Behavioural flexibility allows an invasive vertebrate to survive in a semi-arid environment

Abstract

Plasticity or evolution in behavioural responses are key attributes of successful animal invasions. In northern Australia, the invasive cane toad (Rhinella marina) recently invaded semi-arid regions. Here, cane toads endure repeated daily bouts of severe desiccation and thermal stress during the long dry season (April-October). We investigated whether cane toads have shifted their ancestral nocturnal rehydration behaviour to one that exploits water resources during the day. Such a shift in hydration behaviour could increase the fitness of individual toads by reducing exposure to desiccation and thermal stress suffered during the day even within terrestrial shelters. We used a novel method (acoustic tags) to monitor the daily hydration behaviour of 20 toads at two artificial reservoirs on Camfield station, Northern Territory. Remarkably, cane toads visited reservoirs to rehydrate during daylight hours, with peaks in activity between 9.00 and 17.00. This diurnal pattern of rehydration activity contrasts with nocturnal rehydration behaviour exhibited by adult toads in their native geographical range and more mesic parts of Australia. Our results demonstrate that cane toads phase shift a key behaviour to survive in a harsh semi-arid landscape. Behavioural phase shifts have rarely been reported in invasive species but could facilitate ongoing invasion success.

Keywords: Rhinella marina; cane toad; invasive species; plasticity; temporal niche shift.

Figure 1.

(a) Study site with a bore-filled reservoir in the foreground. (b) An adult cane toad fitted with an acoustic tag.

Figure 2.

Hour of day during which cane toads (n = 20) entered the water during the (a) early dry season and (b) late dry season (n = 6). Graphs show means and standard errors. Solid line shows mean air temperature, whereas dotted lines show sunrise and sunset. The mean number of visits made to water by cane toads is plotted against (c) the mean number of hours they spent immersed in water and (d) the mean number of hours they spent on land during the early dry season. (Online version in colour.)