Experimental evidence for density-dependent responses to mortality of snake-necked turtles

Abstract

Density-dependent compensation has rarely been demonstrated in long-lived vertebrates in highly variable environments, such as the wet-dry tropics, where complex factors impact on vital rates. We used an experimental manipulation of population density in six replicated wild populations of the northern snake-necked turtle (Chelodina rugosa). We show that this species can rebound rapidly following reductions in density, and so is resilient to harvest and predation by pigs. Remarkably, in some populations, turtle abundance took as little as 1 year to recover from a strong negative perturbation (>50% experimental population reduction) in adult density. This was achieved through an increase in hatchling recruitment and survival into larger size classes. Our manipulative experiments, viewed concomitantly with previous experimental and correlative research, challenge the general perceptions that freshwater turtles universally are highly susceptible to any form of off-take and that high sub-adult and adult survival is crucial for achieving long-term population stability in freshwater turtles generally. In the case of C. rugosa, such generalities would produce overly cautious prescriptions for sustainable management.