Sex-specific differences in familial networks, dispersal and reproductive success are driven by heterogeneity in density

Background/Question/Methods

Density is an important demographic parameter that is commonly overlooked in studies of wild populations. We examined a range of spatially explicit demographic parameters in a wild population of a cryptic ungulate, boreal woodland caribou (Rangifer tarandus caribou). Using noninvasive genetic sampling, we used spatial capture-recapture with covariates to estimate density of boreal woodland caribou across a 108 806 km2 study area. We then created a familial network from reconstructed parent-offspring relationships and determined whether spatial density influenced sex-specific dispersal distance, individual reproductive success, and female pregnancy status.

Results/Conclusions

We showed that caribou density varied greatly, leading to variation in dispersal distances, with offspring moving shorter distances when parents were found in higher density areas. This significantly affected both male and female reproductive success, with males showing positive density dependence, and females showing negative density dependence. No differences were found in pregnancy rates of females occurring in high- and low-density areas. Familial network reconstruction using genetic data showed that demographic parameters of both males and females were density-dependent. Although high density areas do reflect good quality caribou habitat, the observed decreased dispersal rates and lower female recruitment rates suggest that remnant habitat patches may trigger positive feedbacks.