The rapid loss of top predators such as dingoes, leopards and lions is causing an environmental threat comparable to climate change, an international group of scientists has warned.
A study by researchers from Australia, the US and Europe found that removing large carnivores, which has happened worldwide in the past 200 years, causes a raft of harmful reactions to cascade through food chains and landscapes.
Small animals are picked off by feral pests, land is denuded of vegetation as herbivore numbers increase and streams and rivers are even diverted as a result of this loss of carnivores, the ecologists found.
“There is now a substantial body of research demonstrating that, alongside climate change, eliminating large carnivores is one of the most significant anthropogenic impacts on nature,” the study states.
The research looked at the ecological impact of the world’s 31 largest mammalian carnivores, with the largest body of information gathered on seven key species – the dingo, grey wolf, lion, leopard, sea otter, lynx and puma.
In Australia the downfall of the dingo, which has been largely pushed out of the country’s eastern and southern states, has had a number of detrimental effects. Dingoes have been culled to prevent them preying on sheep, while inter-breeding with dogs has also had an impact.
Dr Mike Letnic, the report’s co-author and research fellow at the University of NSW, told Guardian Australia that his studies either side of the vast dingo-proof fence showed the consequences of their absence.
“We found there were more small native animals such as poteroos and bilbies where the dingoes were,” he said. “That’s because they [dingoes] suppress foxes, which have given small mammals a really hard time since they were introduced.
“Dingoes also kill kangaroos, so losing them means more kangaroos. That means areas are overgrazed, nutrients are lost from the soil and you risk desertification of areas. More dingoes aren’t ideal for kangaroos, but they are a net benefit to the ecosystem.”
This increase in kangaroo numbers in parts of Australia has had other unintended consequences, with the marsupials targeted by farmers for competing with livestock for prime grazing land. Letnic said they may even be to blame for outbreaks of Ross River fever.
Further afield, researchers found that the reintroduction of wolves to Yellowstone national park in the US caused a reduction in deer numbers, in turn benefiting the park’s trees and plants.
The spread of Lyme disease in the US was partially attributed to booming deer numbers, which host the ticks that carry the disease, while an increase in the number of herbivores grazing is thought to change the flow of local rivers, making them straighter and threatening creatures that dwell in slow-moving waters. Loss of vegetation also removes key carbon storage from the environment.
Letnic said: “A good example is in west Africa, where people removed lions and leopards. They then suffered an outbreak of baboons, which give small animals a hard time but also give people a hard time. They raid crops, which mean that kids don’t go to school because they have to guard the crops all day.
“Overall, we’ve got to find better ways to live with carnivores. They aren’t always easy to live with, but they are an important part of the ecosystem.
“In terms of dingoes, we need to find landscapes where they are left alone or actively promoted. In livestock grazing areas we need to work out what impact they are having and work out a system, perhaps with guard dogs, that we can use to avoid killing them off.”
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