Accessible habitat and wetland structure drive occupancy dynamics of a threatened amphibian across a peri-urban landscape

Abstract

Populations of aquatic-breeding amphibians are declining from habitat loss, fragmentation and degradation. Identifying how populations are affected by landscape barriers such as roads is essential for conservation and requires understanding the processes underpinning species occupancy in fragmented landscapes. Here, I assessed relationships between the occupancy dynamics of the threatened green and golden bell frog (Litoria aurea) and accessible habitat; i.e., the area of breeding and non-breeding habitat around a wetland that can be reached by an amphibian without having to cross a highway. I hypothesised that relationships between occupancy and accessible habitat would be stronger than relationships with the area of extant native vegetation, road density or distance to the highway. I also examined relationships with local habitat variables over a three-year period. Relationships with accessible habitat were stronger and more certain in explaining L. aurea occupancy and colonisation than other landscape variables. Accessible habitat was positively associated with wetland occupancy, which suggests the highway is having a barrier effect on the population. There was a positive relationship between road density and the probability of local extinction. Occupancy rates at highway compensatory ponds increased from near-zero within six months of pond construction, to >30% after 12 months. There was a negative relationship between local extinction and aquatic vegetation cover, highlighting the importance of habitat structure for L. aurea. Urban planners should consider accessible habitat when managing amphibian species in rapidly urbanising landscapes, so that all habitats required throughout a species’ life cycle are protected.