Bighorn sheep populations are subject to recurrent outbreaks of infectious pneumonia, which vary dramatically in severity. Here, we empirically examine the role that bighorn sheep social ecology plays in determining that severity. Our results indicate that some features of bighorn sheep social structures (for example, population-level substructuring, and limited direct contact between individuals of certain demographic groups) may slow endemic disease transmission in several important ways. Additionally, we present a preliminary analysis relating bighorn sheep population size to population-level spatial ecology, a key step in formalizing how population size relates to the risk of pathogen introduction.
Results/Conclusions
First, we present evidence that disease transmission is sequestered into particular ewe-lamb nursery groups, which remain relatively consistent in size even as population sizes decline. Second, we use empirically measured contact networks, known infection statuses, and disease outcomes to infer force of infection exerted by individuals in different demographic groups. Our results suggest a limited transmission role for infected but non-reproductive animals. Finally, we show preliminary results describing how social network modularity relates to land use patterns in several bighorn herds, with an eye toward understanding how changes in population size might alter population-level space use, and consequently, the risk of pathogen introduction. Taken together, our work suggests that host social ecology plays an important role in shaping both spillover risk and long-term pathogen persistence patterns and transmission dynamics in the bighorn sheep pneumonia system.