Restoring breeding habitat for Giant Bullfrogs (Pyxicephalus adspersus) in South Africa

Abstract

Habitat fragmentation and transformation arising from urbanisation are leading causes of frog population declines. Artificial wetlands are sometimes used in remediation to minimise biodiversity loss in urban landscapes, but little is known about the specific habitat requirements of frog species for breeding. The aim of our study was to identify pan characteristics that promote Giant Bullfrog (Pyxicephalus adspersus) breeding success, in order to improve artificial wetland design. African Bullfrogs breed in ephemeral pans and are currently listed by the International Union for Conservation of Nature (IUCN) regionally as ‘Near Threatened’. Most suitable bullfrog habitat has been transformed in the highly urbanised province of Gauteng, South Africa. We conducted this study in the Total Petroport N14 Biodiversity Reserve (Gauteng Province), which is an artificial wetland complex created in 2006 specifically for the conservation of bullfrog populations. Tadpole numbers and froglet recruitment were compared to the physical characteristics and water quality of 12 pans over two breeding seasons. Total dissolved solids (TDS) in pan water were weakly correlated with tadpole number. Survival to metamorphosis was significantly higher in pans which had been lined and as a result had longer hydroperiod. Frog recruitment, however, was not related to any of the measured physical characteristics of the pans. Thus, bullfrogs appear to be non-selective in their choice of breeding sites, and breeding success appears to largely depend on stochastic events, such as drying of pans. Confounding factors such as proximity to human activity may also impact breeding success. We conclude that a wide variety of artificial pans can adequately ameliorate negative impacts of land transformation on bullfrog recruitment.