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The population structure and dynamics of Macrozamia riedlei within the Perth region

Gerlach, Mark (2012) The population structure and dynamics of Macrozamia riedlei within the Perth region. Honours thesis, Murdoch University.

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Macrozamia riedlei is a long lived, large seeded member of the cycad family, common to the Jarrah forest and Banksia woodlands within the Perth region of Western Australia. Because of the large size of the seeds (up to 50mm), it is believed that large bodied herbivores are required to act as dispersal agents. Currently, the Emu (Dromaius novaehollandiae) is considered to be the primary dispersal agent for M. riedlei. Due to anthropogenic activities, much of the habitat of M.riedlei is becoming fragmented primarily through agricultural and residential land clearing. This leads to the potential restriction of long distance dispersal of seed, required for healthy gene flow and the ability for range expansion in the face of an uncertain climatic future.

The aims of this study were to investigate the current population structure of M. riedlei at three locations within the Perth region and to identify dispersal agents and the distance they can disperse seeds. The sites chosen were Avon Valley, Sawyers Valley and Kings Park; these three sites were chosen since they present a gradient in emu population density, from abundant at Avon Valley to absent for a century at Kings Park.

To ascertain how these three populations of M. riedlei were currently structured, all plants in replicate 50x50m plots were recorded at each site and the data used to analyse the demographic and spatial structure of each population. Because of the gradient in emu population density, it was hypothesised that the spatial and demographic structure would differ at each site, due to the availability of emus to disperse the seeds of M. riedlei. The three study sites were shown to be very similar in population structure despite the difference in emu numbers. It was also found that the Australia Raven (Corvis coronoides) was capable of dispersing the seeds of M. riedlei over distances of up to 390m, indicating that ravens are able to act as suitable dispersers of M.riedlei seeds and in the absence of emus maybe considered as a key dispersal agent.

Publication Type: Thesis (Honours)
Murdoch Affiliation: School of Environmental Science
Supervisor: Ladd, Phil and Enright, Neal
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