Human traffic and habitat complexity are strong predictors for the distribution of a declining amphibian.

Rachel B Anderson,Paulo De Marco Júnior

doi:10.1371/journal.pone.0213426

Abstract

Invasive species and habitat modification threaten California's native pond-breeding amphibians, including the federally threatened California Red-legged Frog (Rana draytonii). The relative contributions of invasive species, including the American Bullfrog (Lithobates catesbeianus), and of habitat changes to these declines are disputed. I conducted a field study over several years in central California to examine the presence/absence of these two species at 79 breeding ponds to determine the predictive role for occupancy of factors including vegetation, pond characteristics, and measures of human activity. I used a boosted regression tree approach to determine the relative value of each predictor variable. Increased measures of human activity, especially proximity to trails and roads, were the best predictors for the absence of California Red-legged Frogs and California Newts. Historical factors and habitat conditions were associated with the extent and spread of the American Bullfrog. The extent and complexity of aquatic macrophytes and pond surface area were good predictors for the presence of these and other amphibian species. Surprisingly, invasive species played a relatively small role in predicting pond occupancy by the native species. These findings can inform conservation and restoration efforts for California Red-legged Frogs, which apparently persist best in small vegetated ponds in areas of low human disturbance.

Highlights

Invasive species represent a serious threat to the world’s biodiversity and to human activities [1,2]
Smaller surface area correlated with California Red-legged Frog presence (10.1% contribution to final boosted regression tree (BRT))
Two of the recorded vertebrate community species played predictive roles: California Red-legged Frogs were more likely to be found in ponds that were occupied by the California Newt (6.6%), and were less likely to be found in ponds with American Bullfrogs (3.7%)

Summary

Introduction

Invasive species represent a serious threat to the world’s biodiversity and to human activities [1,2]. They often have strong dispersal and reproduction abilities, such that established species introductions are frequently irreversible [3,4]. Their negative impacts can include decimating naïve native species through competition or predation. Some native species can mitigate these impacts by changing their behavior or habitat use in the presence of invasive predators. Habitat management and creation to enable this type of separation may provide the most feasible and cost-effective solution to promote native amphibian populations and counter

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Results

Conclusion