Put down that camera—ecotourism could be making wildlife less wild.

Protected areas receive more than 8 billion visitors per year, and wildlife tourism grew 30 percent between 1998 and 2008. Now a new study has found that all that interaction between humans and wildlife poses dangers for animals.

“We know, for example, that when you put a hiking trail in an area, you start losing wildlife—but we didn’t know how and why that happens,” said Dan Blumstein, a behavioral and conservation biologist at the University of California, Los Angeles, and coauthor of the study, which was published Friday in the journal Trends in Ecology and Evolution. “Animals are pretty smart in terms of their anti-predator behavior, but we were able to come up with a framework linking domestication with what happens during tourists visits to a natural area.”

In some cases, guides will explicitly habituate animals so that visitors can get closer to them, as happens in parks in Uganda where tourists come to watch chimpanzees.

The presence of people also pushes out predators. This so-called human shield protects wildlife from their normal predators but leaves them less vigilant about defending themselves.

Researchers, for instance, watched the distance at which the animals would start to flee in the face of danger. Rural squirrels fled at almost seven times the distance of urban squirrels.

Another study found that urban birds species wriggled, pecked, and bit less than rural individuals when removed from mist nets, suggesting city birds exhibit more relaxed behavior than their country counterparts.

RELATED: Save a Fearsome Predator by Swimming With It

Fish behave differently around people as well. Blumstein has been part of studies where researchers swam around fish with and without spear guns in different marine environments.

“They know spear guns in the marine protected area, but they respond differently in the protected areas to people than they do off the protected areas,” he said. Because fish feel safer in protected areas, it could lead to fish being illegally fished more easily.

When people constantly go to protected areas, they might be keeping predators away permanently, but if humans are only present a few months a year or a few hours a day, the animals may become more vulnerable to predation or poaching. Blumstein said the goal of the study was to set up a framework for future lines of research.

“We want to lead to a better understanding of the true peril that our loving nature may have on the wildlife that we go to look at,” he said.

One potential solution is to close off some wild areas to tourism.

“In fragmented populations, where animals have problems moving around, just a few mortality events can move a stable population to a place where it’s unstable,” Blumstein said. “Eight billion people visiting natural areas can’t but have an impact, and we’re focusing on one very plausible impact.”