Mountain Lion Visits Trigger Trophic Cascade in a Small California Preserve

Camera traps from 2015-2023 at Jasper Ridge Biological Preserve (4.9 km² of oak woodland and grassland near Stanford) recorded a marked rise in Puma concolor activity. Deer detections fell 34 %, nighttime coyotes declined 25 %, and gray fox sightings rose. Vegetation surveys in 2006, 2015 and 2023 showed a 64-fold increase in woody plant cover, including native oaks and sagebrush. The pattern matches a trophic cascade driven by predator-induced “ecology of fear.”

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Trophic cascades are illustrated by wolf reintroduction in Yellowstone, where apex predators altered elk behavior and riparian vegetation. Jasper Ridge, a 4.9-km² peri-urban preserve linked to the Santa Cruz Mountains, experienced similar effects through occasional mountain-lion visits.

When mountain lions began appearing more often on trail cameras at a small California nature preserve, coyotes and deer shifted away from nighttime activity, and the woody plants those deer used to ea

Authors link the cascade to behavioral changes: deer avoided lion-marked areas, reducing browsing and allowing plant recovery. Hadly emphasized that humans remain the main cause of mountain-lion deaths, calling humans “the ultimate predator.” Dirzo warned that losing apex predators would degrade ecosystem function, and Sonawane highlighted habitat connectivity between Jasper Ridge and the Santa Cruz Mountains.

When mountain lions began appearing more often on trail cameras at a small California nature preserve, coyotes and deer shifted away from nighttime activity, and the woody plants those deer used to ea

Researchers acknowledge that fog and temperature changes may also affect vegetation, making links to foxes, rabbits and some plants provisional. The reason mountain lions began visiting—perhaps a safe nursery site—remains unknown, and the analysis could not separate behavioral shifts from population changes.

When mountain lions began appearing more often on trail cameras at a small California nature preserve, coyotes and deer shifted away from nighttime activity, and the woody plants those deer used to ea

The study shows that small peri-urban preserves—82 % of U.S. protected areas are under 5 km²—can sustain functional ecosystems when linked to larger wildlands. Wildlife corridors let apex predators shape fragmented landscapes, boosting biodiversity and native plant recovery.

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• “Humans are the ultimate predator on almost every landscape.” — Elizabeth Hadly, Stanford professor emerita of biology

When mountain lions began appearing more often on trail cameras at a small California nature preserve, coyotes and deer shifted away from nighttime activity, and the woody plants those deer used to ea

• “As Sonawane put it: “In the past, small preserves like Jasper Ridge have often been dismissed for holding very little ecological value, but this study shows that when these small preserves are connected to large wilderness like the Santa Cruz Mountains, you can still see magnificent ecological phenomena like trophic cascades.” — Chinmay Sonawane, Stanford Ph.D. candidate

When mountain lions began appearing more often on trail cameras at a small California nature preserve, coyotes and deer shifted away from nighttime activity, and the woody plants those deer used to ea

• “Much like the well-documented cascade triggered by wolves in Yellowstone, we found that increasing mountain lion activity coincided with changes cascading through the food web, from deer and coyotes down to foxes, rabbits, and woody plants,” — Chinmay Sonawane

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• “The trophic cascade documented at Jasper Ridge only works because these cats have a way to get there. It underscores the absolute necessity of preserving wildlife corridors that link urban fringe preserves to larger wild spaces,” — Zara McDonald, president of the Felidae Conservation Fund

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The team will continue camera monitoring and vegetation surveys to clarify drivers of lion visitation and to distinguish behavioral shifts from demographic changes in the food web.

When mountain lions began appearing more often on trail cameras at a small California nature preserve, coyotes and deer shifted away from nighttime activity, and the woody plants those deer used to ea