CFAES Give Today

School of Environment and Natural Resources


TWEL William Graser Thesis

The effects of landscape structure on raccoon demographics and disease
William H. Graser, MS
Advisor: Stan Gehrt
Human populations and resultant urbanization have increased globally, often altering the abundance and distribution of wildlife species. Raccoons (Procyon lotor) are a common mesocarnivore, and benefit from urbanization, often attaining their highest densities in urban and suburban areas. Growing evidence suggests that human-induced alterations of the landscape influence the ecology and emergence of wildlife diseases, often with implications for the health and safety of humans and domestic animals. In light of the increasingly close association between wildlife and humans, the need for a better understanding of how human presence and land-use changes affect wildlife populations and wildlife-pathogen dynamics will be vital for the management and conservation of wildlife, and limiting the risk of human exposure to zoonotic diseases.
To better understand how land-use patterns influence raccoon density and demographic patterns, I sampled raccoons at multiple, replicated sites across an urban landscape; the Chicago metropolitan area. I predicted that raccoon density, population structure and demographic patterns (e.g. age structure, sex ratio, reproductive condition, and body condition) would be influenced by land-use. I sampled 18 sites (3 rural open, 8 urban open and 7 urbanized) during April-August, 2005-2006, and captured 530 adult, and 182 juvenile raccoons. Raccoon density varied substantially within land-use types. Additionally, density differed by land-use type (F2,17 = 4.66, P = 0.027); mean density at urbanized sites was lower than urban open, and did not differ from rural open sites. Pooled sex ratios did not differ from 1:1 (M:F) in urban open (P = 0.887) or urbanized (P = 1.00) sites, but did depart from 1:1 (P = 0.001) in rural open sites. There was no association between site type and female reproductive condition (P = 0.959).
There was no association between spring body condition index and site type for males (P = 0.382) or females (P = 0.112). I found no association between summer body condition index and site type for females (P = 0.201), however there was a significant association for males (P = 0.007). The overall age structure of raccoons differed among urban open, rural open, and urbanized sites. The most striking differences were the absence of the oldest age class (V) at urbanized sites and low numbers of age class I individuals at urban open sites.
I found that land-use influences the density of raccoons across this urban landscape, but the abundance of anthropogenic resources and subtle differences in habitat quality may be strongly influencing density at the site level. Furthermore, age structure was influenced by land-use and may have reflected differences in the prevalence and importance of different mortality sources across the landscape.
I tested raccoon sera collected across the Chicago metropolitan area for exposure to Toxoplasma gondii (T. gondii), Leptospira spp., canine distemper virus (CDV), canine parvovirus (CPV), and pseudorabies virus (PRV). My objectives were to: 1) document patterns of exposure to infectious disease agents of public and animal health in raccoons across an urban landscape, 2) test for differences in the patterns of exposure to selected infectious disease agents for raccoons inhabiting different areas of the landscape (i.e. urban open sites, rural open sites, and urbanized areas). Sera were collected from 570 raccoons, 302 from urban open sites, 135 from rural open sites and 133 from urbanized sites. Percentages of seropositive raccoons were 39% for CDV, 51% for CPV, 37% for T. gondii., 33% for Leptospira spp., and 0% for exposure to PRV. I observed a positive correlation between age and seroprevalence for CDV, CPV, T. gondii, and Leptospira spp. Raccoons captured at rural open sites were more likely to be seropositive for CDV than raccoons from urban open sites (adjusted odds ratio {OR} = 2.39, P < 0.001), and raccoons from urbanized sites were less likely to be seropositive than raccoons in urban open sites (adjusted OR = 0.57, P = 0.04). Raccoons from urban open sites were more likely to be seropositive for T. gondii than raccoons from urbanized sites (adjusted OR = 2.70, P < 0.001), similarly, raccoons from rural open sites were more likely to be seropositive than urbanized raccoons (adjusted OR = 2.81, P < 0.001). Raccoons inhabiting all areas of this urban landscape were commonly exposed to the infectious agents we screened for, some of which pose risks to other wildlife species, humans, and to domestic and captive animal populations. Furthermore, the prevalence of exposure to certain infectious agents (CDV and T. gondii) differed across the landscape, therefore, the risks to humans and domestic species may be variable in different portions of the landscape. The relationship between changes in risk of exposure to infectious agents and land-use warrants further investigation due to the potential impacts on the health and safety of humans and domestic animals. My results indicate that landscape changes from urbanization can influence the relationships between land-use, host population dynamics, and host-pathogen relationships.