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The global latitudinal diversity gradient pattern in spiders

Piel, William H.
Journal of biogeography 2018 v.45 no.8 pp. 1896-1904
Araneae, data collection, species diversity
AIM: The aim of this study was to test the hypothesis that the global latitudinal diversity gradient pattern in spiders is pear‐shaped, with maximum species diversity shifted south of the Equator, rather than egg‐shaped, centred on the equator, this study infers the gradient using two large datasets. LOCATION: Global terrestrial. TIME PERIOD: Data sources range from 1757–2017; data assembled April 2017. TAXON: Spiders (Araneae). METHODS: Using metadata on the countries of origin for 98% of all described spider species, this study applies PostGIS queries to calculate the number of species, and the species richness per land area, along ten‐degree latitudinal bands. RESULTS: More spider species are known in the Northern Hemisphere than in the Southern Hemisphere. Although the global latitudinal diversity gradient pattern in species richness per area is, indeed, pear‐shaped, this pattern only applies to Old World longitudes and only if it is assumed that the species‐area relationship is linear. Without this assumption, the latitudinal gradient matches the classic parabolic shape. MAIN CONCLUSIONS: Using data from the World Spider Catalog, the global latitudinal diversity gradient pattern for spiders, in terms of species per unit area and assuming a power function for the species‐area relationship, is egg‐shaped, or parabolic, rather than pear‐shaped as previously claimed.