Black bears (Ursus americanus) in Alabama have been restricted to a single small population around Mobile since 1920. Recently a second population has been established with natural migrants in the northeastern corner of the state. Both of these populations are small in size leaving them vulnerable to inbreeding depressions if they are not interbreeding with surrounding populations. Therefore it was necessary to explore the level of genetic structure between bears in Alabama and surrounding populations. Bears were extensively sampled from both Alabama populations using hair snares, while samples from surrounding populations were obtained from either management agencies, or other hair snare studies. Population assignment was explored utilizing a Bayesian clustering analysis in program STRUCTURE to assign the division of all regional populations. Once populations were assigned population relationships were visualized utilizing a discriminant analysis of principle components (DAPC). Finally structure between populations was quantified using Fst and G”st pairwise comparisons between all defined populations.
Results/Conclusions
We found that the Mobile population of bears extended into the eastern most parts of Mississippi, however they had high levels of structure with all other populations of bears. No pairwise G”st comparison of Mobile was below 0.708 indicating a high level of structure, which agreed with the DAPC’s findings. The northern Alabama population of bears was similarly assigned as a unique population by STRUCTURE, but G”st showed little structure between it and a population in northern Georgia (0.190). The north Georgia population was assigned by STRUCTURE as a mixture of the north Alabama population and a Tennessee population, indicating it was the stepping stone in an island hopping model of dispersal from TN. Outside of this dispersal relationship the northern Alabama population shows a high level of structure with all other populations with its lowest G”st value being 0.729.
Our findings show that bears in the Mobile region are significantly isolated from other populations and will be at risk of an inbreeding depression if efforts are not made to connect them with other populations. As of yet the northern Alabama population is too new to determine if existing indications of connectivity are from their recent founding or continued interaction.