Reviving ecological functioning through dingo restoration.

Abstract

Invasive species are regarded as one of the top five leading causes of the global extinction crisis. The majority of threatened species recovery plans therefore call for lethal control of invasive species, particularly predators. Vast resources are expended to combat the threats posed by invasives, and considerable research efforts have been devoted to developing best practice pest control practices; with little success overall. The reason for this may be that although invasive species cause extinctions, they are not the ultimate cause. Instead, the shift to invasive-dominated states is driven by an underlying loss or lack of ecological resilience. One of the leading processes that might result in widespread resilience loss, and release of invasive species, is the control or absence of apex predators. Across the globe, and in every habitat investigated, apex predators play a keystone role in enhancing ecological resilience to the damaging influence of environmental perturbations. I tested the hypothesis that state shifts to invasive dominance are symptomatic of the disruption of top-down regulation, and that ecological resilience is largely determined by the social stability of apex predators. Australia presents a unique opportunity to examine these ideas because it is here that mammalian invasions and extinctions have been most severe; pest control is intensive and widespread; and only a single large mammalian predator, the dingo (Canis lupus dingo), is extant. I studied the interactions between dingoes, invasive mesopredators, herbivores, small mammals and vegetation in a series of sites across the arid zone, representing different levels of predator control (poison-baiting). Four of the sites were monitored over 2-3 years to study the effects of predator control cessation and intensification. This study was therefore conducted on both a spatial and temporal scale, providing not only correlative, but also (quasi) experimental evidence from large-scale predator manipulations. The results of this study indicate that ecosystem state shifts to invasive-dominated and degraded landscapes are a consequence of predator control. Where threatened species survive, dingoes were consistently found besides them. Where dingo populations were allowed to recover, invasive and opportunistic species declined considerably, and native biodiversity and productivity increased. The ecological benefits of dingoes were more pronounced and consistent when their social stability was considered. The positive influence of dingoes, and the negative effect of predator control, even outweighed the influence of rainfall in the desert. Whether conducted in the name of the pastoral industry or biodiversity conservation, predator control benefitted neither and undermined both. The results of this study suggest that relaxing human intervention, and allowing large predators to re-assume their natural roles, can rapidly restore ecological resilience and reduce the threat of invasive species. I offer an alternative model for ecological restoration, in which the promotion of predators forms the foundation for recovery programs of threatened species.