Heterogeneity in social network connections is density-dependent: implications for disease dynamics in a gregarious ungulate

Abstract

Incorporating host behavioral variation into epidemiological models is important for predicting host-pathogen dynamics. Animals living at high densities or with many strong social connections are predicted to have greater risk of acquiring pathogens. Using social network analysis, we tested the hypothesis that variation in the strength of social connections would influence simulated elk (Cervus canadensis) pathogen dynamics. We quantified fine-scale social connections for captive elk at three experimentally manipulated densities and wild elk at two natural densities. We applied susceptible-infected epidemiological models to networks to infer the relationship between fine-scale host sociality and simulated pathogen dynamics. Networks were filtered based on four association thresholds to determine how variation in the strength of social connections influenced pathogen dynamics. Our simulations suggest that social behavior interacts with population density to predict pathogen dynamics, but this effect was sex-specific. For both males and females at higher density, elk had strong social connections, resulting in higher number of infected individuals. We observed differences in social connections across density, and these results translated to our simulations, which predicted density-dependent pathogen dynamics for captive and wild elk networks. Our results highlight host social behavior as a potential mechanism driving variation in the relationship between population density and pathogen dynamics. Elk are reservoir hosts for numerous emerging infectious diseases, and our models suggest that density-dependent host social behavior could influence pathogen dynamics in elk social networks. Animal population density can influence transmission of parasites and pathogens, but variation in social connections at different densities could impact this relationship. Using social network analysis and epidemiological simulations, we tested the hypothesis that density-dependent variation in social connections would influence pathogen dynamics using captive and free-ranging populations of elk (Cervus elaphus). For all elk groups, simulated number of infected individuals increased with social connectedness. In addition, our simulations suggest that social connectedness interacts with population density to predict number of infected individuals, but this effect was sex-specific. For males and females at high density, elk had strong social connections, resulting in more infected individuals; this relationship was linear for males and non-linear for females. Taken together, our results suggest fine-scale measures of social behavior vary with population density, a result which could have implications for pathogen dynamics.