Using a natural population collapse of an invasive species to assess the benefits of invader control for native species

Efforts to control invasive species often assume that suppressing invader abundance will benefit impacted native species, but that assumption may sometimes be in error. In some systems, reducing invader abundance may have little effect. At our study site in tropical Australia, numbers of invasive cane toads (Rhinella marina) declined 98% over a 27-month period post-invasion, but none of the 19 native species we monitored increased in counts during that period. Because cane toads impact native fauna primarily via rapid extirpation of top-predators, subsequent reduction in invader abundance may confer little immediate benefit. Short-term culling of cane toads in already-colonised areas is likely to be less beneficial to native species than preventing the spread of cane toads to new areas, or buffering the initial impact of toad arrival through Conditioned Taste Aversion training of vulnerable taxa. More generally, exploiting natural declines in invader populations as a proxy for eradication measures provides a low-cost opportunity to assess the potential for native fauna to passively recover over the short-term. Monitoring native fauna during periods of invader decline can tell us whether or not invader control is likely to confer short-term benefits for native fauna.