The spatial pattern of plant biodiversity in the greater cape floristic region of South Africa: comparing distribution models with expert range maps
Abstract
The Greater Cape Floristic Region (GCFR) of South Africa is well known for its plant biodiversity – it contains nearly 20% of Africa’s plant species in less than 0.5% of Africa’s total area. But, little is known about the spatial pattern of this biodiversity. This research compares the spatial patterns of biodiversity in the GCFR derived from species distribution models (SDMs) and expert range maps. Focusing on plant species from the Restionacea family, spatial patterns of species biodiversity from expert range maps and SDM predictions were mapped at 1km resolution. Spatial patterns derived from the expert range maps vary smoothly, capturing the general characteristics, in contrast, the patterns derived from SDM predictions capture fine-grain variability of the biodiversity hotspot. In beta diversity, lines are highlighted at the boundaries of species ranges because the coarse grain of the expert maps isolates the range boundaries, while from the SDM-derived ranges, areas with high beta value are distributed primarily along the mountain ridges. This study reveals the difference between spatial patterns of biodiversity from expert range maps and species distribution modelling, which implies a possibility to combine these two methods in the future to help researchers identify the priority areas when the conservation resource and financial investment are limited.
Keywords: Species biodiversity, Spatial Pattern, South Africa
Conceptual Diagram
Introduction
AND
The Greater Cape Floristic Region (GCFR) in South Africa has some of the world’s richest plant biodiversity and contains two global biodiversity hotspots: Succulent Karoo and Fynbos (Goldblatt and Manning 2002).
Although the total area is around 90,000 km2, less than 5% of the African subcontinent and 7% of South Africa, the region contains 44% of the plant species found in Southern Africa (Arnold and De Wet 1993).
Expert range maps are drawn by groups of experts based on the association of expert knowledge and experience.
The major use of the expert range maps is to design protected areas for species conservation and evaluate the species richness (Hurlbert and White 2005a).
Species distribution models (SDMs), also commonly referred as Ecological Niche Models, are one of the significant tools to predict the environmental suitability of species occurrence in space and time (Guisan et al. 2013).
Alpha and beta diversity are two indices used to evaluate biodiversity: Alpha diversity, also known as species richness, is always calculated as the total number of species in an area; Beta diversity is defined by species compositional change among sites in the geographic area of interest (Legendre, Borcard, and Peres-Neto 2005).
BUT
But, the spatial pattern of plant species biodiversity derived from expert range maps and species distribution modelling in GCFR has not been systematically compared.
THEREFORE
Therefore, comparing the spatial pattern of plant species biodiversity from expert range maps and SDMs could promote the understanding of the species compositional change in GCFR areas.
The common results of these two different methods in areas with high biodiversity can help researchers determine priority areas when the conservation resource and financial investment are limited.
Method
The investigation involved processing the expert range maps and species presence-only data with environmental factors to determine species distribution and calculate species biodiversity. Plant species data includes expert range maps data and presence-only data. The expert range maps of different species were analysed by the moving window to obtain the spatial pattern of species richness and beta diversity in 0.01 degrees. In addition, the species presence-only data was combined with various environmental layers (elevation, annual mean precipitation/temperature, precipitation/temperature seasonality, topographic position index) to build different species distributions with the maxent algorithm analysis in 1km resolution. After that, the 10th percentile threshold was selected in SDM predictions to obtain the spatial patterns of species richness and beta diversity.
Results
From the spatial pattern of species richness derived from the expert range maps, and species distribution modelling, the highest values of species richness were mainly distributed on the southern-west Cape Floristic Region (CFR) with discontinuous patches and along with the mountain ranges that run from east to west, and south to north.
The beta diversity map derived from expert range maps showed two major areas with high beta diversity: western CFR and southeastern CFR.
In the beta diversity map derived from SDMs, the areas with relatively high beta diversity were mainly distributed in northern-west CFR and northern-east CFR.
The plant species richness derived from the expert range maps varied smoothly, catching the general characteristics of the distributions on a large scale, even though the local information is unknown.
Compared with maps of species richness and beta diversity derived from expert range maps, the maps derived from SDMs’ displayed more acceptable patterns in areas with high richness and high beta diversity, which reflect topographical features, such as the distribution of mountain ridges.
However, the expert range maps highlight multiple irregular lines in areas with high beta diversity along range boundaries of various species with a dispersed distribution.
Annual precipitation and annual mean temperature explained the most variance in the spatial pattern of species richness.
Poster
