Esther Dale studies plant diversification as a postdoc at Manaaki Whenua – Landcare Research in Dunedin and the University of Otago, Department of Botany. Her recent publication in the Journal of Biogeography tests biome conservatism in Australian Acacia using species distribution modeling. Esther discusses the implications of her findings, particularly that hyper-diverse Australian Acacia provides a rare example of a plant lineage in which most species occur across multiple biomes.
Esther Dale in the Palm House at the University of Copenhagen Botanical Garden
Institution: Manaaki Whenua – Landcare Research, Dunedin; University of Otago, Department of Botany
Current academic life stage: Postdoc
Research interests: I study plant diversification, focusing on the role of shifts between different biomes in lineage evolution.
Current study system: Australian Acacia—they’re hyper-diverse, with over 1000 species, making them one of the most diverse vascular plant genera globally. Australian Acacia have managed to occupy many different, contrasting ecosystems such as desert and tropical rainforest.
Recent paper in Journal of Biogeography: Dale EE, Larcombe MJ, Lee WG, Higgins, SI (2020). Diversification is decoupled from biome fidelity: Acacia–a case study. Journal of Biogeography, 47(2):538– 552. DOI: 10.1111/jbi.13768
Motivation for the paper: We were interested in examining how plant lineages evolve in relation to the biomes that they occupy. Biome conservatism, the tendency for lineages to remain in their ancestral biome, is regarded as relatively typical in plant lineages. We wanted to explore whether biome conservatism constrains diversification by keeping lineages within a particular biome, if diversification is primarily occurring within biome boundaries, and if diversification is associated with specialisation to a single biome. We decided to use Australian Acacia to test this because it is hyper-diverse (over 1000 species!), it has a published phylogeny, and distribution data were available.
Acacia aneura in Mallee. This vegetation would be classified as Mediterranean (WWF Biomes), Short Low-productivity Non-seasonal (Functional Biomes), or Eremaean (Crisp Biomes and González-Orozco Biomes). Photo credit: Matthew Larcombe.
Key methodologies: We used species distribution modelling to identify which biomes each species occurs in. We had noticed with the distributional data that some biomes were under-sampled, which might make species seem more specialised to certain biomes than they are in reality. To minimise this source of bias, we used predicted distributions rather than distribution records to determine the biomes occupied. In addition, there are a variety of different biome maps with different numbers of biomes. Previous biome conservatism work has used a variety of different biome maps and we thought it was likely that the biome typology used would influence the conclusions being drawn. We used four different biome typologies to check that our findings were robust over multiple different biome concepts.
(left) Esther at the Brisbane Botanic Gardens Mt Coot-tha examining Acacia disparrima. (right) Esther at Kings Plains National Park, New South Wales. The vegetation in this area would be classified as Temperate Forest (WWF Biomes), Tall High-productivity Non-seasonal (Functional Biomes), Southeastern Temperate (Crisp Biomes), or Euronotian (González-Orozco Biomes). Photo credit: Zoë Stone.
Unexpected challenges: In contrast to the expectation under biome conservatism, we observed that most species (91%) occurred in multiple biomes. This was quite surprising because it contrasts some previous work demonstrating biome conservatism as widespread. It indicates that specialisation of species to a single biome cannot be assumed, and analyses examining biome shifts and biome conservatism should allow for species that occupy multiple biomes. The main challenge with this research was the size of the dataset. It involved 481 species, 151735 occurrence records, and global environmental data layers with a 1 km resolution, meaning we needed to be efficient with our analyses. Most of us working on this project hadn’t worked on Australian species before and were not familiar with the history of the flora or climate, so it was challenging taking on such a characteristically Australian group without much experience of Australian ecosystems. However, it was probably also useful—we hope—to be able to contribute a fresh perspective.
Major result and contribution to the field: We found a consistent pattern of cross-biome diversification with all four biome typologies. Higher diversity clades had greater niche size, indicating that diversification is linked to occupying new niche space rather than partitioning the ancestral niche. Our work demonstrates that Acacia can easily overcome biome boundaries, and diversification in Acacia is not constrained by biome conservatism. This contributes a rare example of a lineage where most species occur in many biomes, with diversification occurring across biome boundaries. Our findings also indicate that lineages can have many species that occur in multiple biomes, so analyses should allow for species that occupy multiple biomes.
What are the next steps? We are interested in applying what we’ve learned from looking at Acacia, with its large spatial and taxonomic scale, to New Zealand plant lineages. We are keen to follow on from these findings by exploring how diversification is affected by new biomes appearing, and whether biome shifts are associated with trait innovations. New Zealand will provide an interesting contrast to our Acacia work because there are fewer biomes and smaller focal lineages. In New Zealand there has been a clear sequence of different biomes becoming available, which presents an excellent opportunity for examining the role of new biomes and biome shifts in lineage evolution. New Zealand is a fantastic system for testing hypotheses about plant evolution because of the quirks of the flora, like high incidences of polyploidy, divarication, and small inconspicuous flowers, and its isolation, making it a natural experiment in evolution.
If you could study any organism on Earth, what would it be and why? I would love to be able to study subantarctic megaherbs. The subantarctic islands are known for their megaherbs, which tend to be much larger and have flowers that are brighter in colour than their New Zealand mainland relatives. It would be fun to examine their evolutionary history to understand how they have adapted to the conditions in the subantarctics, and what selection pressures are driving these changes.
Any other little gems you would like to share? This type of work would not be possible without the excellent body of herbarium specimens in Australia, so a big thanks to all the collectors, herbarium curators, and the Atlas of Living Australia who do such important work!
Eucalyptus regnans forest in Gippsland Victoria. This vegetation would be classified as Temperate forest (WWF Biomes), Tall High-productivity Non-seasonal (Functional Biomes), Southeastern Temperate (Crisp Biomes), or Euronotian (González-Orozco Biomes). Photo credit: Matthew Larcombe.