Showing papers by "Holger Kreft published in 2007"

Global patterns and determinants of vascular plant diversity

Abstract: Plants, with an estimated 300,000 species, provide crucial primary production and ecosystem structure. To date, our quantitative understanding of diversity gradients of megadiverse clades such as plants has been hampered by the paucity of distribution data. Here, we investigate the global-scale species-richness pattern of vascular plants and examine its environmental and potential his- torical determinants. Across 1,032 geographic regions worldwide, potential evapotranspiration, the number of wet days per year, and measurements of topographical and habitat heterogeneity emerge as core predictors of species richness. After accounting for environmental effects, the residual differences across the major floristic kingdoms are minor, with the exception of the uniquely diverse Cape Region, highlighting the important role of historical contingencies. Notably, the South African Cape region contains more than twice as many species as expected by the global environmental model, confirming its uniquely evolved flora. A combined multipredictor model explains 70% of the global variation in species richness and fully accounts for the enigmatic latitudinal gradient in species richness. The models illustrate the geographic interplay of different environmental predictors of species richness. Our findings highlight that different hypotheses about the causes of diversity gradients are not mutually exclusive, but likely act synergistically with water- energy dynamics playing a dominant role. The presented geostatistical approach is likely to prove instrumental for identifying richness patterns of the many other taxa without single-species distribution data that still escape our understanding. biodiversity historical contingency latitudinal gradient macroecology species richness

Global diversity of island floras from a macroecological perspective

Abstract: Islands harbour a significant portion of all plant species worldwide. Their biota are often characterized by narrow distributions and are particularly susceptible to biological invasions and climate change. To date, the global richness pattern of islands is only poorly documented and factors causing differences in species numbers remain controversial. Here, we present the first global analysis of 488 island and 970 mainland floras. We test the relationship between island characteristics (area, isolation, topography, climate and geology) and species richness using traditional and spatial models. Area is the strongest determinant of island species numbers (R(2) = 0.66) but a weaker predictor for mainlands (R(2) = 0.25). Multivariate analyses reveal that all investigated variables significantly contribute to insular species richness with area being the strongest followed by isolation, temperature and precipitation with about equally strong effects. Elevation and island geology show relatively weak yet significant effects. Together these variables account for 85% of the global variation in species richness.

Indicator value of different vascular plant families for overall plant diversity in the savanna belt of western africa (abridged title: grasses as indicators of plant diversity)

Abstract: Detailed plant diversity information is lacking for Africa, as for many other regions in the tropics, therefore we have used our collection and observation databases to search for possible indicator groups. Digitization of specimen label data for Burkina Faso from the Herbarium Senckenbergianum (FR) and the Ouagadougou University Herbarium (OUA) led to a database containing 18 000 specimens. Field observations from about 3700 releves (Braun-Blanquet method, BIOTA standard releves, simple inventories) were added to the database and together used to model potential species distributions for Burkina Faso on a ten-minute grid. Genetic Algorithm for Rule-set Production (GARP) was used with temperature, precipitation, humidity, and elevation data. Based on these modeled distributions, overall vascular plant diversity was correlated to the diversities of the ten commonest families (Poaceae, Fabaceae, Cyperaceae, Rubiaceae, Combretaceae, Euphorbiaceae, Mimosaceae, Asteraceae, Caesalpiniaceae, Malvaceae). Poaceae and Fabaceae turned out to be the most suitable taxa. The value of these families as indicators for assessing biodiversity is discussed. The results are compared to similar analyses based on releves only. Accepted 2 August 2007.