LB 5-44 - Variation in the spatial co-occurrences of close kin in wild caribou populations

Background/Question/Methods:

As habitats become increasingly fragmented, it is critical to understand how individuals within remaining habitats are connected, both spatially and genetically. For many species living in fission-fusion groups there are both costs and benefits to spatially or socially associating with close relatives. Noninvasive genetic analysis of individuals has proven to be an invaluable tool in conservation biology, allowing the reconstruction of detailed pedigrees for wild populations, where mating data would be otherwise impossible to obtain. Here we studied five populations of wild caribou (Rangifer tarandus), in different habitats across Canada over the winter for 3-11 years. Using noninvasive genetic sampling we developed pedigree networks for each population, including first to third order relationships. We then constructed networks of individual spatial co-occurrence using spatial capture-recapture methods. Using novel multilayer network analysis, we were then able to determine to what degree caribou that co-occurred spatially were related. Using network-based permutations we compared the observed overlap to null models to determine if the observed patterns of overlap occurred significantly more than would be expected by chance.

Results/Conclusions:

We found that caribou populations varied in the extent and classes of familial relationships which shared spatial co-occurrences. In most populations, spatial co-occurrences were greater than expected from the null model only for parent-offspring relationships. A sex-specific analysis of the parent-offspring pairs highlights that this overlap is driven by a strong degree of co-occurrence between mothers and their offspring of either sex. However, in the highest sampled, and most dense pedigree network, we found that significant overlap also existed for both sibling and grandparent-grandchild relationships. Additionally, two populations demonstrated no significant overlap in spatial co-occurrence and any familial relationship. As significant parent-offspring overlap was found to be driven by mother-offspring relationships, and these populations exhibited a low overall number of observed parent-offspring pairs, the lack of overlap in these populations may be an indication of poor calf survival. On the other hand, the higher degree of overlap with more distant relatives seen in some populations may indicate a population lacking appropriate mobility. Thus, our research highlights the importance of understanding the spatial and genetic overlap at the individual level for the conservation of threatened populations.