Size class, sex ratio, and spatial distribution of four populations of Pimelea microcephala subsp. microcephala under different long-term rainfall regimes

Abstract

The separation of sexes in dioecious plants enables males and females to adopt different strategies to balance reproduction and growth, but can also lead to female susceptibility due to their high reproductive burden. Understanding if a dioecious species is susceptible or adaptable in the face of worsening abiotic conditions would be useful for revegetating habitats under climate change. Our study compared four populations of the Australian native shrub, Pimelea microcephala subsp. microcephala (n = 885) across an annual rainfall gradient of ∼250–400 mm to understand the impact of decreasing rainfall on size classes, growth metrics, sex ratio, the proportion of juveniles and spatial distributions. We found that irrespective of site rainfall, male and female plants achieved similar sizes. The populations exhibited four size classes, defined by height, diameter and sex, but not site rainfall (unpaired group method with arithmetic mean cluster analysis, p < .05). Spatially, populations reflected the clumped distribution of overlying canopy cover, and did not demonstrate niche partitioning between sexes. The lack of population variation with rainfall indicates that the species may be suitable for arid zone revegetation in arid regions with declining rainfall. Conservation management of the species should include maintaining canopy tree cover to encourage seed dispersal.

Keywords:

• Australia
• dioecy
• environmental gradient
• size classing

Acknowledgments

The authors would also like to thank the owners of the property ‘Baron’ for their support of the project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors are grateful to the Ecological Society of Australia (Grant Round 2, 2020), the Royal Society of South Australia (Grant Round 2020) and Nature Foundation Inc. (Grant No. 2020-13) for financially supporting this research. J.T. Draper was supported by an Australian Government Research Training Program Scholarship at the time of research.