Botanic Gardens Trust, Sydney, Australia

Conservation genetics

Dr Maurizio Rossetto, Senior Research Scientist, Manager Evolution and Ecology

Australian rainforests contain considerable levels of biodiversity despite representing only a small proportion of the continental land-mass. Broad-leaved vegetation has endured considerable stress during the aridification of the continent in the last 10 Mya, with the remaining refugial areas being further strained during the climatic instability of the Quaternary. An important challenge of understanding differences in species survival is to gain an insight into the relationship between ecology and evolution. A reconstruction of temporal changes in population dynamics across diverse co-distributed taxa can yield generalities about evolutionary constraints and differential success.

In a range of separate studies (involving numerous postgraduate students and external collaborators), we gathered molecular, environmental and functional data from over 15 rainforest tree species distributed along the eastern coast of Australia. Our overall aim is to understand what makes some species more successful than others. We found some interesting trends explaining current distributions, in particular in relation to the tension between persistence and dispersal, and discovered that interacting factors can impact differently across regional communities.

Our research shows that while advanced resprouting mechanisms can stabilise family size variance and maintain genetic diversity even in small populations for some species (e.g. Eidothea hardeniana), extensive clonality and apomictic reproduction can significantly decrease the available genetic pool (e.g. Elaeocarpus williamsianus and Syzygium paniculatum). We also found that small changes in fruit morphology can significantly affect the dispersal potential of species. For instance, in NSW the absence of large frugivores restricts the dispersal (and consequently distribution range and between-population connectivity) of species with large fruits (e.g. Elaeocarpus sedentarius). Conversely, in a study on 11 local elaeocarp species, we showed that fruit size does not affect connectivity and dispersal potential in the Australian Wet Tropics, where a greater number of dispersal organisms survive.

Habitat preference also impacts differently on the distribution of species. We are finding that upland species tend to have narrower genetic diversity and greater between-population differentiation than lowland species. However, contrary to previous belief, we have increasing evidence suggesting that, in some groups at least (e.g. Elaeocarpus and Ceratopetalum), competitiveness at altitude is more closely associated with adaptation to poorer soils than with adaptation to cooler climates.

Finally, in a current collaboration (R. Kooyman; Macquarie University) we are exploring how rain forest diversity gradients are influenced by evolutionary factors. We are assessing how local, regional and continental assemblages are limited by the phylo-conservatism of the southern rainforest flora and by landscape-level environmental gradients. This way, we aim to elucidate the underlying drivers of functional variation and assemblage in Australian rainforests. Exploring evolutionary interpretations of functional diversity in community assembly is a critical approach for understanding the influence of local-factor variability on biodiversity. 

Such insights will help us understand how rainforest trees respond to environmental and climatic heterogeneity, and how high levels of biodiversity (that include a considerable number of unique paleo-endemics) are maintained within small remnants of a once-dominant vegetation type. In the long-term this knowledge will underpin management strategies that attempt to anticipate the likely response of ecological communities to environmental and climatic change.





Elaeocarpus sedentarius immature fruit at Botanic Gardens Trust. Photo: M. Rossetto

Eidothea hardeniana  in flower at Botanic Gardens Trust. Photo: M. Rossetto

A study on 11 Elaeocarpus species from the Wet Tropics (photo: various contributors)