Geographic patterns of vascular plant diversity at continental to global scales

Abstract

The studies presented in this paper analyse diversity patterns of land plants (mosses, ferns, gymnosperms, and angiosperms) at continental to global scales. A revised version of our earlier world map of vascular plant species richness and the first maps of species richness of mosses and gymnosperms on a global scale are presented. Diversity patterns of vascular plants are correlated with different measures of geodiversity (the diversity of the abiotic environment). Global centres of vascular plant diversity coincide with highly structured, geodiverse areas in the tropics and subtropics. These are the Chocó-Costa Rica region, the tropical eastern Andes and the north western Amazonia, the eastern Brazil, the northern Borneo, and New Guinea, as well as the South African Cape region, southern Mexico, East Himalaya, western Sumatra, Malaysia, and eastern Madagascar. Constraints imposed by the physical environment, such as the length of the thermal vegetation period or water availability, shape large scale trends of biodiversity. However, important centres of species richness and endemism can only be explained when taking into account the history of the floras. The main diversity centres in SE Asia are the same for gymnosperms as for all other vascular plants, but in other parts of the tropics and subtropics there is low gymnosperm diversity. The exceptions to this pattern are Mexico and California, which have almost as many species of gymnosperms as SE Asia. The increase in the number of species and genera published during the last 250 years is documented, based on data from the Index Kewensis. The first continental maps of Cactaceae diversity at species and genus level are used to show how choice of the taxonomic level affects the analysis and its implications for priority setting in biodiversity conservation. In this context, global biodiversity hotspots are discussed and an alternative world map of hotspots is proposed.

Global patterns and determinants of vascular plant diversity

“…4), and the predicted global map (Fig. 3b) confirms many regional trends and hotspots anticipated before (11,13,14,16,17,46). Geostatistical models (Fig.…”

“…We have shown that relatively few variables, namely a combination of high annual energy input with constant water supply and extraordinarily high spatiotopographic complexity, are able to accurately predict the location of global centers of plant richness (Costa Rica-Chocó, Tropical Eastern Andes, Atlantic Brazil, Northern Borneo, and New Guinea) (14,17). Astonishingly, the most species-rich grid cell according to our combined model (situated between Colombia and Ecuador; Fig.…”

“…46 for a full list of references). The data set was originally assembled to produce expert opinionbased global maps of plant species richness (11,14,17,19,46) and continental geostatistical (16,48,49) analyses. The original data set consists of Ͼ3,300 species-richness accounts referring to Ͼ1,800 geographic units.…”

“…Recently, considerable progress has been made toward documenting broad-scale patterns of plant richness (11,(14)(15)(16)(17)(18)(19)(20)(21). In general, two different data-type approaches are possible to map and analyze global richness gradients (22).…”

“…Our analysis is based on an exhaustive data set of 1,032 regions worldwide that has been used to produce expert opinion-based continental to global maps of plant species richness (11,14,17,21). We use both nonspatial and spatial (controlling for spatial autocorrelation) modeling techniques to test, in turn, the predictive potential of variables representing different hypotheses.…”