The uneasy coexistence between Carpet Pythons and Cane Toads

Abstract

We describe a case of a free-ranging Carpet Python Morelia spilota consuming a toxic Cane Toad Rhinella marina, and dying as a result. Such an encounter would not be surprising at the toad invasion front, where predators first confront this novel prey type. However, the encounter we describe occurred at a site near Darwin where toads have been present for fifteen years. Other reports suggest that the behaviour we observed occurs across the snake’s range. Lethal ingestion of toads has been suggested to threaten the viability of populations of Carpet Pythons, but paradoxically, our surveys at this site reveal a twofold increase in abundance of Carpet Pythons since the arrival of toads. Toad invasion likely has favoured pythons by reducing the abundance of large monitor lizards, that are both predators and competitors of Carpet Pythons. That advantage has outweighed occasional cases where a snake is fatally poisoned by consuming a toad. Thus, the overall impact of Cane Toads on Carpet Pythons (and likely, other predator species) is a balance between direct costs and indirect benefits. Negative impacts on individuals may not necessarily translate to a negative impact on the species.