Abstract. Over the last two decades, numerous studies have shown that alien predators contributed to amphibian population declines. Both experimental studies and correlative field surveys implicated alien species of fish, bullfrogs and crayfish as major contributors to amphibian population decline, and in some instances local extinction. Additional studies have demonstrated that alien predators also caused long‐term changes in aquatic communities. Recent studies have examined the feasibility of removing alien predators, and provide some evidence that amphibian populations can recover. Applying information gained from past studies to the recovery of amphibian populations will be the challenge of future studies. International, national and local policies that regulate alien predators should be based largely on the body of scientific evidence already in the literature. Scientists need to be more involved with policy‐makers to most effectively change laws that regulate alien predators.

Larvae of the California newt (Taricha torosa) exhibit striking predator‐avoidance behavior, escaping to refuges in response to a chemical cue from cannibalistic adults. In laboratory flow‐tank experiments, stream water collected near free‐ranging adults induced hiding responses in 100% of the larvae tested. Solutions prepared by bathing adults (in field and laboratory) also evoked strong hiding behaviors. Insensitive to adult feeding status (fed or starved), and clearly not an excretory product, the chemical cue was released from adult skin (i.e., in swabs of adult backs, sides, and bellies). Tetrodotoxin (TTX) was found in skin swabs of adults and in bathwater at 1 × 10−7 mol/L using reversed‐phase high‐pressure liquid chromatography (HPLC). Concentrations of 1 × 10−7 to 1 × 10−9 mol/L TTX standard, and equivalent dilutions of bathwater, triggered hiding behaviors in larvae, with no subsequent sublethal toxicity. The presence of TTX‐sensitive cells within larval olfactory epithelium was confirmed by behavioral experiments and electrophysiological recordings. In contrast, larvae did not hide in response to two other, structurally mimetic compounds (saxitoxin and μ‐conotoxin GIIIB). Ontogenetically, larval behavioral responses to TTX and bathwater were strongest during weeks 3–5, diminishing to nil during week 7. No longer susceptible to adult cannibalism, larval indifference to the cue coincided with their ability to climb out of water and onto land. Thus, newt larvae escape cannibalism by detecting a poison (TTX) well known as a chemical defense for conspecific adults. Eliciting a behavioral response in one case and inhibiting neural activity in the other, this compound results in opposing physiological effects, with avoiding predation as the common goal. Accordingly, TTX joins a select group of keystone molecules, each having critical, but different, ecological consequences at multiple trophic levels. The unique combination of bioactive properties makes a compelling case for asymmetrical selection as a force driving the evolution of adult–larval trophic interactions.

Neuroecology unifies principles from diverse disciplines, scaling from biophysical properties of nerve and muscle cells to community-wide impacts of trophic interactions. Here, these principles are used as a common fabric, woven from threads of chemosensory physiology, behavior, and population and community ecology. The "keystone species" concept, for example, is seminal in ecological theory. It defines a species whose impacts on communities are far greater than would be predicted from its relative abundance and biomass. Similarly, neurotoxins could function in keystone roles. They are rare within natural habitats but exert strong effects on species interactions at multiple trophic levels. Effects of two guanidine alkaloids, tetrodotoxin (TTX) and saxitoxin (STX), coalesce neurobiological and ecological perspectives. These molecules compose some of the most potent natural poisons ever described, and they are introduced into communities by one, or only a few, host species. Functioning as voltage-gated sodium channel blockers for nerve and muscle cells, TTX and STX serve in chemical defense. When borrowed by resistant consumer species, however, they are used either in chemical defense against higher order predators or for chemical communication as chemosensory excitants. Cascading effects of the compounds profoundly impact community-wide attributes, including species compositions and rates of material exchange. Thus, a diverse array of physiological traits, expressed differentially across many species, renders TTX and STX fully functional as keystone molecules, with vast ecological consequences at multiple trophic levels.

Many animals, plants, and microorganisms are harmed by ultraviolet‐B radiation. In particular, several members of class amphibia are negatively affected by exposure to ultraviolet‐B radiation. Exposure to ultraviolet‐B radiation can cause death or various types of sublethal damage in amphibians. One mechanism to lessen the effect of harmful ultraviolet‐B radiation is to limit exposure to sunlight behaviorally. Few studies have examined the behavioral sensitivity of adult amphibians to ultraviolet‐B radiation. Using both field experiments and field observations, we found that two species of diurnal poison‐dart frogs in Costa Rica (Dendrobates pumilio, D. auratus) consistently preferred areas in the field and within experimental testing chambers that offered low levels of ultraviolet‐B radiation. In field observations, vocalizing D. pumilio were found at locations with significantly lower levels of ambient ultraviolet‐B compared to random locations throughout their natural habitat. Ultraviolet‐B avoidance behavior may be an important behavioral response for tropical frogs in light of recent evidence suggesting a significant increase in the levels of ambient ultraviolet‐B radiation in the tropics over the past decade.

SUMMARY Animal perception of chemosensory cues is a function of ecological context. Larvae of the California newt (Taricha torosa), for example, exhibit predator-avoidance behavior in response to a chemical from cannibalistic adults. The poison tetrodotoxin (TTX), well known as an adult chemical defense, stimulates larval escape to refuges. Although they are cannibals,adult newts feed preferentially on worms (Eisenia rosea) over conspecific young. Hence, larval avoidance reactions to TTX are suppressed in the presence of odor from these alternative prey. The free amino acid,arginine, is abundant in fluids emitted by injured worms. Here, we demonstrate that arginine is a natural suppressant of TTX-stimulated larval escape behavior. Compared to a tapwater control, larvae initiated vigorous swimming in response to 10–7 mol l–1 TTX. This excitatory response was eliminated when larval nasal cavities were blocked with an inert gel, but not when gel was placed on the forehead (control). In additional trials, a binary mixture of arginine and 10–7 mol l–1 TTX failed to induce larval swimming. The inhibitory effect of arginine was, however, dose dependent. An arginine concentration as low as 0.3-times that of TTX was significantly suppressant. Further analysis showed that suppression by arginine of TTX-stimulated behavior was eliminated by altering the positively-charged guanidinium moiety, but not by modifying the carbon chain, carboxyl group, or amine group. These results are best explained by a mechanism of competitive inhibition between arginine and TTX for common, olfactory receptor binding sites. Although arginine alone has no impact on larval behavior, it nevertheless signals active adult predation on alternative prey, and hence, reduced cannibalism risk.