Botanic Gardens Trust, Sydney, Australia

Podocarpus elatus (Podocarpaceae) - Quaternary Climate Change

Rohan Mellick - PhD student, The University of Adelaide; Dr M Rossetto, Principal Research Scientist and Manager, Evolutionary Ecology

This year has been spent completing my thesis and writing two research papers. In Mellick et al. (2012) we found the effect of the last glacial cycle had not been uniform across the range of the broadly distributed rain forest tree, Podocarpus elatus (R.Br. ex Endl.). Niche modelling inferred the northern distributional region persisted through the last glacial maximum (LGM) in small refugial areas, which during post-glacial periods has expanded. Conversely the southern range followed the opposite trend and has contracted since the LGM (21 Ka), but overall maintained greater genetic diversity (Fig 1).

Coalescence-based analyses of molecular data support these differential dynamics and infer regional gene flow, the origin of genetic boundaries and expansion/contraction dynamics to provide information with regard to community response to climate cycles. By combining molecular and environmental niche modelling evidence, the study undermines the general assumption that broadly distributed species respond in a uniform way to climate change.
 
Mellick et al. (submitted) infers the origin of the Clarence River Corridor (CRC) dividing the population groups prior to the LGM. A later divergence in the south (19 Ka) is indicative of slow consistent habitat contractions in the south since the LGM. The study predicts future distribution of genetic diversity in the species and indicates areas at increased risk of localised extinction. We recommend the Macleay Overlap Zone as a priority area for protection based upon intraspecific diversity and past-current-future habitat suitability. This study identifies the need for conservation of natural range shift and migration processes to ensure adaptive potential, and suggests that the future design of habitat corridors could take on a broader evolutionary application by linking fragmented habitats along predicted avenues of range shift. Furthermore, understanding natural gene flow patterns will allow for genotype selection and assisted migration along these avenues.

References

Mellick R, Lowe A, Allen CD, Hill RS, Rossetto M (2012). Palaeodistribution modelling and genetic evidence highlight differential post-glacial range shifts of a rain forest conifer distributed across a broad latitudinal gradient. Journal of Biogeography.

Mellick R, Rossetto M, Allen C, Wilson PD, Hill RS, Lowe A (submitted). Molecular and habitat suitability models highlight future threats and long-term decline of a common rainforest conifer. Biological Conservation.

 

 

 

 

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