Habitat alterations and population isolation: The caribou case

Human-induced habitat alterations are one of the biggest threats to biodiversity globally. Habitat fragmentation particularly has been linked to increased risk of extirpations through decreases in dispersal leading to population isolation. Isolation of populations may be a result of three major scenarios: (1) Isolation by Distance (IBD), (2) Isolation by Environment (IBE), and (3) Isolation by Barrier (IBB). Recent results have shown that caribou (Rangifer tarandus), a threatened habitat specialist, are experiencing population isolation in Western Canada. Our work aims to discover drivers of population isolation of caribou owing to three potential hypotheses: Population isolation of caribou is a result of (H1) lack of food and shelter in the areas between habitat fragments, (H2) predation pressure and human infrastructure, or (H3) physical barriers to dispersal (roads, cutblocks, and non-road linear features), along with the null (H0): Isolation by Distance (IBD). Using Resource Selection Functions (RSFs) and Least-Cost Path analysis (LCP), cost distances associate with travel between habitat patches were created and compared to genetic distance between individuals using partial Mantel tests to understand which factors are driving population isolation in British Columbia’s caribou. Here we show that genetic patterns of isolation in caribou can be explained by a combination of geographic distance (IBD) and habitat (un)suitability in the areas between know population ranges –i.e. a form of IBE. Our findings demonstrate that habitat preferences are dictated by forest stand age (older forests), slope (flatter), and land cover type (open lichen woodlands and mixed conifer forests for example). Habitat preferences also differed seasonally, reflecting specific requirements linked to caribou life cycles Each additional isolation hypotheses (above) were also supported, but likely acting simultaneously; and we are using casual modeling to rank isolation factors. Using RSF models to create resistant surfaces allowed for the discovery of corridors of conservation concern. Our results allow for a better understanding of the relationship between loss of critical habitat, habitat fragmentation, and isolation of populations. Additionally, defining key ecological features that lead to the isolation of populations allows for targeted measures for the conservation of caribou, and of other sympatric species. Finally, our project originally links habitat to affected genetic diversity of species and is transferable to other terrestrial animals also impacted by fragmentation.