Temporal turnover of mammal communities in response to climate change in different topographical landscapes
While it is clear that α and β-diversity tend to be higher in topographically complex regions, it is less clear whether these regions maintain a stable community structure through time. Topographical heterogeneity may provide a buffer against the effects of climate change, allowing communities to persist in the same region by moving along the elevation gradient, or into refugia. In contrast, less complex regions will not provide a strong buffer against climate change and should show larger differences in community structure over time because species will be forced to migrate away to suitable habitat. This study will explore patterns of mammal community turnover in landscapes with different degrees of topographical complexity. Here, I use the FAUNMAP database to determine whether mammal assemblages in topographically heterogeneous regions remain more stable through time despite climate change, as compared to those in flatlands. Six topographically complex regions, and four less complex regions were identified in the USA and Canada. Turnover between three time bins was analysed: 52-25 kyBP (pre-glacial), 25-15 kyBP (full-glacial), and 15-10 kyBP (post-glacial). The Sorenson-Dice Index was used to measure assemblage similarity for each region across the three time bins.
A two-way ANOVA showed that, on average, assemblages in more topographically complex regions were significantly (p < 0.05) more similar across the three turnover intervals than assemblages located in lowlands and plains. Regardless of topographical complexity, communities were on average most similar between the full-glacial and post-glacial, and least similar between pre-glacial and full-glacial time intervals; however, these differences were not significant. There was no significant interaction effect between topography and the turnover interval. This suggests that topographical heterogeneity is indeed playing a role in maintaining community stability. Complex topography appears to be forming a buffer to climate change, facilitating the movement of species across elevation gradients to more suitable habitats within the region. In contrast, species in less complex regions are likely moving great distances to find suitable habitat, or going locally extinct. In order to understand the mechanisms of this turnover, a functional analysis will be conducted. Here, changes in the functional hypervolume will be analyzed to determine which functional groups are driving turnover in both types of landscapes.