About 45 miles south of San Francisco sits Jasper Ridge Biological Preserve, a small, mostly unremarkable piece of land. It is tiny by conservation standards, around 480 acres in size. According to a new Stanford-led study, this small preserve has proven something significant about how ecosystems actually work.

Mountain lions started appearing more frequently on trail cameras at Jasper Ridge beginning in 2015. Researchers spent the following years tracking them, using motion-activated cameras and vegetation surveys. What they found was a clear example of what ecologists call a trophic cascade, playing out in a space barely larger than a few city blocks. A trophic cascade is an ecological chain reaction that occurs when a change in one part of a food web — usually involving a top predator — triggers indirect effects that ripple down through multiple levels of the ecosystem.

Lions Caused Plants to Recover

As mountain lion activity increased, deer activity decreased, and plant life began to recover. This makes sense, since mountain lions hunt deer. When the lions returned, the deer became more cautious and spent less time out in the open. With fewer deer consistently browsing and trampling the landscape, young plants finally had room to grow. Oak seedlings and other woody plants that deer typically eat began thriving again.

The researchers found something unexpected in the process. The lions did not need to catch many animals to change the entire preserve. The mere smell or sound of a mountain lion nearby was enough to make other animals shift their daily habits. Scientists call this phenomenon the ecology of fear.

A Ripple Effect 

The lions’ presence rippled beyond plant life. As puma activity increased, coyote and bobcat activity dropped. Researchers believe these mid-sized predators were likely avoiding the area or shifting their schedules to steer clear of the larger predator. With fewer coyotes and bobcats wandering, foxes seized the opening and began appearing more often. This shift may have, in turn, put pressure on rabbits, one of the foxes’ primary prey.

This effect shows how one apex predator wandering through the preserve can change the behavior of an entire food chain. Researchers had originally assumed this kind of cascade was unlikely in small, suburban-adjacent preserves, but this study shows that it can happen.

A Tiny Preserve, A Bigger Conclusion

The real benefit of this study is how to apply it on a wider scale. In the United States, 82% of protected areas are under five square kilometers. According to Rodolfo Dirzo, the study’s co-author and a Stanford biology professor, this means spaces like Jasper Ridge will likely matter more as cities continue to expand.

“Maintaining sites where there is an entire community of animals, from predators to prey to the prey’s resource base, is very important,” Dirzo said. “When one piece is missing — and it’s typically the top predators that require larger areas and are more sensitive to human impact — we will no longer have fully functioning ecosystems.”

Even Small Preservation Matters

Most conversations about conservation default to picturing vast, untouched wilderness, such as national parks and remote reserves far from any human footprint. This study offers a reminder that smaller patches of habitat can support fully functioning ecosystems, as long as they remain connected to larger wild areas.

As cities continue to grow and open space continues to shrink, the lesson from Jasper Ridge is simple. Protecting what remains, even a few square kilometers tucked next to the suburbs, still matters.