THE INVASION ECOLOGY OF THE TOAD BUFO-MARINUS - FROM SOUTH-AMERICA TOAUSTRALIA

Mark-recapture studies indicate that Bufo marinus populations introduc ed into Australia tend to attain densities much higher than those repo rted in native habitats in South America. Moreover, its high rate of s pread into northern Australia is raising concerns about the local faun a. The major ecological factors contributing to the observed differenc es in density are unknown. A population model based on empirical data from both continents was derived to explore the relationship between t he life history parameters and population densities of this species, a nd to identify those parameters most likely to explain the differences in densities observed between continents. Model predictions seem cons istent with the empirical data. The model predicted equilibrium densit ies in Australia one order of magnitude higher than those reported in South America. Moreover, a sensitivity analysis showed that adult equi librium densities were much more sensitive to variations in adult surv ival than to variations in any of the other parameters at high densiti es. Coincidentally, it is adult survival for which the biggest differe nces between continents have been detected, suggesting that the higher toad densities reported in Australia are likely to be the result of h igher adult survival in that continent. On the other hand, the high se nsitivity of adult equilibrium densities to adult survival also has im portant implications for control of this species in Australia.