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van der Merwe S, Greve M, Skowno AL, Hoffman MT, Cramer MD. Can vegetation be discretely classified in species-poor environments? Testing plant community concepts for vegetation monitoring on sub-Antarctic Marion Island. Ecol Evol 2023; 13:e9681. [PMID: 36620413 PMCID: PMC9811060 DOI: 10.1002/ece3.9681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 11/08/2022] [Accepted: 12/08/2022] [Indexed: 01/05/2023] Open
Abstract
The updating and rethinking of vegetation classifications is important for ecosystem monitoring in a rapidly changing world, where the distribution of vegetation is changing. The general assumption that discrete and persistent plant communities exist that can be monitored efficiently, is rarely tested before undertaking a classification. Marion Island (MI) is comprised of species-poor vegetation undergoing rapid environmental change. It presents a unique opportunity to test the ability to discretely classify species-poor vegetation with recently developed objective classification techniques and relate it to previous classifications. We classified vascular species data of 476 plots sampled across MI, using Ward hierarchical clustering, divisive analysis clustering, non-hierarchical kmeans and partitioning around medoids. Internal cluster validation was performed using silhouette widths, Dunn index, connectivity of clusters and gap statistic. Indicator species analyses were also conducted on the best performing clustering methods. We evaluated the outputs against previously classified units. Ward clustering performed the best, with the highest average silhouette width and Dunn index, as well as the lowest connectivity. The number of clusters differed amongst the clustering methods, but most validation measures, including for Ward clustering, indicated that two and three clusters are the best fit for the data. However, all classification methods produced weakly separated, highly connected clusters with low compactness and low fidelity and specificity to clusters. There was no particularly robust and effective classification outcome that could group plots into previously suggested vegetation units based on species composition alone. The relatively recent age (c. 450,000 years B.P.), glaciation history (last glacial maximum 34,500 years B.P.) and isolation of the sub-Antarctic islands may have hindered the development of strong vascular plant species assemblages with discrete boundaries. Discrete classification at the community-level using species composition may not be suitable in such species-poor environments. Species-level, rather than community-level, monitoring may thus be more appropriate in species-poor environments, aligning with continuum theory rather than community theory.
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Affiliation(s)
- Stephni van der Merwe
- Department of Biological SciencesUniversity of Cape TownCape TownSouth Africa,Kirstenbosch Research CentreSouth African National Biodiversity InstituteCape TownSouth Africa
| | - Michelle Greve
- Department of Plant and Soil SciencesUniversity of PretoriaPretoriaSouth Africa
| | - Andrew Luke Skowno
- Department of Biological SciencesUniversity of Cape TownCape TownSouth Africa,Kirstenbosch Research CentreSouth African National Biodiversity InstituteCape TownSouth Africa
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Cramer MD, Hedding DW, Greve M, Midgley GF, Ripley BS. Plant specialisation may limit climate‐induced vegetation change to within topographic and edaphic niches on a
sub‐Antarctic
island. Funct Ecol 2022. [DOI: 10.1111/1365-2435.14123] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Michael D. Cramer
- Department of Biological Sciences University of Cape Town Cape Town South Africa
| | - David W. Hedding
- Department of Geography University of South Africa Florida South Africa
| | - Michelle Greve
- Department of Plant and Soil Sciences University of Pretoria South Africa
| | - Guy F. Midgley
- Department of Botany and Zoology University of Stellenbosch Stellenbosch South Africa
| | - Brad S. Ripley
- Department of Botany Rhodes University Grahamstown South Africa
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Mairal M, Chown SL, Shaw J, Chala D, Chau JH, Hui C, Kalwij JM, Münzbergová Z, Jansen van Vuuren B, Le Roux JJ. Human activity strongly influences genetic dynamics of the most widespread invasive plant in the sub-Antarctic. Mol Ecol 2021; 31:1649-1665. [PMID: 34181792 DOI: 10.1111/mec.16045] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 06/14/2021] [Accepted: 06/21/2021] [Indexed: 11/26/2022]
Abstract
The link between the successful establishment of alien species and propagule pressure is well-documented. Less known is how humans influence the post-introduction dynamics of invasive alien populations. The latter requires studying parallel invasions by the same species in habitats that are differently impacted by humans. We analysed microsatellite and genome size variation, and then compared the genetic diversity and structure of invasive Poa annua L. on two sub-Antarctic islands: human-occupied Marion Island and unoccupied Prince Edward Island. We also carried out niche modelling to map the potential distribution of the species on both islands. We found high levels of genetic diversity and evidence for extensive admixture between genetically distinct lineages of P. annua on Marion Island. By contrast, the Prince Edward Island populations showed low genetic diversity, no apparent admixture, and had smaller genomes. On both islands, high genetic diversity was apparent at human landing sites, and on Marion Island, also around human settlements, suggesting that these areas received multiple introductions and/or acted as initial introduction sites and secondary sources (bridgeheads) for invasive populations. More than 70 years of continuous human activity associated with a meteorological station on Marion Island led to a distribution of this species around human settlements and along footpaths, which facilitates ongoing gene flow among geographically separated populations. By contrast, this was not the case for Prince Edward Island, where P. annua populations showed high genetic structure. The high levels of genetic variation and admixture in P. annua facilitated by human activity, coupled with high habitat suitability on both islands, suggest that P. annua is likely to increase its distribution and abundance in the future.
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Affiliation(s)
- Mario Mairal
- Department of Botany and Zoology, Stellenbosch University, Stellenbosch, South Africa.,Departamento de Biodiversidad, Ecología y Evolución, Facultad de Ciencias Biológicas, Universidad Complutense de Madrid, Ciudad Universitaria, Madrid, Spain
| | - Steven L Chown
- Securing Antarctica's Environmental Future, School of Biological Sciences, Monash University, Victoria, Australia
| | - Justine Shaw
- School of Biological Sciences, The University of Queensland, St Lucia, Queensland, Australia
| | - Desalegn Chala
- Natural History Museum, University of Oslo, Oslo, Norway
| | - John H Chau
- Centre for Ecological Genomics and Wildlife Conservation, Department of Zoology, University of Johannesburg, Auckland Park, South Africa
| | - Cang Hui
- Centre for Invasion Biology, Department of Mathematical Sciences, Stellenbosch University, Stellenbosch, South Africa.,Biodiversity Informatics Unit, African Institute for Mathematical Sciences, Cape Town, South Africa
| | - Jesse M Kalwij
- Centre for Ecological Genomics and Wildlife Conservation, Department of Zoology, University of Johannesburg, Auckland Park, South Africa.,Institute of Geography and Geoecology, Karlsruhe Institute of Technology, Karlsruhe, Germany
| | - Zuzana Münzbergová
- Department of Botany, Charles University, Prague, Czech Republic.,Department of Population Ecology, Czech Academy of Science, Průhonice, Czech Republic
| | - Bettine Jansen van Vuuren
- Centre for Ecological Genomics and Wildlife Conservation, Department of Zoology, University of Johannesburg, Auckland Park, South Africa
| | - Johannes J Le Roux
- Department of Botany and Zoology, Stellenbosch University, Stellenbosch, South Africa.,Department of Biological Sciences, Macquarie University, Sydney, New South Wales, Australia
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