A new study has recently established that a number of factors contribute towards the development of “global hotspots” of declining carnivore populations. With losses associated with a number of large predators – including bears, dingoes, lions, otters and wolves – these changes are conjectured to be responsible for adverse changes in a variety of diverse landscapes, ranging from the tropics to the Arctic.
A Global Carnivore Loss
The authors of the latest study – which appears in the latest issue of the journal Science – indicate a decline in 75 percent of all the 31 large-carnivore species. In addition, 17 of these species now inhabit much smaller regions – less than half of their former ranges.
A decline in multiple carnivorous species has been observed in the Amazon, southeast Asia and southern and East Africa. As was to be expected, the hardest hit regions span across the developed world, where many large carnivores have been eradicated; this includes areas throughout the United States and Western Europe.
Professor William Ripple, lead author of the latest paper, worked as part of an international team of researchers, with many of his colleagues hailing from the U.S., Australia, Italy and Sweden. Based in the Department of Forest Ecosystems and Society at Oregon State University, Ripple reiterated the finding of widespread decline in species of large carnivores, before going on to describe the collapse in the creatures’ ranges:
“Globally, we are losing our large carnivores… Their ranges are collapsing. Many of these animals are at risk of extinction, either locally or globally. And, ironically, they are vanishing just as we are learning about their important ecological effects.”
Trophic Cascades Affect Entire Ecosystems
The research team performed a systematic review of pre-existing scientific reports. They identified a total of seven different species of large carnivores that had been extensively studied for their systemic impact on various ecological systems – phenomena defined as “trophic cascades.” The seven species comprised of cougars, dingoes, leopards, African lions, Eurasian Lynx, sea otters and gray wolves.
Ripple, along with co-author Robert Beschta, previously documented a trophic cascade when studying the influence of scant populations of cougars and wolves in North American national parks, including Yellowstone. They confirmed that fewer predators culminated in a boom in populations of browsing animals, including deer and elk. In turn, this increased browsing affected the forest stands and riparian vegetation – situated at the interface between land and rivers – and displaced birds and small mammals.
Meanwhile, in parts of Africa, declining lion and leopard populations have been attributed to a attendant increase in olive baboons (a.k.a Anubis baboons), which are found in 25 countries throughout the continent. Olive baboons are omnivorous creatures, seeking out nutrition from a wide range of environments and eating virtually all types of plants, invertebrates and small mammals; as a result, the baboons have wreaked havoc on crops and livestock.
Killer whale populations have also been linked to sea otter numbers, particularly in western Alaska. In the last 10 years, the sea otter population has plummeted considerably – a trend that many scientists have correlated to increased predation from killer whales. In 2003, Dr. Alan Springer and colleagues published a study in the Proceedings of the National Academy of Sciences, entitled Sequential megafaunal collapse in the North Pacific Ocean: An ongoing legacy of industrial whaling? The group found, prior to the late 1970’s, almost all species of great whale in the North Pacific were hunted to near-extinction. Since these whale species were prime food sources for killer whales, they were forced to find alternative nourishment, in the form of smaller marine mammals. As a consequence, the killer whale began hunting and consuming seals. This caused a change reaction, however, which led to an increase in sea urchins and a knock-on loss of kelp beds, as sea otters were no longer present to keep the sea urchins in check.
In interpreting all the research, Ripple and colleagues call for further research to gain deeper insight into the relationship between large carnivores and their ecosystems. The team argues against previous misconceptions that suggested predators are harmful to their environments and merely destroy wildlife, proclaiming these concepts to be outdated. Instead, they explain that carnivores play highly complex roles in their ecosystems and yield “social and economic benefits.”
Ripple refers to the esteemed American ecologist Aldo Leopold in making his point. Leopold was instrumental in furthering wildlife conservation efforts, and appreciated the intricate relationships between predators and their ecosystems.
“Human tolerance of these species is a major issue for conservation. We say these animals have an intrinsic right to exist, but they are also providing economic and ecological services that people value.”
Ripple also points out how quickly restoration of large carnivores can affect a beleaguered ecosystem, referring to the radical change observed in Yellowstone and Finland, upon the return of wolves and Eurasian lynx, respectively. However, Ripple posits that full ecosystem restitution may not be possible in those regions where a decline in vegetation has led to soil erosion.
Nonetheless, after studying the widespread impact that carnivore loss has on ecosystems, worldwide, the researchers call for international initiatives to conserve large predators.
By James Fenner