Species traits as filters of climate-induced range expansion
As climate warms, species are expected to move poleward or up in elevation to track the environmental conditions to which they are most adapted. However, this movement and the subsequent colonization of new habitat may be affected by species-specific habitat affinities and life history traits that facilitate or impede range expansion. Even if the “thermal envelope” is ideal, the vegetation conditions or other environmental parameters may not be conducive. Similarly, traits such as wingspan or voltinism may act as a filter in defining which species can successfully colonize new regions. We used 106 well-sampled butterfly species to track changes over time in Canada, comparing data from 1880-1970 and 1985-2012. The country was divided into a set of grid cells at a 4 degree resolution and species distribution changes were assessed within each grid cell. Because there were differences in the total number of species observed between the two time periods, we used a standardized difference measure to assess changes in relative abundance for each species. We modeled the standardized difference as a function of latitude and species traits, including wingspan, habitat preference (open, closed, or edge), moisture affinity (xeric, mesic, or both), and voltinism.
Species with larger wingspans and larger numbers of generations per year showed positive trends in abundance. Generalist species also showed increasing trends relative to those that were more specialized in habitat requirements. We examined whether the latitude where a species had been observed increased between these two time periods and modeled the probability that a species had moved north as a function of these life history traits. Species associated with xeric habitats had ~6 times higher odds than those associated with mesic habitat to have moved northward between the two time periods.