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In parts of Australia, people drop poisoned meat from airplanes or helicopters or leave it along dirt roads to keep dingo numbers under control. The justification is that dingoes attack livestock and need to be suppressed. But dingo poisoning has set off a cascade of ecosystem changes that affect other wildlife: according to a new study, small mammals are taking a hit too.
Figuring out what happens when you get rid of top predators is tough. It’s impractical to do a large-scale experiment in which predators are removed from an ecosystem, and such studies would often be illegal or ethically questionable anyway.
But the study authors had the chance to follow a “natural experiment”. In New South Wales, Australia, they identified seven pairs of sites with different levels of dingo control. Within each pair, dingoes had been regularly poisoned at one site for the last five years; at the other site, less than 50 kilometers away, people hadn’t made much of an effort to control dingoes.
The researchers monitored kangaroos, wallabies, foxes, cats, possums, and small mammals such as rodents at each site. They searched for the animals by identifying footprints, scanning the area while driving, or setting traps with peanut butter, oats, and honey.
At the sites with frequent poisoning, the authors found more kangaroos and wallabies and more signs of fox activity, presumably because fewer dingoes were hunting or harassing those animals. Since kangaroos and wallabies are herbivores, the density of understory plants went down. And the number of small mammals, which take cover among plants and are preyed on by foxes, also dropped.
“Dingo control programmes in conservation reserves may be counter-productive from a biodiversity conservation perspective,” the authors write in Proceedings of the Royal Society B. Managers will need to find a way to keep dingo numbers up and farm animals safe at the same time. — Roberta Kwok | 13 March 2014
Colman, N.J. et al. 2014. Lethal control of an apex predator has unintended cascading effects on forest mammal assemblages. Proceedings of the Royal Society B doi: 10.1098/rspb.2013.3094