Patchy distribution and varied habitats of Macrozamia lucida cycads explained by constancy in a key environmental variable

• Published in: Australian journal of botany Vol. 64; no. 4; pp. 285 - 294
• Main Authors: Kaye, L. A, G. H. Walter, S. Raghu
• Format: Journal Article
• Language: English
• Published: CSIRO Publishing 01.01.2016
• Subjects: adults; biogeography; correlation; ecosystems; environmental factors; environmental heterogeneity; habitats; leaves; Macrozamia; relative humidity; reproductive performance; resource limitation; restricted distribution; spatial distribution; surveys; Queensland
• ISSN: 0067-1924; 1444-9862
• DOI: 10.1071/BT15244

Identifying the influence of environmental variables on the spatio-temporal distribution of organisms remains a central goal of ecology. Although environmental limits to the geographic range of species have been investigated, less information is available regarding the influence of environmental variables limiting species to discrete patches within their geographic range. Identifying environmental variables of importance to the species in question is further complicated where the patches appear to be distributed across a variety of outwardly dissimilar habitats. We assessed the influence of environmental variables on the patchy distribution of Macrozamia lucida L.A.S. Johnson (Zamiaceae) cycads endemic to south-east Queensland, Australia. Here we show that patches of M. lucida are consistently associated with elevated moisture, despite the patches being located in contrasting habitats and topographic positions. Our survey results across five field sites demonstrate that both cycad abundance and adult cycad condition (estimated from measures of adult cycad leaf production and reproductive output) are positively correlated with elevated moisture, as measured by mean minimum relative humidity at the plant–soil interface. The historical biogeography of the genus Macrozamia may be intimately linked with the contraction and fragmentation of Australia’s mesic biomes during the Miocene. It is plausible that current distribution pattern of M. lucida, restricted to discrete patches that meet the species’ environmental requirements, reflects a contraction and fragmentation within its range from a more regular historical distribution under more favourable climatic regimes.