Global and local decline of large animals at the top of the food chain, so-called “apex consumers”, has caused disruption of ecosystems. This is shown in a study which is recently published in Science. The large animals, which not necessarily have to be predators, consume prey or vegetation at top levels of the food chain and are essential for stable ecosystems. The authors argue that the loss of the top consumers is the most pervasive influence of Man on Mother Nature.
Some examples of these disruptions which are decribed in the publication are the following:
The extirpation of wolves in Yellowstone National Park led to over-browsing of aspen and willows by elk, and restoration of wolves has allowed the vegetation to recover.
The reduction of lions and leopards in parts of Africa has led to population outbreaks and changes in behavior of olive baboons, increasing their contact with people and causing higher rates of intestinal parasites in both people and baboons.
Dramatic changes in coastal ecosystems have followed the collapse and recovery of sea otter populations; sea otters maintain coastal kelp forests by controlling populations of kelp-grazing sea urchins.
Large animals, once found all over the world, have been important representatives of fauna that shaped ecosystems structure and dynamics. Hunting and habitat fragmentation by humans who think they must exploit nature, caused population decline not only of large predators, such as wolves, lions, whales and sharks, but of large herbivores, such as bison and elephant, too. This decline has had far-reaching and often surprising consequences, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality, carbon sequestration and nutrient cycles.
The loss of large animals from an ecosystem triggers a chain of effects moving down through lower levels of the food chain. These ecological phenomena, though complicated and therefore not easy to recognise, are fundamentally important.
The group of international scientists led by James Estes from Santa Cruz University of California, could not perform experiments to prove their theory. They had to review many long-term records and observations of natural changes over a long period to identify the interactions they describe in their publication. Or as Estes put it: “With these large animals, it’s impossible to do the kinds of experiments that would be needed to show their effects.”
The study’s findings have profound implications for conservation. “To the extent that conservation aims toward restoring functional ecosystems, the re-establishment of large animals and their ecological effects is fundamental,” Estes said. “This has huge implications for the scale at which conservation can be done. You can’t restore large apex consumers on an acre of land. These animals roam over large areas, so it’s going to require large-scale approaches.”