Mountain Lions' Impact on a Small Ecosystem
Student Summary by Elizabeth Li
Original Source: Stanford University, ScienceDaily, June 27, 2026
Background: When wolves returned to Yellowstone Park, effects of their presence rippled throughout the entire food chain. The predators drove elk (i.e. large deer species) away from their over-grazed feeding grounds, allowing plants to regenerate and riverbanks to stabilize, changing the structure of the ecosystem itself. This series of effects is called a trophic cascade, and is usually observed in large regions. When the chain involves a producer (plants), a primary consumer (herbivore/prey), and a secondary consumer (predator/carnivore), it is referred to as a tri-trophic cascade.
Objective: Researchers at Stanford saw an increase in mountain lion activity at the Jasper Ridge Biological Preserve, about 45 miles south of San Francisco, between 2015 and 2020. They wanted to find out the exact changes that the mountain lions had on the ecosystem and how these effects translated through the entire preserve.
Method: Using vegetation surveys and motion-activated cameras, scientists observed how the system was affected as mountain lion activity increased.
Results: Two different trophic cascades were discovered. One involved the mountain lions, deer, and plant life, a tri-trophic cascade. The other involved smaller predators that coexisted with the mountain lions. Lesser predators such as the coyote and bobcat were observed less frequently in the area, likely to avoid the larger and more dominant newcomers. Foxes appeared to benefit from the reduced coyote and bobcat activity, and their increase may in turn have led to fewer sightings of rabbits, one of their primary prey species. Furthermore, similar to the Yellowstone situation, deer activity declined and woody plants, including young oaks, showed signs of recovery. This kind of predator-driven change is also known as the ecology of fear, where the presence of a predator can influence where animals travel and forage, even without direct predation. The evidence for the deer, coyote, and bobcat changes was strong, but the researchers note that the effects on vegetation, foxes, and rabbits remain tentative and could also reflect environmental factors such as shifting fog patterns or temperature.
Conclusion: Although scientists do not yet know why mountain lions began to visit, their impact highlights the biological importance of an apex predator in a balanced food chain. Moreover, as more of the world becomes urbanized, small preserves with their own unique ecosystems become increasingly important to support the biological diversity of the planet.
