DOI: 10.5061/dryad.4f4qrfjbw
title: Plant diversity across small-scale boundaries

description: Questions: Habitat islands are often characterized by the presence of more
 or less sharp boundaries to adjacent matrix habitats. However, knowledge
 on boundaries of natural habitat islands is scarce, especially regarding
 patterns of beta diversity and its two underlying components: species
 turnover and nestedness. We therefore aim to quantify the effects of
 fine-scaled and sharp boundaries of quartz islands (quartz-gravel covered
 soils) on the different components of plant beta diversity and how they
 are linked to different soil environmental drivers. Location: Knersvlakte,
 Western Cape, South Africa. Methods: We sampled plant species richness in
 56 fine-scale transects of 6 × 1 m² plots across eight different boundary
 types (four quartz island – matrix, four between habitats on quartz
 islands). Soil depth and chemistry (pH, electrical conductivity) were
 analyzed for each 1 m² plot. Differences in the two beta
 diversity components (turnover and nestedness) for each boundary type were
 tested by t-tests. We used linear models to test relationships between
 species and environmental dissimilarity. Results: All boundary types
 showed high beta diversity. Species turnover was the prevailing component
 for six boundary types, the nestedness component was only important for
 two boundary types. We found a significant linear increase of species
 dissimilarity with increasing dissimilarity in soil pH and distinct plant
 communities for the habitat types, but no significant increase for
 electrical conductivity or soil depth. Conclusions: The spatial
 distinctiveness of the quartz islands leads to sharp boundaries, which
 result in high beta diversity, mainly through species turnover. This
 reflects the high levels of diversification and adaptation of the local
 plant communities. Nestedness occurred at two boundaries to the matrix,
 indicating that the latter does not necessarily represent an impermeable
 boundary for all species of the respective ecosystem. Studying diversity
 patterns across boundaries contributes to the question of applicability of
 island biogeography theory to habitat islands.
description: Eibes_etal_JVS_RA_05693_environmental data:
 ID: Plot ID, combining "transect_no",
 "boundary_type" and "transect_quadrat" of the
 respective 1m² plot transect_no: Transect number, 56
 transects in total electrical_conductivity: Electrical
 conductivity of mixed soil sample per quadrat (mS/cm)
 pH: soil pH of mixed soil sample per quadrat
 soil depth: mean soil depth per quadrat (in cm) transect_quadrat:
 Position of 1m² plot (=quadrat) along the transect (see schematic
 figure) boundary_type: The boundary/transition type, in
 total 8 different types, see habitat legend habitat_A:
 Habitat type of site A of the respective transect
 habitat_B: Habitat type of site B of the respective
 transect habitat: Habitat type of the quadrat, 6
 different habitat types FS Argyroderma fissum -
 Cephalophyllum spissum (quartz habitat) D Dicrocaulon
 brevifolium (quartz habitat) R Ruschia burtoniae
 (quartz habitat) S Salt pan (quartz habitat)
 NQF Non-quartz field (matrix habitat) H
 Heuweltjies (matrix habitat)
 Eibes_etal_JVS_RA_05693_vegetation data: ID: Plot ID, combining
 "transect_no", "boundary_type" and
 "transect_quadrat" of the respective 1m² plot
 Rownames: Scientific (or preliminary) species names of the 101
 present plant species