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Southern hemisphere botanical ecosystems
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RESEARCH ARTICLE
Contents Vol 55(6)

Large seeds, extinct vectors and contemporary ecology: testing dispersal in a locally distributed cycad, Macrozamia lucida (Cycadales)

E. L. Snow A B and G. H. Walter A
+ Author Affiliations
- Author Affiliations

A School of Integrative Biology, The University of Queensland, Brisbane, Qld 4072, Australia.

B Corresponding author. Email: lizsnow@optusnet.com.au

Australian Journal of Botany 55(6) 592-600 https://doi.org/10.1071/BT07009
Submitted: 24 May 2005  Accepted: 8 February 2007   Published: 27 September 2007

Abstract

The possible reasons for the localised distribution of Macrozamia lucida Johnson in south-eastern Queensland were investigated through testing and quantifying aspects of seed dispersal, ex situ germination across local substrates and the spatial distribution of plants of different ages. Seeds of cones exposed to animals were moved significantly further (108.4 ± 13 cm, n = 10 cones) than those of cones not exposed to animals (49 ± 11 cm, n = 4). Only two mammal species interacted with seeds, common brushtail possums (Trichosurus vulpecula) and bush rats (Rattus fuscipes), but relatively infrequently. The possums were both seed dispersers and predators, whereas the rats ate only sarcotesta. Seed predation and removal occurred at a constant but low rate at cones exposed to animals, compared with no seed removal at unexposed cones. Seeds with sarcotesta intact and sarcotesta alone suffered significantly higher rates of removal by mammals. Seeds in soil had a significantly higher rate of germination (50%) than those in gravel (24.4%) or leaf litter (25.6%) and partially buried seeds germinated at a significantly higher rate (51.2%) than those on the surface (23.2%) and those buried completely (25.6%). In summary, this population appears to be localised spatially by low rates of dispersal, restricted dispersal distance and limited sites for successful germination. The results are discussed in relation to the possible extinction of the original seed dispersers of these organisms and the limitations this imposes on these plants should they be exposed to an unfavourable climatic regime.


Acknowledgements

We acknowledge Peter Machin and Grus Farley for their assistance in the field, and to Irene Terry and Bob Roemer for their encouragement and helpful comments on the manuscript. Thanks go to Nazim Khan, Graeme Hastwell and Raghu for their helpful advice regarding statistical methods and analysis. Jack Butler of Queensland Seed Testing Laboratories and Gerd Dowideit from The University of Queensland School of Geography generously assisted in assessing seed viability and surveying the cycad population, respectively. Queensland Parks and Wildlife kindly permitted seed collection (permit number WISP00705702) and Brisbane Forest Park likewise allowed scientific work at the study site. Assistance was also provided by The University of Queensland through ethics permit number ZOO/ENT/170/02/H.


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