Do phylogenetic community metrics reveal the South African quartz fields as terrestrial-habitat islands?

Daniel A Zhigila; Tammy L Elliott; Ute Schmiedel; A Muthama Muasya

doi:10.1093/aob/mcae027

Do phylogenetic community metrics reveal the South African quartz fields as terrestrial-habitat islands?

Ann Bot. 2024 Feb 24:mcae027. doi: 10.1093/aob/mcae027. Online ahead of print.

Authors

Daniel A Zhigila^{1

2

3}, Tammy L Elliott², Ute Schmiedel⁴, A Muthama Muasya²

Affiliations

¹ Department of Botany, Gombe State University, PMB 127, Tudun Wada, Gombe, Gombe State, Nigeria.
² Bolus Herbarium, Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch, Cape Town 7701, South Africa.
³ Department of Organismic and Evolutionary Biology, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA 02138, USA.
⁴ Organismic Botany and Mycology, Institute of Plant Science and Microbiology, University of Hamburg, Germany.

PMID: 38401154
DOI: 10.1093/aob/mcae027

Abstract

Background and aims: The quartz fields of the Greater Cape Floristic Region (GCFR) are arid and island-like special habitats, hosting about 142 habitat-specialized plant species of which 81% are local endemics, characterized by a rapid turnover of species between and among sites. We use several phylogenetic community metrics to i) examine species diversity and phylogenetic structure within and among quartz fields; ii) investigate whether quartz field specialists are evolutionarily drawn from local species pools, while the alternative hypothesis posits that there is no significant evolutionary connection between quartz field specialists and the local species pools; and iii) determine whether there is an association between certain traits and the presence of species in quartz fields.

Methods: We sampled and developed dated phylogenies for six species-rich angiosperm families (Aizoaceae, Asteraceae, Crassulaceae, Cyperaceae, Fabaceae and Santalaceae) represented in the quartz field floras of southern Africa. Specifically, we focused on the flora of three quartz field regions in South Africa (Knersvlakte, Little Karoo and Overberg) and their surrounding species pools to address our research questions, scoring traits associated with harsh environments.

Key results: We found that the Overberg and Little Karoo had the highest level of species overlap for families Aizoaceae and Fabaceae, while the Knersvlakte and the Overberg had the highest species overlap for families Asteraceae, Crassulaceae, and Santalaceae. Although our phylogenetic community structure and trait analyses showed no clear patterns, relatively low pairwise phylogenetic distances between specialists and their local species pools for Aizoaceae and Fabaceae suggest that quartz species could be evolutionarily drawn from their surrounding areas, with phylogenetic overdispersion in Knersvlakte and Little Karoo for Aizoaceae and Crassulaceae.

Conclusions: Despite their proximity to one another within the GCFR, the studied areas differ in their species pools and the phylogenetic structure of their specialists. Our work provides further justification for increased conservation focus of these unique habitats under future scenarios of global change.

Keywords: Aizoaceae; Asteraceae; Crassulaceae; Cyperaceae; Fabaceae; Santalaceae; community phylogenetics; phylogenetic diversity; specialized taxa.