The removal of wolves and cougars in Pennsylvania long ago is responsible for today’s deer problems — and maybe even the explosion of tick-related Lyme disease, a new study suggests.

These observations come from a Penn State College of Agricultural Sciences-led study of carnivore interactions in 12 countries.

Field cameras were used to study how carnivore communities, from large to smaller predators, affect prey species and even vegetation.

All these elements are related and affect each other, the researchers found.

Though Pennsylvania wasn’t included in the study, its findings hold true for the state, noted David Miller, associate professor of wildlife population ecology at Penn State.

One of the key findings is that when large carnivores disappear, it can devastate the ecology.

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“When you lose a large-bodied species of carnivore, you have other smaller carnivores increase in density, putting pressure on other smaller carnivores, and that can lead to increases in prey species, which might then lead to degradation of plant communities,” Miller said.

“Coyotes and bobcats are preying on different animals than wolves and cougars would,” Miller continued with the Pennsylvania analogy, “and that has implications for how our forests are structured. That fact that we don’t have wolves and cougars means we have more deer, and those deer have overbrowsed the forests.”

Continuing the trickle-down effect, Miller said that the upsurge in coyotes around Pennsylvania — because they don’t tolerate foxes — means there are more mice in our fields and forests.

“That is affecting the prevalence of Lyme disease spread by ticks that spend much of their life on certain mice. So you see, the way these carnivores compete and co-occur has implications for all of our wildlife communities.”

The study, which was published in Ecology Letters, studied carnivores from Botswana to Norway. Carnivores ranged from weasels to polar bears to lions.