In order to conserve biodiversity and predict responses to global change, understanding the drivers of genetic variation and their relative importance is essential. In this paper, researchers presented a phylogeographic framework for testing the contributions of historical climatic shifts versus the positions of populations within species ranges in shaping genetic diversity among North American plants.
By analysing genetic data from 1,400 populations of 91 native North American plants that flower (angiosperms) and those that do not (gymnosperms), the authors derived summary statistics estimating levels of genetic diversity and population-specific differentiation.
They then used GBIF-mediated occurrences to produce species distribution models (SDM) representing the current climate and conditions at the Last Glacial Maximum (LGM, ~22,000 years ago). In addition to ecological suitability, the models were used to quantify distances to range edges and potential glacial refugia for each genetic population.
Combining the genetic statistics with the output of the SDMs, the authors found that genetic diversity significantly decreased as distance to potential glacial refugia increased. Likewise, as the suitability of a population's LGM habitat increased, so did the corresponding genetic diversity.
The analysis also demonstrated a clear relationship between distance to range edge and suitability under current climatic conditions, accompanied by a significant increase in genetic diversity. While providing clear support for demographic effects related to the so-called "central marginal hypothesis," the study's overall results suggest that history and demography have roughly equivalent importance in shaping genetic variation.