Mapping the spread of invasive cane toads (Rhinella marina) in southern Australia

By fatally poisoning apex predators, invasive cane toads (Rhinella marina) have modified ecosystems across much of Australia. Most research on their invasion has been conducted in the tropics, with the southern front of their range expansion largely overlooked. To address that knowledge gap, I assembled multiple datasets to characterise the historical spread of toads through north-eastern New South Wales in order to clarify factors that might influence routes and rates of dispersal. My pilot studies at the range edge suggest that visual and acoustic surveys are as effective as eDNA-based surveys. Expansion of the toads’ range in NSW has occurred through the establishment of satellite populations and through growth of the range core. Overall rates of spread have been far lower than on the tropical front, and in some decades the area occupied by toads appears to have declined rather than expanded. Rates of spread have accelerated to the south, but westward expansion has slowed. Toad range expanded most rapidly in decades with dry, warm weather conditions, suggesting that predicted future changes to climate could increase or decrease rates of toad spread. Understanding the historical patterns of toad invasion in NSW may clarify priority areas for monitoring and control programs.