Coexistence of fish, frogs, and fly-fishers: Can't we all just get along?

摘要

Introduced species are one of the leading causes of human induced environmental change worldwide, but due to the political and practical difficulties in eradicating invaders, it is often more feasible to study how native species coexist with them. In this dissertation, I studied ways in which native organisms coexist with and adapt to introduced species, using the case study of the Cascades frog (Rana cascadae), and trout (Oncorhynchus spp, and Salvelinus spp.) introduced to high mountain lakes for recreational fisheries. Habitat heterogeneity commonly contributes to predator-prey coexistence. Therefore, in the first chapter of my dissertation, I surveyed habitat factors that allows Rana cascadae to coexist with trout. I identified large, vegetated shallow areas, nearby breeding populations, and the presence of western toads as the most important correlates of co-occurrence between R. cascadae and trout. Because other amphibians that are allopatric with fish do not respond to fish chemical cues, in the second chapter of my dissertation I tested whether R. cascadae larvae were changing their behavior in response to cues from this new predator. I collected frog eggs from lakes with and without trout and performed behavior assays on the tadpoles once they hatched. All populations, even those from fishless lakes, increased refuge use dramatically when exposed to fish chemical cues. I also found evidence consistent with evolution of a constitutive increase in antipredator behaviors in the absence of fish, but weaker anti-predator behaviors in the presence of fish for populations that co-occur with fish. To explore the human component of my study system, I conducted a survey of the visitors to my study site. This survey found about 25% of people were fishing in the area, but less than 1% felt that fishing was the most important part of their trip, indicating less conflict between fisheries management and amphibian conservation than previously assumed. In the final component of my dissertation, I created a stochastic stage-structured metapopulation model of how the presence of habitat patches containing novel predators may act as ecological traps for naive prey. The model demonstrated that some dispersal toward an ecological trap caused greater metapopulation growth than total preference for a higher quality patch due to bet-hedging. Together, my dissertation chapters demonstrate potential for "Reconciliation Ecology" in the anthropogenically altered communities of wilderness lakes; I identify potential spatial and evolutionary mechanisms by which introduced trout and native amphibians may coexist. Enhanced coexistence would improve this novel ecosystem by reversing declines of native biodiversity while maintaining recreational opportunities.