Effects of Vegetation Density on Habitat Suitability for the Endangered Green and Golden Bell Frog, Litoria aurea

摘要

Habitat offsetting is a conservation management regime used to preserve biodiversity when human development degrades areas inhabited by threatened species. Habitat suitability of a threatened species can vary temporally due to environmental changes. However, vegetation growth is rarely considered prior to mitigation attempts. The Green and Golden Bell Frog (Litoria aurea) is threatened by habitat loss and has been the subject of several habitat offsetting projects. Despite following recommended habitat templates, nearly all management projects have failed in creating a self-sustaining population. In this study, we examined differences in L. aurea occupancy among ponds with varied levels of vegetation density. We investigated extant occupancy patterns during a 2-y period among areas of sparse, medium, and dense vegetation growths. We also conducted a field manipulation experiment to determine differences in abundance and biotic and abiotic factors between waterbodies with either sparse (manually removed) or dense (naturally overgrown) vegetation covers. Occupancy by adult females and juveniles, but not adult males, differed among sites with different vegetation densities. Female occupancy was greater at sites with medium vegetation densities; whereas, juveniles occupied medium and densely vegetated waterbodies more frequently than sparsely vegetated waterbodies. We also detected differences in potential predators, aquatic competitors, food resources, and water quality between the sparsely and densely vegetated waterbodies. Our data should allow for better habitat management of future L. aurea compensatory projects, and underscores the importance of using both quantitative and qualitative pre-analysis to question temporal variances in habitat suitability prior to management offsets.