Predator species are amazing examples of evolutionary success. The way that they interact with each other, with prey animals, and even with Earth’s atmosphere is crucial in keeping our planet and all its varied species living in harmony. You may have heard that brown bears are strong enough to “kill a cow in a single blow,” that a gray wolf eats almost 20 lbs of meat in a single meal, or that leopards have specially adapted shoulder blades that make them excellent climbers. These things are true! However, each of these spectacular traits sometimes puts them into conflict with humans.
For example, sometimes wolves are accused of killing domesticated or livestock animals, and some states allow farmers to kill any wolf they suspect. This article from Oregon State University’s Small Farm program addresses this issue as it applies to coyotes and suggests that killing predatory animals actually exacerbates existing problems with livestock deaths.
Predators have never been so thoroughly studied as they are these days, and it is now well-documented that when humans remove carnivorous species from an ecosystem, it often throws off the natural balance of the area in unexpected and detrimental ways. All major predators play key roles in helping keep the ecosystems they live in – and all the other animals that live there too – healthy and sustainable.
The most obvious role carnivores play in their ecosystem is population control. Gray wolves hunt in packs to take down moose, elk, bison, caribou, and musk oxen, and prey on weak, old, or very young individuals. This ultimately makes the herd stronger and healthier.
In addition, each habitat has what's known as a “carrying capacity,” which is the maximum number of individual animals that the area’s resources can sustain without being significantly depleted or drained. When a population overgrows the carrying capacity of the area it inhabits, the animals living there can no longer find enough food or shelter and begin to die off. The presence of predators helps keep prey animal populations below carrying capacity, which in turn keeps food sources from being damaged by overgrazing.
When sea otter populations declined due to the fur trade, the populations of their favorite food - sea urchins - boomed, and as a result the sea urchin’s favorite food - kelp forests - shrank drastically. As otter populations rebounded due to conservation efforts, they feasted on the omnipresent urchins, and the kelp forests grew back again!
Without the presence of wolves, the deer in Yellowstone National Park ate everything they could, turning forests into grasslands and changing the species distributions of the area as the animals followed the edge of the receding forests. When the wolves were reintroduced, the trees grew back again, and the animals that relied on them returned as well. These aren’t isolated cases; there are so many similar stories that it’s easy to see how important carnivores are in maintaining the ecosystems around them.
Predatory animals also help slow the effects of climate change! By keeping herbivore populations in check, carnivores can also help with what is called “carbon sequestration.” Plants store carbon dioxide from the atmosphere in their leaves, stems, and the soil around their roots, which means there is less of it in the atmosphere contributing to climate disturbances. When plants die, some of that carbon stays in the soil, but if the soil is disturbed, it will be released back into the atmosphere. Healthy forests with reduced soil erosion and continued promotion of carbon sequestration in the ground help keep excess carbon dioxide out of the atmosphere, and top carnivores like gray wolves appear to play an indirect role in this process.
Some animals that people think of as “top carnivores,” like bears, are actually dietary omnivores: they eat grasses, roots and bulbs, fruits and berries, nuts, and tubers. The herbivorous components of their diets are just as crucial to the ecosystems they live in as their predatory behavior. The seeds of many plants won’t germinate – develop – unless they’ve gone through the digestive tract of an animal first. Bears maintain large territories that they travel across frequently, and they excrete the seeds of the plants they eat as they go, functioning as an important mechanism of seed dispersal.
In all, carnivores play a number of very important roles in the ecosystems they live in - sometimes in obvious ways, but often in indirect ones as well. As we continue to balance human needs with the existence of wild animals – not to mention conservation and reintroduction programs - we will continue to learn about the roles they play within their habitats, and how important they are to keeping the natural world around us healthy.