Effects of Urban Borders on Synanthropic Mesopredator Movement and Risk of Toxoplasma Gondii Infection in the Protected Lands of Key Largo, Florida USA

Author

Kelly A. Crandall, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2024

Degree Name

Master of Science

Department

Forestry

First Advisor

Pease, Brent

Abstract

Protected lands are an important source of food, shelter, and reproductive opportunities for wildlife, especially in urbanizing landscapes. When urban development abuts the edges of protected lands, synanthropic species can alter their foraging behaviors and movement to utilize human-supplemented resources throughout the urban-wild interface. Therefore, urban edges on protected lands can have pronounced effects on animal movement and ecosystem function. There is also increased risk of disease transmission where high densities of wild animals exist, or where domestic animals and wild species are interacting. In particular, members of the family Felidae, including domestic cats (Felis catus), can transmit the pathogenic parasite, Toxoplasma gondii (henceforth T. gondii) through their feces. Capable of infecting any warm-blooded host species, infection with T. gondii has been proven to cause increased risk-taking behaviors, stillbirths and congenital birth defects, and mortality in humans and a variety of wildlife species. Northern raccoons (Procyon lotor) and Virginia opossums (Didelphis virginiana) are urban adaptive species who often benefit from human-supplemented food sources such as unsecured garbage, and outdoor pet food, and may be exposed to T. gondii more frequently if they are utilizing resources close to cats. To investigate how urban edges of protected lands affect the movement and infection risk for urban-adapted mesopredators, I captured and attached GPS collars to opossums and raccoons between April 2022 and October 2023 in northern Key Largo, FL, USA, a protected area with large contiguous patches of undisturbed land cover adjacent to two distinct urban areas with high outdoor cat densities and available human-supplemented food resources. Using GPS collar data, I estimated home ranges and third-order resource selection of 27 raccoons and 12 opossums from Key Largo, FL. The average home range of opossums were 20.51 ha (14.12 SE) which was significantly smaller than raccoons (137.01 ha, 10.74 SE, t37 = -2.70, p = 0.01). The proportion of urban development in an individual’s home range was the most influential factor associated with home range size, followed by species and sex. Individuals with greater proportions of residential neighborhoods and commercial areas in their home ranges were associated with smaller home ranges. Third-order resource selection functions identified both mesopredator species using residential and commercial land use areas significantly more than they were available on the landscape. To survey for T. gondii infections, I collected blood samples from all the captured raccoons and performed a direct modified agglutination test (MAT) to detect antibodies for T. gondii. To understand how human-supplemented foods could be affected exposure rates, I collected hair samples from all raccoons and analyzed the stable carbon isotope ratios, so that higher ratios of carbon were equated to greater intake of non-natural, human-supplemented food resources. 67.7% (21/31; 95% CI: 51.3–84.2%) of the raccoons tested positive for T. gondii antibodies, and the proportion of urban development in an individual’s home range was the best predictor for infection. A multinomial regression analysis indicated that raccoons with higher levels of antibodies were also likely to have a majority “non-wild” diet based on δ13C values from a stable carbon isotope analysis. These results suggest the primary route of parasite transmission is contact with domestic cats, which may be exacerbated by the exploitation of human-supplemented food in urban areas. The Florida Keys are currently facing mammal population declines tied to Burmese pythons (Python bivitattus) and outdoor cat predations, and management policies that decrease the circulation of T. gondii oocysts in the environment are important to bolstering the fitness of these island-dwelling populations. Decreased reproductive success or behavioral changes that increase risk of predation could spell catastrophic for these mesopredator populations that are following in the footsteps of their Everglades counterparts, and at risk of extirpation on Key Largo. I recorded a systemic reduction of home range sizes on the urban edges of the protected areas of Key Largo, which often corresponds with higher densities of animals, which may increase probability of disease transmission, especially when the urban borders support populations of feral domestic species. As urbanization increases and the distance between wild lands and human disturbance decreases, it is increasingly important to study the mechanisms of how urban development on the edges of protected areas affect the ecology of wildlife species.