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Why are large fruited species rare?

Why are Australian rainforest species distributed and assembled the way they are?

Why do some species have limited distributions, and why are regions such as the Nightcap and Border Ranges in NSW and the Wet Tropics in Queensland more diverse than others? 

The dispersal of fruit (and seed) by animals is a crucial component of the distribution and dynamics of plants, the structure of forests, and the maintenance of landscape-level diversity. We found that rainforest plants with small fleshy fruits (less than 3 centimeters in diameter) are generally more common and distributed more widely than species with larger fruits. This is particularly true in southern Queensland and northern New South Wales, where the number of animals capable of ingesting and dispersing larger fruits is limited.  
 
We also found that in both the tropics and subtropics, the richness of large-fruited rainforest species tracks the distribution of environmentally stable refugia. This suggests that many rainforest areas are (or have been) too small and/or too locally dissected to retain animals capable of supporting the dispersal of species with large fruits. For example, in the subtropics many large-fruited species belonging to the family Lauraceae (the family of the avocado) and Sapotaceae are rare and highly restricted in distribution.
 
Since subtropical rainforests do not have animals able to disperse large-fruited species between forest remnants (such as Cassowaries in tropical rainforests), specific management strategies targeting large-fruited taxa need to be considered. Based on well-informed genetic and environmental guidelines, these include population augmentation (where individuals from different populations are mixed to increase diversity and fitness) and assisted migration (where new populations are established in suitable habitat outside their current range).

Current research

We use the latest genetic tools in combination with ecological and distributional information to understand how dispersal impacts the distribution and assembly of rainforest species.

Some of the questions that we are asking are:

  1. How long have disjunct populations of large-fruited species been isolated, and what geological events have contributed to their current distributional patterns?
  2. What is the timing and impact of the extinction of megafauna (large animals that use to disperse large-fruited species but are now extinct) in Australia?
  3. What is the role of Indigenous people in dispersing rainforest species?
  4. What is the impact of the dispersal of small-fruited species from southeastern Asia (Sunda) into Australia?

Some of our relevant publications:

  1. Yap JYS, Rossetto M, Costion C, Crayn D, Kooyman R, Richardson J, Henry R (2017) Filters of floristic exchange: how traits and climate shape the invasion of Sahul from Sunda. Journal of Biogeography
  2. Rossetto M, Ens EJ, Honingh T, Wilson PD, Yap JYS, Costello O, Round ER, Bowern G (2017) From Songlines to genomes: prehistoric assisted migration of a rain forest tree by Australian Aboriginal people. PLOS ONE 12(11): e0186663
  3. Worth JRP, Holland BR, Beeton NJ, Schönfeld B, Rossetto M, Vaillancourt RE, Jordan GJ (2017) Habitat type and dispersal mode underlie the capacity for plant migration across an intermittent seaway. Annals of Botany 120(4): 539–549
  4. Rossetto M, Yap JYS, Kooyman R, Laffan S (2015) From ratites to rats: the size of fleshy fruits shapes species distributions and continental rainforest assembly. Proceedings of the Royal Society B 282:20151998.
  5. Rossetto M, McPherson H, Siow J, Kooyman R, van der Merwe M, Wilson PD (2015) Where did all the trees come from? A novel multidisciplinary approach reveals the impacts of biogeographic history and functional diversity on rain forest assembly. Journal of Biogeography 42: 2172-2186.
  6. Heslewood MM, Lowe AJ, Crayn DM, Rossetto M (2014) Contrasting levels of connectivity and localised persistence characterise the latitudinal distribution of a wind-dispersed rainforest canopy tree. Genetica 142(3): 251-264.
  7. Rossetto M, Crayn D, Ford A, Mellick R, Sommerville K (2009) The influence of environment and life-history traits on the distribution of genes and individuals: a comparative study of 11 rainforest trees. Molecular Ecology 18: 1422-1438.
  8. Rossetto M, Kooyman R, Sherwin W, Jones R (2008) Dispersal limitations, rather than bottlenecks or habitat specificity, can restrict the distribution of rare and endemic rainforest trees. American Journal of Botany 95:321-329.
  9. Rossetto M (2008) From populations to communities: understanding changes in rainforest diversity through the integration of molecular, ecological and environmental data. Telopea 12(1): 47-58.
  10. Rossetto M, Crayn D, Ford A, Ridgeway P, Rymer P (2007) The comparative study of range-wide genetic structure across related, co-distributed rainforest trees reveals contrasting evolutionary histories. Australian Journal of Botany 55(4): 416-424.
  11. Rossetto M, Kooyman RM (2005) The tension between dispersal and persistence regulates the current distribution of rare paleo-endemic rainforest flora: a case study. Journal of Ecology 93: 906-917.
  12. Rossetto M, Gross CL, Jones R, Hunter J (2004) The impact of clonality on an endangered tree (Elaeocarpus williamsianus) in a fragmented rainforest. Biological Conservation 117(1): 33-39.
  13. Rossetto M, Jones R, Hunter J (2004) Genetic effects of rainforest fragmentation in an early successional tree (Elaeocarpus grandis). Heredity 93(6): 610-618.