Intraspecific divergence associated with a biogeographic barrier and climatic models show future threats and long-term decline of a rainforest conifer

Abstract

A capacity to foresee the shift in species’ range and the demographic response to future climate change is integral to effective conservation planning. Here we model the future climate-driven range shift, and compare it with past range shift, along a latitudinal gradient in two population groups of a late-successional rainforest conifer (Podocarpus elatus), genetically differentiated over the Clarence River Corridor biogeographic barrier (Northern NSW, East Australian Rainforests). Climate envelope modelling of the past-current-future distributions of the two groups and a coalescent-based isolation-with-migration model investigated divergence times and effective population sizes among the current genetic disjunctions in the species. This suggests differential range shift (i.e. expansion in the north and contraction in the south) will continue in the future, with a southern range shift also occurring in both climatic models. The origin of the Clarence River Corridor dividing the two population groups was inferred by molecular analysis to be prior to the last glacial maximum (LGM). Another divergence in the south (19 ka) is indicative of slow consistent habitat contractions since the LGM (21 ka). We recommend the southern and Macleay Overlap Zone (far-eastern Australia) populations as priority areas for protection based upon intraspecific diversity and past-current-future habitat suitability. The integrated approach shows that this widely distributed species is more at risk than expected from current climate change and other anthropogenic effects.