DOI: 10.5061/dryad.b2rbnzsnw
title: Data from: Specific island biogeographic and landscape features shape plant diversity and habitat specialism on edaphic quartz islands in an arid ocean

description: Aim: Habitat islands on special soils in arid regions offer unique
 environmental conditions for plants and often harbour specialized and
 endemic floras, thus having high nature conservation value. In addition,
 habitat islands are characterized by distinct spatial features such as
 island characteristics, habitat diversity, insularity, and matrix effects.
 However, their role as drivers of biodiversity on habitat islands is still
 unclear. Therefore, we aim to quantify the extent to which island
 parameters, insularity metrics, habitat diversity, and the surrounding
 matrix, explain plant diversity on edaphic quartz islands. Location: The
 quartz islands in our study area, located in the Knersvlakte Nature
 Reserve (South Africa), consist of naturally isolated patches covered by
 white quartz gravel within a zonal semi-arid vegetation matrix, hosting a
 unique vegetation predominantly composed of dwarf succulent shrubs.
 Methods: We conducted a comprehensive field survey of the perennial flora
 on 47 quartz islands, calculating species richness, habitat specialist
 richness, endemic richness, and the percentage of endemics and habitat
 specialists. We used spatial island characteristics derived from satellite
 imagery to analyse the data. Results: Our findings indicate that island
 area and habitat diversity are the most reliable predictors of species
 richness, as well as the richness of endemics and habitat specialists per
 island. Including measures of matrix contrast and area-based isolation
 improved the predictive power of several models, particularly those
 involving percentage endemism. However, distance-based isolation measures
 had little to no explanatory value in relation to the observed variance.
 Main Conclusions: The diversity of quartz islands can be effectively
 described using specific island biogeographic parameters such as the
 island area or the habitat diversity. However, measuring isolation in
 edaphic island systems may require alternative quantification methods,
 such as incorporating matrix properties. This study contributes to the
 question whether island biogeographical theories can be applied to
 natural, edaphically unique habitat islands.
description: # Data from: Specific island biogeographic and landscape features shape
 plant diversity and habitat specialism on edaphic quartz islands in an
 arid ocean
 [https://doi.org/10.1038/s41598-025-94562-5](https://doi.org/10.1038/s41598-025-94562-5) This dataset contains the data on which the analyses and results published in the linked research article in Scientific Reports are based. Quartz islands are edaphic habitat islands located in the arid zone of the Succulent Karoo in southern Africa. These habitat islands harbour outstanding numbers of endemic and habitat specialised plant species. Therefore, they provide unique opportunities to apply the theory of island biogeography and to analyze which effect several spatial features of this habitat island archipelago have on the species richness and the richness of endemic plant species. Two additional files contain the supplementary information of the original article. These can be found in Supplemental Information on Zenodo (see Related Works) * Supplementary_Information_1 contains the Species List with Information on all species of this study. * Supplementary_Information_2 contains all additional tables and figures of the data analysis of the original article. ## Description of the data and file structure Data_ScientificReports_Island_biogeography_of_quartz_habitat_islands.xlsx The dataset contains information on 47 quartz islands (edaphic habitat islands) in Moedverloren, which is located in the Knersvlakte nature conservation are in South Africa (Western Cape). It contains 22 columns in which spatial and ecological parameters of these 47 islands are described. See the Explanation of the parameters and abbreviations in the table below: | Column | Explanation | | :------------------ | :----------------------------------------------------------- | | ISLAND\_ID | ID of the 47 islands | | spec\_rich | total species richness | | non\_QS | number of species that are not specialized on quartz | | quartz\_specialists | number of quartz habitat specialists | | KV | number of locally endemic species to the Knersvlakte | | KV\_perc | percentage of locally endemic species | | quartz\_spec\_perc | percentage of habitat specialists | | A | island area in m² | | P | island perimeter in m | | SHP | shape index (see Supplement) | | DNNI | distance to nearest neighbour island in m | | ANNI | area of nearest neighbour island in m² | | NI | neighbour index (see Supplement) | | DNSI | distance to nearest similarly large island in m | | DMI | distance to main island in m | | PX | proximity index (see Supplement) | | HABRICH | number of habitats on a quartz island (see Supplement) | | HABSHAN | Shannon-Wiener Index of HABRICH | | DI | diversity index according to Patton, 1975 (see Supplement) | | DNII\_47 | distance to nearest sampled island in m | | MC | matrix contrast (see Supplement) | | TE | target effect (see Supplement) |