfrog (Rana catesbeiana) larvae (tadpoles) to chemical cues from different combinations of bluegill sunfish (Lepomis macrochirus) and larval dragonfly (Anax junius) predators. Water was regularly transferred from predation trials (outdoor experiment) to aquaria (indoor experiment) in which activity and growth of tadpoles was measured. The highest predation mortality of small bullfrog larvae in the outdoor experiment was due to Anax, and it was slightly lower in the presence of both predators, probably resulting from interactions between predators. There was almost no mortality of prey with bluegill. The activity and growth of small bullfrog larvae was highest in the absence of predators and lowest in the presence of Anax. In the presence of bluegill only, or with both predators, the activity and growth of small bullfrog tadpoles was intermediate. Predators did not affect large tadpole activity and growth. Regressing mortality of small bullfrog tadpoles against activity and growth of bullfrog tadpoles revealed a significant effect for small bullfrog larvae but a non-significant effect for large bullfrog larvae. This shows that the response of bullfrog tadpoles to predators is related to their own body size. The experiment demonstrates that chemical cues are released both as predator odor and as alarm substances and both have the potential to strongly alter the activity and growth of prey. Different mechanisms by which chemical cues may be transmitted to species interactions in the food web are discussed. Received: 28 June 1999 / Accepted: 15 November 1999     

Predator-Induced Changes in Metabolism Cannot Explain the Growth/Predation Risk Tradeoff

Defence against predators is usually accompanied by declining rates of growth or development. The classical growth/predation risk tradeoff assumes reduced activity as the cause of these declines. However, in many cases these costs cannot be explained by reduced foraging effort or enhanced allocation to defensive structures under predation risk. Here, we tested for a physiological origin of defence costs by measuring oxygen consumption in tadpoles (Rana temporaria) exposed to predation risk over short and long periods of time. The short term reaction was an increase in oxygen consumption, consistent with the “fight-or-flight” response observed in many organisms. The long term reaction showed the opposite pattern: tadpoles reduced oxygen consumption after three weeks exposure to predators, which would act to reduce the growth cost of predator defence. The results point to an instantaneous and reversible stress response to predation risk. This suggests that the tradeoff between avoiding predators and growing rapidly is not caused by changes in metabolic rate, and must be sought in other behavioural or physiological processes.     

Behavioural response of bullfrog tadpoles to chemical cues of predation risk are affected by cue age and water source

When confronted by signals of predators presence, many aquatic organisms modify their phenotype (e.g., behaviour or morphology) to reduce their risk of predation. A principal means by which organisms assess predation risk is through chemical cues produced by the predators and/or prey during predation events. Such responses to predation risk can directly affect prey fitness and indirectly affect the fitness of species with which the prey interacts. Accurate assessment of the cue will affect the adaptive nature, and hence evolution, of the phenotypic response. It is therefore, important to understand factors affecting the assessment of chemical cues. Here I examined the effect of the age of chemical cues arising from an invertebrate predator, a larval dragonfly (Anax junius), which was fed bullfrog tadpoles, on the behavioural response (activity level and position) of bullfrog tadpoles. The bullfrog response to chemical cues declined as a function of chemical cue age, indicating the degradation of the chemical cue was on the order of 2–4 days. Further, the decay occurred more rapidly when the chemical cue was placed in pond water rather than well water. These results indicate a limitation of the tadpoles to interpret factors that affect the magnitude of the chemical cue and hence accurately assess predation risk. These findings also have implications for experimental design and the adaptation of phenotypic responses to chemical cues of predation risk.     

Behavioural and life history responses to predation risk by common frog tadpoles exposed to two predators during ontogeny

The presence of predators can induce changes in both the morphology and behaviour of Anuran larvae, affecting both their size and developmental stage at metamorphosis and, consequently, the fitness of adult individuals. Tadpoles have been shown to be capable of finely tuning their defensive responses according to the actual risk perceived, which is expected to vary according to the prey-to-predator size ratio. In this study, we exposed common frog (Rana temporaria) tadpoles (Gosner stages 28–30), for a period of 2 weeks, to the non-lethal presence of dragonfly larvae (Anax imperator) and backswimmers (Notonecta glauca). In such a narrow window of time, we expected behavioural responses to be similar for both predators and exposure to predation risk to have negligible effects on tadpole development and weight. Overall, tadpoles increased hiding behaviour and were less active when predators were present in the experimental mesocosms, but behavioural responses were constrained to the early phase of the ontogeny and were no longer used when tadpoles reached a threshold size. Developmental rate slightly slowed down for predator treatments in comparison to controls, possibly as a consequence of energetic investment in unrecorded morphological defences. Although variation in laboratory conditions and protocols makes it hard to compare the results of different experiments, our results contribute to verify the consistency of behavioural responses in Anuran larvae.     

Chemical defense of toad tadpoles under risk by four predator species

Many organisms use inducible defenses as protection against predators. In animals, inducible defenses may manifest as changes in behavior, morphology, physiology, or life history, and prey species can adjust their defensive responses based on the dangerousness of predators. Analogously, prey may also change the composition and quantity of defensive chemicals when they coexist with different predators, but such predator‐induced plasticity in chemical defenses remains elusive in vertebrates. In this study, we investigated whether tadpoles of the common toad (Bufo bufo) adjust their chemical defenses to predation risk in general and specifically to the presence of different predator species; furthermore, we assessed the adaptive value of the induced defense. We reared tadpoles in the presence or absence of one of four caged predator species in a mesocosm experiment, analyzed the composition and quantity of their bufadienolide toxins, and exposed them to free‐ranging predators. We found that toad tadpoles did not respond to predation risk by upregulating their bufadienolide synthesis. Fishes and newts consumed only a small percentage of toad tadpoles, suggesting that bufadienolides provided protection against vertebrate predators, irrespective of the rearing environment. Backswimmers consumed toad tadpoles regardless of treatment. Dragonfly larvae were the most voracious predators and consumed more predator‐naïve toad tadpoles than tadpoles raised in the presence of dragonfly cues. These results suggest that tadpoles in our experiment had high enough toxin levels for an effective defense against vertebrate predators even in the absence of predator cues. The lack of predator‐induced phenotypic plasticity in bufadienolide synthesis may be due to local adaptation for constantly high chemical defense against fishes in the study population and/or due to the high density of conspecifics.     

Predator Avoidance and Alarm-response Behaviour in Kin-discriminating Tadpoles (Rana cascadae)

When captured by predators, the tadpoles of some species of frogs and toads may release an alarm substance that alters the behaviour of conspecifics. Such ‘alarm response’ behaviour has been proposed as a potential mechanism whereby related conspecifics may ‘warn’ relatives of a predator's presence and thus, improve their inclusive fitness. We examined predator avoidance and alarm response behaviour in tadpoles of the Cascades frog (Rana cascadae) and tested whether such behaviour is influenced by kinship factors. Tadpoles reduced activity when in the presence of a predatory newt (Taricha granulosa). Individuals in sibling groups were more active than both solitary tadpoles and individuals in mixed groups of siblings and nonsiblings. However, we found no evidence of an alarm response in R. cascadae. Behaviour of tadpoles in groups exposed only to predators was not different from that of tadpoles in groups exposed to predators plus crushed conspecifics. Tadpoles in groups exposed to crushed tadpoles were as active as tadpoles in groups exposed to water controls, and some test individuals fed upon the dead tadpoles. Thus, while R. cascadae tadpoles reduce activity in response to newt predators, crushed tadpoles appear to initiate a feeding response rather than an alarm response as has been previously proposed.     

Multiple predator effects on size-dependent behavior and mortality of two species of anuran larvae

This study examined the effects of multiple predators on size‐specific behavior and mortality of two species of anuran larvae. Particularly, we focused on how trait changes in predators and prey may be transmitted to other species in the food web. In laboratory experiments, we examined the effects of bluegill sunfish, Lepomis macrochirus, and the odonate larva Anax junius on behavior and mortality of tadpoles of the bullfrog, Rana catesbeiana, and the green frog R. clamitans. Experiments were conducted with predators alone and together to assess effects on behavior and mortality of the tadpoles. The experiments were replicated on five size classes of the tadpoles to evaluate how responses varied with body size.
Predation rates by Anax were higher on bullfrogs than on green frogs, and both bullfrogs and green frogs suffered greater mortality from Anax than from bluegill. Bluegill only consumed green frogs. Predation rates by both predators decreased with increasing tadpole size and decreased in the non‐lethal (caged) presence of the other predator. Both anuran larvae decreased activity when exposed to predators. Bullfrogs, however, decreased activity more in the presence of Anax than in the presence of bluegill, whereas green frogs decreased activity similarly in the presence of both predators. The largest size class of green frogs, but not of bullfrogs, exhibited spatial avoidance of bluegill. These responses were directly related to the risk posed by the different predators to each anuran species. Anax activity (speed and move frequency) also was higher when alone than in the non‐lethal presence of bluegill. We observed decreased predation rate of each predator in the non‐lethal presence of the other, apparently caused by two different mechanisms. Bluegill decreased Anax mortality on tadpoles by restricting the Anax activity. In contrast, Anax decreased bluegill mortality on tadpoles by reducing tadpole activity. We discuss how the activity and spatial responses of the tadpoles interact with palatability and body size to create different mortality patterns in the prey species and the implications of these results to direct and indirect interactions in this system.     

Alarm signals in Daphnia?

Daphnia magna can respond to chemical cues from freshly crushed conspecifics with various behavioural reactions. A shift in vertical distribution towards the bottom, the formation of aggregations and direct escape responses can all be induced by water-borne signals released from crushed Daphnia. The pattern and strength of the first two behavioural responses (i.e. the persistent tendency to occupy deeper strata in the experimental columns and to stay within patches) indicate that Daphnia perceive the signal from crushed conspecifics as nonspecific information, not necessarily associated with any particular kind of danger from either vertebrate or invertebrate predators. The adaptive value and possible costs associated with performing these two behavioural reactions are discussed. The adaptive value of the induced escape response was directly tested: Daphnia which had experienced the presence of a cue from crushed conspecifics avoided attacks by common bream more efficiently than naive Daphnia. The recognition of the signal originating from crushed conspecifics can be especially adaptive in encounters with unfamiliar predators and with predators that undergo ontogenetic shifts in their diet. Under natural conditions, the combination of such a signal with a predator cue can, very reliably, advertise the local scale of the predatory impact. Received: 10 October 1996 / Accepted: 20 May 1997     

Field Response of Tadpoles to Conspecific and Heterospecific Alarm

Many organisms use chemical cues from a variety of sources to mediate predator avoidance. Response to heterospecific alarm cues has been demonstrated for tadpoles within but not among taxa and alarm response behavior has seldom been examined under field conditions. This study examined the response of three sympatric amphibian larvae and predaceous larval Dytiscus sp. (diving beetle) to damage-release signals in natural ponds by using capture rates from treated funnel traps as an index of larval behavior. Hyla regilla (Pacific tree frog) tadpoles avoided traps treated with either crushed conspecifics or with Rana aurora (red-legged frog) tadpoles but the larger ranids and Ambystoma macrodactylum (long-toed salamander) did not respond to either treatment. H. regilla tadpoles were likely susceptible to any potential predators of ranid tadpoles in these ponds and this result is consistent with the hypothesis that a response to heterospecific alarm occurs in sympatric prey with shared predators.