A new study out of Australia, published in Ecology Letters, found that restoration of top predators such as the dingo may be a more effective method to limit the impacts of invasive species (in this case, introduced mesopredators such as foxes and cats) than direct control of invasives. The authors found that rather than controlling invasives, pest control inadvertently promoted invasive and opportunistic species by disrupting dingo populations. Increases in populations of invasive species were, according to this study, more of a symptom of the ‘ecological meltdown’ caused by predator extirpation rather than a direct cause of biodiversity loss. The study found that dingo social stability, rather than dingo abundance, was the best predictor of these top-down effects. These findings provide an interesting parallel to recent studies of wolf populations that suggest the importance of predator social structure in addition to density.
It will be interesting to see whether this type of ecological cascade is generalizable to other regions where invasive species may not be primarily mesopredators. Several previous studies have found evidence supporting or contesting the hypothesis that the reintroduction of wolves into Yellowstone National Park has led to a behaviorally-mediated trophic cascade (BMTC), in which aspen suffer less browsing in areas where elk are at higher risk of wolf predation. In a new paper in Ecology, Kauffmann and colleagues report on a study using data from tree demography studies and experimental exclosures in Yellowstone to test the BMTC hypothesis. Kauffman and colleagues contest the generality of the trophic cascade hypothesis in terrestrial ecosystems, and emphasize the complex nature of how top-down and bottom-up effects interact to structure ecosystems.
Top-down effects on invasive species: Figure from Wallach et al. 2010