The role of speciation and introgression in local co-occurrence: Eucalyptus in the Grampians Ranges

Background/Question/Methods

Studies of local plant co-occurrence tend to focus on ecological processes (e.g. limiting similarity and habitat filtering), yet evolutionary processes may also be important. Here, we explore the idea that hybridization and introgression—known to be evolutionarily important—also influence present day co-occurrence of Eucalyptus species in the Grampians Ranges, Australia. We define levels of reproductive compatibility based on field observation and patterns of genetic variation, including incongruence between chloroplast DNA and nuclear ribosomal DNA. We model how traits (specific leaf area, height, and seed mass), habitat, and reproductive compatibility explain co-occurrence patterns. 

Results/Conclusions

Functionally similar species co-occurred in plots unless they had intertwined evolutionary histories (i.e. evidence of past introgression and recent hybridization). For example, co-occurring species had similar specific leaf area (SLA) in general, yet reproductively compatible species did not co-occur despite having similar SLA. The negative effect of reproductive compatibility was stronger than the positive effect of SLA similarity on co-occurrence. Results demonstrate the lingering importance of evolutionary processes in present day species assemblages.