Effect of fish species and size on the antipredator behavior of the San Marcos salamander (Eurycea nana)

Background/Question/Methods

Both effective and efficient predator avoidance behaviors are essential for the persistence of prey with predators. Prey individuals exhibiting effective avoidance are able to recognize predatory stimuli and respond in a manner that reduces the probability of predation. However, prey that exhibit antipredator behavior in response to less threatening stimuli (e.g., non- or gape-limited predators) may accrue unnecessary costs because these behaviors detract from time that could be spent foraging or mating. We examined the effect of fish species and fish size on the antipredator behavior of the federally threatened San Marcos salamander (Eurycea nana), a neotenic (obligate aquatic) species endemic to the headwaters of the San Marcos River, Hays Co., Texas. We exposed predator-naïve (captive-reared), adult salamanders to 50 ml of chemical stimuli from either a small (SL < 50 mm) or large (SL > 80 mm) low-risk (Cyprinella venusta) or high-risk (Lepomis cyanellus) predator or to a control of a small, non-predatory prey-guild member (Etheostoma fonticola). Salamanders are commonly found along the benthos where L. cyanellus often feeds, while C. venustais an omnivorous, surface-feeding species.

Results/Conclusions

First, we compared responses to predators to our non-predator control treatment using a non-parametric Steel's test. Responses to both small and large C. venusta did not differ from the control. We then excluded the control from further analyses. Using a 2-factor ANOVA on rank-transformed data, we found that the effects of both predator species (p = 0.006) and size (p = 0.005) were significant with no significant interaction (p = 0.955). As expected, the antipredator response to predatory fish (L. cyanellus) was stronger than the response to the non-predatory fish (C. venusta). Unexpectedly, salamanders significantly reduced activity (antipredator behavior) more in response to smaller rather than larger fish. Small (gape-limited) fish are unable to consume adult salamanders and antipredator behavior seems unnecessary and costly. The exact reason for this is uncertain; it is possible that ecological relationships between fish and salamanders were different prior to anthropogenic alterations to the habitat Additionally, due to the capacity for plasticity in these salamanders, it is also possible that this stronger response to gape-limited predators may represent an ontogenetic holdover resulting from a lifetime in captivity. Ultimately, complex interactions between fish and salamanders in this system exist and need to be explored further.