Fuzzy structure and spatial dynamics of a declining woodland caribou population

Examining both spatial and temporal variation can provide insights into pop ulation limiting factors. We investigated the relative spatial and temporal changes in range use and mortality within the Red Wine Mountains caribou h erd, a population that declined by approximately 75% from the 1980s to the 1990s, To extract the spatial structure of the population, we applied fuzzy cluster analysis, a method which assigns graded group membership, to space use of radio-tracked adult females, and compared these results to a hard c lassification based on sums-of-squares agglomerative clustering. Both appro aches revealed four subpopulations. Based on the subpopulation assignments, we apportioned the number of animals, radio-days, calving events and morta lities across subpopulations before and after the decline. The results indi cated that, as the herd declined, subpopulations were disproportionately af fected. In general, subpopulations with the greatest range overlap with mig ratory caribou from the George River herd experienced comparative reduction s in activity and increased mortality. The subpopulation with the least ove rlap exhibited the converse pattern. The infra-population imbalances were m ore pronounced when hard clustering was employed. Our results reiterate tha t refugia from other ungulates may be important in the persistence of taiga dwelling caribou, We propose that changes across time and space are valuab le assays of localised demographic change, especially where individuals exh ibit spatial hyperdispersion and site fidelity.