Spatial ecology of disease spread in the island fox

Graduation Date

2012

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Natural Resources, Wildlife, 2012

Committee Chair Name

Brian Hudgens

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Rabies, Population density, Humboldt State University -- Theses -- Wildlife, Contact rates, Disease spread, Island fox, Modeling, Canine distemper, Channel Islands, Home range, Urocyon littoralis

Abstract

Diseases are potential threats to wildlife populations worldwide, and recent epidemics have demonstrated their far-reaching impacts. The spread of directly transmitted pathogens is influenced by host contact rates, and host density can alter these contact rates by changing the spatial distribution of host home ranges. I explored how host density might affect the spread of directly transmitted pathogens in Channel Island foxes (Urocyon littoralis) through changes in contact rates, home range size and overlap. I tracked 40 radio-collared foxes at four sites on San Clemente Island, which ranged in density from 2.8±1.28 to 42.8±9.43 foxes/km2. Thirty foxes wore collars that also contained proximity loggers. More overlap correlated with higher rates of contact between neighbors. Foxes at high densities had more neighbors with overlapping home ranges but not an increase in the amount of pair-wise overlap or contact between individual neighbors. I used these home range and contact data to parameterize a spatially explicit model of rabies and canine distemper spread in island foxes. Modeled fox densities, home range sizes and degree of overlap, and contact rates approximated those measured on San Clemente Island. I examined how host density at the point of disease introduction and different vaccination strategies (i.e., no vaccination, random vaccination, or firewall/core area vaccination) might affect disease dynamics. In model simulations, canine distemper spread quicker, infected more animals, and caused a greater reduction in the fox population than rabies due to differences in the length of the prepatent and infectious periods. The introduction of either pathogen to areas of high fox density resulted in more rapid transmission than if the pathogen was introduced at lower densities. Random vaccination was generally the more successful strategy for reducing the number of infected or dead animals from both diseases, and may be the preferable strategy for San Clemente Island. The model parameters with the greatest proportional effect on output were fox contact rates, virus transmissibility, background transmission rate, and the length of the prepatent and infectious periods. This study was the first time island fox contact rates were directly measured and compared to density and home range overlap, and it confirms that overlap is a reliable index of the amount of direct contact between island foxes. Model results can be used to advise conservation efforts aimed at preventing and responding to disease outbreaks in island foxes.

https://scholarworks.calstate.edu/concern/theses/8910jw99s

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