What do we lose as large carnivores disappear?

Top predators - gone
A world without top predators? Wolves, for example….Credit: Doug McLaughlin, Oregon State University

Globally, we are losing our large carnivores. That is the central conclusion of a large international study (participants from the U.S., Sweden, Australia, and Italy). These are the animals at the top of the food chain, the ones people most readily recognize. There aren’t many species; scientists identify just 31 significant species such as bear, wolf, lion, leopard, tiger, otter, cougar and lynx. Of these species, 17 now occupy half (or less) of the former ranges and 75 percent of them are declining in population. Some species are already exterminated (Lobo wolf, for example) or driven completely out of large natural ranges (such as the Eastern U.S.). The big question addressed by the study, published in Science [10 January 2014, paywalled, Status and Ecological Effects of the World’s Largest Carnivores] is what does the decline of large predators mean for the environment?

The problem, both historically and currently, is that top predators nearly always compete with human beings for prey animals. They take deer, elk, reindeer and many other species that humans hunt for recreation or food. They also kill domesticated animals. Either way, the tendency has been to eradicate the predators or at a minimum drive them out of human inhabited land. Humans tend to be quite pleased with the results – more game animals, no loss of livestock. However, removing top predators changes the ecosystem.

Unfortunately, the ecological effects are often initially less dramatic. In fact, the phrase used by ecologists suggests just how ‘technical’ the results can be – they call it a trophic cascade. The effects spread throughout the ecosystem. Remove a top predator, say the wolf from the Yellowstone region of the U.S., and over a few decades the population of elk, the wolf’s natural prey, overpopulates. The overpopulation results in overgrazing, which reduces food for many other species including rodents and birds. Eventually, the entire ecosystem is affected.

This is not easy to document. One of recommendations of the study is that more predator-ecosystem research is needed. Only about 7 of the major predators are well-studied. In particular, the long-term effects of a predator-less environment need to be examined. The scientists want to build a case for the preservation of predators and a restoration of the natural range and role in the environment. This is hard to argue if they can’t provide evidence of the harm done by removing all large predators.

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