Interactions between density, home range behaviors, and contact rates in the Channel Island fox (Urocyon littoralis).

Jessica N Sanchez,Brian R Hudgens

doi:10.1002/ece3.1533

Abstract

Many of the mechanisms underlying density-dependent regulation of populations, including contest competition and disease spread, depend on contact among neighboring animals. Understanding how variation in population density influences the frequency of contact among neighboring animals is therefore an important aspect to understanding the mechanisms underlying, and ecological consequences of, density-dependent regulation. However, contact rates are difficult to measure in the field and may be influenced by density through multiple pathways. This study explored how local density affects contact rates among Channel Island foxes (Urocyon littoralis) through two pathways: changes in home range size and changes in home range overlap. We tracked 40 radio-collared foxes at four sites on San Clemente Island, California. Fox densities at the four sites ranged from 2.8 ± 1.28 to 42.8 ± 9.43 foxes/km2. Higher fox densities were correlated with smaller home ranges (R2 = 0.526, F1,38 = 42.19, P < 0.001). Thirty foxes wore collars that also contained proximity loggers, which recorded the time and duration of occasions when collared foxes were within 5 m of one another. Contact rates between neighboring fox dyads were positively correlated with home range overlap (R2 = 0.341, P = 0.008), but not fox density (R2 = 0.012, P = 0.976). Individuals at high densities had more collared neighbors with overlapping home ranges (R2 = 0.123, P = 0.026) but not an increase in the amount of contact between individual neighbors. This study was the first time contact rates were directly measured and compared to density and home range overlap. Results suggest that foxes exhibit a threshold in their degree of tolerance for neighbors, overlap is a reliable index of the amount of direct contact between island foxes, and disease transmission rates will likely scale with fox density.

Highlights

This study explored how population density affects individual contact rates through variations in home range size and overlap in the Channel Island fox (Urocyon littoralis) on San Clemente Island (SCI), California (Fig. 2)
Our study confirmed two intuitive patterns of home range behaviors: local fox density was negatively correlated with home range size, and home range overlap was positively correlated with contact rates (Fig. 7)
We found that home range overlap and contact rates among unrelated neighboring dyads were not correlated with local fox density, but there was a weak positive relationship between density and the number of collared a 2015 The Authors

Summary

Introduction

Close contacts among individuals influence the spread of directly transmitted pathogens (Keeling 1999; Altizer et al 2003; Bo€hm et al 2009; Cross et al 2009; Hamede et al 2009), competition and predation risk (Mills and Gorman 1997; Berger and Gese 2007), resource utilization and habitat use among species (Major and Sherburne 1987; Weissinger et al 2009), determine the organization of social groups and mating patterns (Tucker et al 1993; Ramsey et al 2002), and explain reproductive phenomena (Ordiz et al 2008). Contacts among individuals or groups are likely to be influenced by various aspects of a species’ ecology, such as the degree to which territories or areas of exclusive use are maintained, the number of individuals with neighboring (adjacent) home ranges, and the amount of contact those neighbors have with one another (Woodroffe 1999). These factors in turn depend on the density of the population, which can influence contact rates by altering home range sizes and the amount of overlap between home ranges (McCallum et al 2001).

Methods

Results

Conclusion