Pumas’ fear of humans precipitates changes in plant architecture

Abstract

Fear of predation can elicit strong behavioral responses from prey, with impacts that cascade through food chains. While this indirect effect of natural predators on ecosystems is becoming better understood, far less is known about how humans—the world’s most ubiquitous super-predator—influence subsequent trophic levels through changes in carnivore habitat use and behavior. Here, we combined puma GPS tracking data with field experiments to understand the extent to which anthropogenic development has cascading impacts from pumas to plants. We examined spatial patterns in puma feeding sites and found that pumas preferentially kill deer away (>340 m) from human development. This aversion appears to create refugia for deer, as deer more than doubled their relative activity near (<70 m) human development. In addition, deer more than quadrupled their consumption of woody vegetation at low-risk sites close to humans relative to comparable high-risk sites far from humans and consumed a greater percent of the forage available in sites near humans than in comparable sites farther away. Increased browsing by deer in near human, or low-risk, sites induced woody plants to become bushier (by removing apical dominance) than those away from humans, or high-risk sites. The cascading interactions from pumas avoiding people to changes in plant architecture appear to have increased available food to deer (i.e., bushier plants have more available branch ends providing potential bites of food than less bushy individuals) and may have other, as yet undocumented, ecological effects.