Effects of land-use change and elevation on endemic shrub frogs in a biodiversity hotspot

Abstract

Agroforestry, often promoted as a sustainable agriculture practice, is rapidly expanding, often at the cost of primary tropical forests. While agroforestry negatively impacts amphibian diversity, its effects on population demography, microhabitat, use and body condition are relatively understudied. This information is crucial for determining and promoting amphibian-friendly land-use practices. We compared habitats, population densities, microhabitat use and body condition of two endemic species of shrub frogs (Pseudophilautus amboli and Raorchestes bombayensis) across (1) elevations (low- and high-elevation forests) and (2) land-use categories (cashew, rubber and low-elevation forests) in the northern part of the Western Ghats Biodiversity Hotspot. Using distance sampling, we demonstrated that the abundances of the two shrub frog species differed across elevation categories, with P. amboli more common in low-elevation forests and R. bombayensis more prevalent in high-elevation forests. Both species of frogs exhibited extremely skewed, male-biased sex ratios, with three females for 100 males. P. amboli had lower densities and poor recruitment and exhibited altered microhabitat use in cashew plantations compared to low-elevation forests. Although adult male P. amboli densities in rubber were similar to those in low-elevation forests, they exhibited altered microhabitat use and smaller body sizes than in forests, indicating poor body condition. We demonstrate the differential impacts of agroforestry types on shrub frogs. We also demonstrate that distance sampling can be a useful tool for population monitoring of shrub frogs, which comprise almost 25% of the anuran diversity in the Western Ghats. There is a need to identify the drivers of extremely skewed sex ratios, which make these species vulnerable to population crashes. Given the recent downlisting of the two focal species to Least Concern, we advocate for their uplisting to at least Near Threatened status considering their patchy distribution, negative impacts of rapidly expanding agroforestry plantations and extremely skewed sex ratios.