Urban areas are projected to expand exponentially through the first third of the 21st century, which creates a pressing need to understand the complex interactions within urban ecosystems. Vertebrate scavengers are particularly suited for urban studies as human activities effect food availability in multifaceted ways (e.g. landfills provide consistent food; harvesting prey species can decreases food availability). Carcass removal by scavengers stabilizes food webs by increasing connectivity and is an essential ecosystem service, which reduces the spread of disease, increases nutrient distribution, and controls pest species. Ecosystem stability may be undermined if vertebrate scavengers rely on anthropogenic foods overmuch. Therefore, the response of the scavenger community to urbanization is critical for future ecosystem stability. To investigate these effects, we placed 110 camera traps along a 400-mile urbanization gradient in New York during the summer of 2017. We then compared the scavenger community composition (i.e. species richness, percent occurrence, nestedness) and scavenger efficiency (i.e. carcass detection time, removal rates) between urbanization levels. We predicted that small mammals (e.g. raccoons, small rodents) would thrive in urban areas. Additionally, obligate scavengers and larger carnivores will provide the bulk of carcass removal in natural areas and species richness and carcass detection time would co-vary.
Results/Conclusions
Scavenger community composition varied significantly with urbanization (ß=1.26, p =0.000). We observed fifteen scavengers, with distinct urban specialists. Only raccoons, opossums, and feral cats occurred in urban areas. Raccoons were absent from natural habitats, and bears, coyotes, and turkey vultures were the most frequent. The absence of raccoons indicates a top down mediation by these larger scavengers. Species richness was highest in suburban areas, suggesting a higher niche diversity (SRnatural=6, SRsuburban= 14, SRurban=3). Finally, the community was highly nestedness (Z-NODF=3.0539, p=0.01), creating the potential for interspecific interactions. Scavenger efficiency results were mixed. Removal rates did not differ significantly, but different species performed carcass removal in each habitat (χ2=74.08, p=0.0005). Coyotes and turkey vultures consumed more carcasses in natural habitats (M=303.95, SD=1114.95; M=94.43, SD=298.02), while foxes and turkey vultures did so in suburban areas (M=197.88, SD=352.45, M=53.12, SD=107.80). Raccoons dominated carcass removal in urban locations (M=7434.33, SD=62373.47). Urban habitats had the shortest carcass detection times and natural areas the slowest (F(2, 86)=23.15, p<0.00001). In conclusion, urbanization has a clear impact on the scavenger community structure. Likely, the redundancy within the scavenger community and increased scavenging by smaller animals compensated for the lack of larger carnivores and obligate scavengers in urban habitats.