Abstract
Humans have outsized effects on ecosystems, in part by initiating trophic cascades that impact all levels of the food chain.1,2 Theory suggests that disease outbreaks can reverse these impacts by modifying human behavior,3,4 but this has not yet been tested. The COVID-19 pandemic provided a natural experiment to test whether a virus could subordinate humans to an intermediate link in the trophic chain, releasing a top carnivore from a landscape of fear. Shelter-in-place orders in the Bay Area of California led to a 50% decline in human mobility, which resulted in a relaxation of mountain lion aversion to urban areas. Rapid changes in human mobility thus appear to act quickly on food web functions, suggesting an important pathway by which emerging infectious diseases will impact not only human health but ecosystems as well.
Highlights
In the Santa Cruz Mountains of California, two distinct types of human development impact large carnivores: urban boundaries where dense residential development meets wildlands and lower density exurban and rural residential development where houses and wildland vegetation intermingle
Humans present a substantial source of mortality for many taxa and are especially deadly to large carnivores, killing adults at rates 9 times higher than any of their other predators.[5]
While there have been many examples of trophic cascades where humans occupy the top level in the food chain, it is unknown whether humans can be subordinated to intermediate links in trophic cascades by other lifeforms, reversing the sequence of positive and negative effects on ecosystem functions
Summary
In the Santa Cruz Mountains of California, two distinct types of human development impact large carnivores: urban boundaries where dense residential development meets wildlands and lower density exurban and rural residential development where houses and wildland vegetation intermingle. Mountain lions (Puma concolor) are the largest carnivore in this system and the majority of their mortality is caused by humans (Table S1). Human threat creates a landscape of fear whereby mountain lions generally avoid human voices[9,10,11] and habitat close to human infrastructure,[12] resulting in increased energy expenditure by mountain lions,[13] reduced vagility, and smaller home ranges.[14] This landscape of fear has cascading impacts on mountain lion kill rates of deer,[15] plant architecture,[16] and rodent space use.[1]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
