In a world where ecosystems are delicately balanced, the absence of certain species can have profound effects. Imagine a vibrant forest, a haven for diverse life forms, from birds to salamanders, and once upon a time, wolves. These wolves played a crucial role in maintaining the forest's health, but their disappearance has left a void.
Human activities, such as habitat destruction, overhunting, and the introduction of new species, have led to the extinction of some creatures and the adaptation and spread of others. As an ecologist, I'm intrigued by how these changes impact our ecosystems and whether the new arrivals can step into the roles of the missing species.
Let's focus on eastern North America, where top predators like wolves have vanished, and a new predator, the coyote, has emerged. Wolves once roamed freely across the region, but as human development encroached, they were viewed as threats and systematically eliminated. Today, only a few gray and eastern wolves persist in Canada and around the Great Lakes, with a small population of red wolves in North Carolina.
The disappearance of wolves opened the door for coyotes to expand their range eastward, and they've now colonized most of eastern North America. But are coyotes the new wolves? Can they fulfill the same ecological role?
To answer these questions, I delved into the diets of both species. I reviewed numerous studies on wolf and coyote diets, recording the percentage of scat or stomach samples containing common food items like deer, rabbits, small rodents, and fruit. I compared the diets of northeastern wolves and coyotes, as well as red wolves and southeastern coyotes.
Two significant differences emerged. Firstly, wolves consumed more medium-sized herbivores, particularly beavers in the northeast and nutria in the southeast. These large aquatic rodents have a substantial impact on their ecosystems; beavers alter water flow with their dams, sometimes to the chagrin of landowners, while nutria, being non-native, damage wetlands.
Secondly, wolves have a narrower diet overall. They eat less fruit and fewer omnivores like birds, raccoons, and foxes compared to coyotes. This suggests that coyotes are performing some ecological roles that wolves never did, such as dispersing fruit seeds and controlling smaller predator populations.
But diet alone doesn't tell the whole story. It's often unclear whether coyotes killed or scavenged the deer they ate. So, I also examined studies on ungulate mortality, which tracked the survival of deer and moose and attributed causes of death.
These studies revealed further distinctions between wolves and coyotes. Wolves were responsible for a significant percentage of moose deaths, with 19% of adults and 40% of calves falling victim to them. In contrast, none of the studies documented coyotes killing moose. This indicates that all or nearly all moose in coyote diets are scavenged.
Coyotes are adept predators of deer, however. In the northeast, they killed more white-tailed deer fawns than wolves, with 28% compared to 15%, and a similar percentage of adult deer, 18% compared to 22%. In the southeast, coyotes killed 40% of fawns but only 6% of adults.
The rare killing of adult deer in the southeast could impact other members of the ecological community. When large predators kill adult ungulates, they often leave behind parts of the carcass, providing a crucial food source for scavengers. While there's no data on how often red wolves kill adult deer, it's likely that coyotes don't supply food to scavengers to the same extent.
So, are coyotes the new wolves? The answer is no. While they eat some of the same foods, they cannot fully replace wolves. The differences are particularly pronounced in the northeast, where coyotes rarely kill moose or beavers. Coyotes in the southeast are more similar to red wolves, but they likely kill fewer nutria and adult deer.
The return of wolves could be a natural solution for regions where wildlife managers want to reduce moose, beaver, nutria, or deer populations. However, even with reintroduction efforts, wolves are unlikely to fully reclaim their former range in eastern North America due to the high human population.
Coyotes, on the other hand, thrive around people. So, even if wolves never fully recover, coyotes will at least partially fill the void left by wolves. Humans have altered the world so drastically that returning to pre-human times may be impossible. While some restoration is feasible, researchers must continue to assess the extent to which new species can functionally replace missing ones.
Alex Jensen, a postdoctoral associate in wildlife ecology at North Carolina State University, is the author of this article.
