Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments
Thesis (PhD)--Stellenbosch University, 2023.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Stellenbosch : Stellenbosch University
2023
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613875026788352 |
|---|---|
| access_status_str | Open Access |
| author | Ncube, Thinabakho R.L |
| author2 | De Klerk, Helen |
| author_browse | De Klerk, Helen Ncube, Thinabakho R.L |
| author_facet | De Klerk, Helen Ncube, Thinabakho R.L |
| author_sort | Ncube, Thinabakho R.L |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2023. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/129389 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:43:05.531Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/129389 Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments Ncube, Thinabakho R.L De Klerk, Helen Hui, Cang Lovett, Jon C Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies. Ecotone; biome boundary; fractal dimension; spatial analytics; generalised dissimilarity modelling; beta diversity; zeta diversity; multi-site generalised dissimilarity modelling; species richness; compositional turnover; bioregionalisation; biogeography; macroecology; biodiversity hotspots; African conservation; climate change; biome shifts. Thesis (PhD)--Stellenbosch University, 2023. Ecotones are transition zones of plant species compositional turnover. They possess inherent fractal characteristics corresponding to the shape of boundary lines between adjacent compositional clusters of plant assemblages. In recent decades, their environmental configurations have been defined, detected, and explained following field observations, experiments, and modelling approaches. However, the spatial characteristics and determinants of ecotones have rarely been explored explicitly for compositional clusters, likely due to methodological and data limitations. Consequently, the aim of this research was to spatially characterise ecotones at present-day and future environments in mainland sub-Saharan Africa. Using a model-based distribution dataset of more than 23,000 African vascular plant species (of 3616 genera), this dissertation addressed three central questions pertaining to the biogeographical patterns and drivers of African vascular plants, the fractal dimension of ecotones at present-day, and the wax and wane of (existing and novel) biomes and ecotones in future climates. First, at 20km resolution species richness was estimated as species counts at site-level and explained using a generalised additive modelling (GAM) approach. Compositional turnover was mapped according to the nonmetric multidimensional scaling (nMDS) of between-site Jaccard dissimilarity, with compositional turnover of narrow-ranged vs widespread species explained using a multi-site generalised dissimilarity modelling (MS-GDM) of zeta diversity approach. Results showed species-rich pockets, with the MDS performing reasonably well (stress = 0.057) revealed gradients of compositional clusters of African vascular plants across the study extent. Climate was the major driver of species richness and mean annual precipitation exerted the strongest response to the richness variation. Compositional turnover of narrow-ranged and widespread species was largely driven by environmental heterogeneity, respectively. In both cases, the compositions were subjected to strong differential responses to geographic distance and soil pH. Second, based on the pattern of species compositional turnover, compositional clusters were delineated by determining the optimal number of clusters using K-means and Clustering Large Applications (CLARA) algorithms, with the clustering validity evaluated on the premise of a silhouette coefficient. The present-day ecotones were then extracted as boundary lines between adjacent compositional clusters, and their spatial structures measured by the box-counting fractal dimension (FD). The variation of ecotone FDs and a suite of ecologically relevant environmental factors was explained by the GAMs. CLARA succeeded in partitioning seven compositional clusters (0.49 silhouette coefficient), from which 11 ecotones were identified, with seven characterised as true fractals (exceeding topological dimension) but having a low fractal dimension. The spatial structure of the present-day ecotones was mainly encapsulated by gradients of soil texture and structure, and less by latitudes, thus leading to the compositional turnover of the African vascular plants at present-day. Third, the model-based distributional data was predicted as a Jaccard dissimilarity between plant assemblages in mainland sub-Saharan Africa at present-day and in 2050 and 2070 under shared socioeconomic pathways (SSPs) 126 and 585 using a generalised dissimilarity modelling (GDM) approach. The optimal number of clusters was determined using K-means and CLARA algorithms, with the clustering validity also evaluated using a silhouette coefficient. Ecotones in future climates were extracted as boundary lines between adjacent biomes that represent clusters of compositional dissimilarity, and their spatial structures characterised by the FD. GAMs were then employed to explore the relationships between the ecotones and the future climates. In both future epochs, key trends in biome shifts (CLARA: silhouette coefficient = 0.52) revealed varied latitudinal expansions and contractions, and in some cases prompted compositional mismatches. Novel compositional assemblages were found and became prominent in the late century. At the ecotones, spatial structures whose fractal dimensions exceeded their topological dimensions, were shown to be potentially configured by different climatic bounds, leading to the species compositional turnover of the African vascular plants in future climates. Overall, insight from these studies can aid conservationists to better conserve biodiversity of African vascular plants. Doctoral 2023-11-15T09:11:41Z 2024-02-20T09:50:58Z 2023-11-15T09:11:41Z 2024-02-20T09:50:58Z 2023-12 Thesis https://scholar.sun.ac.za/handle/10019.1/129389 en Stellenbosch University 300 pages : ill. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Ecotone; biome boundary; fractal dimension; spatial analytics; generalised dissimilarity modelling; beta diversity; zeta diversity; multi-site generalised dissimilarity modelling; species richness; compositional turnover; bioregionalisation; biogeography; macroecology; biodiversity hotspots; African conservation; climate change; biome shifts. Ncube, Thinabakho R.L Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments |
| title | Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments |
| title_full | Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments |
| title_fullStr | Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments |
| title_full_unstemmed | Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments |
| title_short | Modelling the clusters and boundaries of sub-Saharan plant assemblages in future environments |
| title_sort | modelling the clusters and boundaries of sub saharan plant assemblages in future environments |
| topic | Ecotone; biome boundary; fractal dimension; spatial analytics; generalised dissimilarity modelling; beta diversity; zeta diversity; multi-site generalised dissimilarity modelling; species richness; compositional turnover; bioregionalisation; biogeography; macroecology; biodiversity hotspots; African conservation; climate change; biome shifts. |
| url | https://scholar.sun.ac.za/handle/10019.1/129389 |
| work_keys_str_mv | AT ncubethinabakhorl modellingtheclustersandboundariesofsubsaharanplantassemblagesinfutureenvironments |