Mountain lions reshape wildlife activity in a small California preserve

Mountain lions that began visiting a small preserve near Silicon Valley more often altered the behavior of several other species, according to a Stanford University-led study. The findings suggest small protected areas can support ecological effects usually associated with large wild areas when they remain connected to broader habitat.

The research, published in Ecology and Evolution, examined Stanford’s Jasper Ridge Biological Preserve, also known as ’Ootchamin ’Ooyakma, about 45 miles south of San Francisco. Stanford said motion-triggered cameras recorded rising mountain lion activity there from 2015 to 2020.

Researchers reported that deer activity fell during the period of more frequent puma visits compared with earlier years when mountain lions were rare or absent from the preserve. Vegetation surveys also found that woody plants favored or damaged by deer, including young oaks, were doing better.

Scientists describe these chain reactions as trophic cascades: changes at the top of a food web that ripple through other species. Stanford said such effects have been studied most often in large protected areas, including work on wolves in Yellowstone National Park, but the Jasper Ridge study indicates they can also occur in smaller suburban preserves.

Predator presence changed more than deer behavior

The Stanford team found evidence for two linked patterns. One connected mountain lions, deer and vegetation. Another involved mid-sized predators: as puma activity increased, coyotes and bobcats were recorded less often, according to the study.

The researchers said coyotes and bobcats may have avoided the area or shifted when they were active to reduce encounters with the larger cats. With those animals less visible in the data, foxes appeared more frequently, and rabbit activity may have declined as a result.

The study frames these changes through what ecologists call the “ecology of fear,” in which animals respond not only to being hunted but also to the risk of encountering a predator. Stanford said the lower-level findings involving plants, foxes and rabbits remain provisional because other factors, including fog and temperature changes, could also have influenced the results.

The effects on deer, coyotes and bobcats were clearer, according to the researchers. Rodolfo Dirzo, a Stanford biology professor and study co-author, said small protected sites matter because many U.S. protected areas are small; Stanford cited a figure of 82% under 5 square kilometers, or about 2 square miles.

Why pumas used the preserve remains unclear

Researchers do not know why mountain lions increased their visits to Jasper Ridge. Stanford said one possibility is that female pumas used the preserve as a safer place to raise young, noting that a female with kittens appeared on camera during the study period.

The preserve is too small to sustain its own resident puma population. Stanford said mountain lions in the Santa Cruz Mountains range across about 20 to 170 square kilometers, or roughly 8 to 66 square miles, so the animals recorded at Jasper Ridge were visitors.

Elizabeth Hadly, the study’s senior author and a Stanford professor emerita of biology, said mountain lions generally avoid people despite occasional sightings in San Francisco or nearby suburbs. Stanford said they are also nocturnal, reducing the chance of encounters during periods when people are active.

Hadly noted that humans are the leading cause of mountain lion deaths through hunting and vehicle collisions. The study’s authors said keeping small preserves connected to larger wild areas can help maintain full animal communities, from top predators to prey and the plants those prey species use.

This story draws on original reporting from Phys.org.