Urban expansion drives niche expansion of a top carnivore (Puma concolor)
Land use change and direct persecution have been the main drivers behind the loss of large carnivores globally. However, there is growing recognition that large carnivores are more adaptable to land use change than previously thought. One mechanism by which these species adapt to developed landscapes is through behavioral plasticity, especially modification of foraging behavior. Foraging plasticity has been implicated as a major determinant of species’ success in developed landscapes, and could also be important for large carnivores, who rely on spatially heterogeneous prey species. We examined the foraging strategies of a large carnivore, the cougar (Puma concolor), and the consequent implications for their persistence in human-modified landscapes. Through the analysis of stable isotopes, we compared the niche of three cougar populations in Colorado: (1) a contemporary wildland population (2) a contemporary near-urban population (3) a historic near-urban population from the 1980s. We also examined how foraging strategy might impact risk of mortality, using mortality data from GPS-collared individuals to construct hazards models. Finally, we investigated how demographic class and individual space use (i.e. housing density at GPS locations) contributed to intra-population variability in diet, using linear models to predict isotopic signature.
Our spatio-temporal niche analysis revealed that resource use by cougars is quite variable. Contemporary cougars in near-urban ecosystems (n = 41) relied significantly less upon native herbivores (63-79% of diet) than those in wildland ecosystems (n = 58; 91-99%). However, 30 years ago, cougars in the near-urban ecosystem were more reliant on native herbivores (n = 7; 72-96%). The contemporary near-urban cougar population occupied a dietary niche 1.5 x broader than the wildland cougar population (p = 0.01). This intra-population variation in diet was primarily driven by age-sex class and space use. Individuals that foraged in the most urban habitat utilized a higher diversity of prey, obtaining 20% more of their diet from synanthropic wildlife and domestic animals. However, this “urban opportunist” foraging strategy was ultimately maladaptive, resulting in higher rates of mortality for individuals that utilized urban areas. For every 10% increase in housing density at an individual’s GPS locations, hazard risk increased by 6.5%. Our study highlights the extreme plasticity of a large carnivore, and demonstrates that the niche of important ecosystem regulators is not constant over space or time, but appears to be expanding with human development--with potential costs for population persistence.