Abstract
Dispersal facilitates population health and maintains resilience in species via gene flow. Adult dispersal occurs in some species, is often facultative, and is poorly understood, but has important management implications, particularly with respect to disease spread. Although the role of adult dispersal in spreading disease has been documented, the potential influence of disease on dispersal has received little attention. African buffalo (Syncerus caffer) are wide‐ranging and harbor many pathogens that can affect nearby livestock. Dispersal of adult buffalo has been described, but ecological and social drivers of buffalo dispersal are poorly understood. We investigated drivers of adult buffalo dispersal during a 4‐year longitudinal study at Kruger National Park, South Africa. We monitored the spatial movement of 304 female buffalo in two focal areas using satellite and radio collars, capturing each buffalo every 6 months to assess animal traits and disease status. We used generalized linear mixed models to determine whether likelihood of dispersal for individual female buffalo was influenced by animal traits, herd identity, environmental variables, gastrointestinal parasites, or microparasite infections. The likelihood and drivers of buffalo dispersal varied by herd, area, and year. In the Lower Sabie herd, where resources were abundant, younger individuals were more likely to disperse, with most dispersal occurring in the early wet season and during an unusually dry year, 2009. In the resource‐poor Crocodile Bridge area, buffalo in poor condition were most likely to disperse. Our findings suggest that dispersal of female buffalo is driven by either seasonal (Lower Sabie) or perhaps social (Crocodile Bridge) resource restriction, indicating resource limitation and dispersal decisions are tightly linked for this social ungulate. We found no direct effects of infections on buffalo dispersal, assuaging fears that highly infectious individuals might be more prone to dispersing, which could accelerate the spatial spread of infectious diseases.
Highlights
Dispersal is an essential life‐history trait in animals, which functions as a mechanism for avoiding inbreeding and finding usable habitats (Bowler & Benton, 2005; Clobert, Danchin, Dhondt, & Nichols, 2001; Kokko & López‐Supulcre, 2006)
Maximum cumulative weight (Ʃ wi) or relative importance for each predictor variable is 1; explanatory variables varied by data set but included condition, age, pregnancy status, lactation status, season, year, strongyle and coccidia burden, schisto and bovine tuberculosis and brucellosis infection status
For the larger data set with the reduced set of variables, we used to predict the effects of animal traits, reproductive status, environmental variables, on probability of dispersal we found that across study regions, body condition, age, herd identity, season, and year contributed to variation in dispersal (Table 4)
Summary
Dispersal is an essential life‐history trait in animals, which functions as a mechanism for avoiding inbreeding and finding usable habitats (Bowler & Benton, 2005; Clobert, Danchin, Dhondt, & Nichols, 2001; Kokko & López‐Supulcre, 2006). Infectious disease and possible interactions with dispersal are important for this species given the potential for disease interactions with livestock and resulting human‐wildlife conflict Macroparasites, such as bovine tuberculosis and brucellosis may influence individual condition (Caron, Cross, & du Toit, 2003; Gorsich, Ezenwa, Cross, Bengis, & Jolles, 2015), leading to indirect effects on dispersal behavior. Male African buffalo could be regarded as natal dispersers, given that observational and genetic studies suggest that almost all male buffalo disperse away from their natal herds (van Hooft et al, 2003; Prins, 1996; Sinclair, 1977), behavior of females differs. We had no clear a priori reason to predict that individual infections like microparasites, including Mycobacterium bovis (causative agent of bovine tuberculosis) and Brucella abortus (causative agent of brucellosis) would influence dispersal, we evaluated those relationships due to the critical implications of dispersal‐disease interactions for wildlife‐livestock relationships
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