The Invasion Ecology of the Toadbufo Marinus:from South America to Australia

Mark–recapture studies indicate that Bufo marinus populations introduced into Australia tend to attain densities much higher than those reported in native habitats in South America. Moreover, its high rate of spread into northern Australia is raising concerns about the local fauna. The major ecological factors contributing to the observed differences in density are unknown. A population model based on empirical data from both continents was derived to explore the relationship between the life history parameters and population densities of this species, and to identify those parameters most likely to explain the differences in densities observed between continents. Model predictions seem consistent with the empirical data. The model predicted equilibrium densities in Australia one order of magnitude higher than those reported in South America. Moreover, a sensitivity analysis showed that adult equilibrium densities were much more sensitive to variations in adult survival than to variations in any of the other parameters at high densities. Coincidentally, it is adult survival for which the biggest differences between continents have been detected, suggesting that the higher toad densities reported in Australia are likely to be the result of higher adult survival in that continent. On the other hand, the high sensitivity of adult equilibrium densities to adult survival also has important implications for control of this species in Australia.