The global latitudinal diversity gradient pattern in spiders

Abstract

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.

A protocol for online documentation of spider biodiversity inventories applied to a Mexican tropical wet forest (Araneae, Araneomorphae)

“…Holarctic forests present the lowest richness with 115.24 +/-51.39 species, but the highest completeness values of 81.856% +/-8.72 (Cardoso et al 2008a, 2008b, Cardoso et al 2017bCoddington et al 1996;Scharff et al 2003). These values are also in agreement with recent analyses based on taxonomic data for spiders (Piel 2018 Footnote: Inventories marked with double dashes (--) did not mention the area sampled, or the area was delimited only for some of the sampling methods. Inventories marked with * did not make clear the sampled area, but one hectare was established by comparison with other studies from the same authors.…”

“…The completeness of these inventories has on average 68% with a standard deviation of +/-12%; with the most complete inventories at 83% (Bonaldo & Dias 2010;Castanheira et al 2016;Coddington et al 1991, Coddington et al 2009Ricetti & Bonaldo 2008;Rivera-Quiroz et al 2016;Silva-Davila & Coddington 1996). Paleotropical forests have on average 215.03 +/-121.71 species, with a completeness of 75.29% +/-5.9% (Malumbres-Olarte et al 2017, 2018Miller & Pham 2011;Sørensen 2004;Sørensen et al 2002). African forests are richer (215.45 species) that the South East Asian counterparts (104) (Miller & Pham 2011).…”

“…A quasi-optimized protocol for tropical forests named COBRA-TF has been recently proposed and successfully tested (Malumbres-Olarte et al 2017, 2018. This protocol distributes the collecting effort by method in function of its efficiency to capture species and recommended 36 samples to achieve accurate community measurements in plots of 0.25 ha.…”

“…Cryptic searching during the day was the most efficient method to sample ground vegetation, leaf litter, under rocks and small crevices. The contribution of pitfall traps, looking down at day, cryptic searching at night and looking up at day was very small for the analyzed tropical ecosystems; however, these methods are necessary to compare with other studies, mainly because they collect species missed by other methods (Malumbres-Olarte et al 2017, 2018.…”

Assessment of North American arthropod collections: prospects and challenges for addressing biodiversity research

“…We are not suggesting that 2,500 records are required for every arthropod species to address every question. Depending on the nature of the question, only a fraction of all available records may be appropriate either because they do not address the question or data quality issues (Piel, 2018; Veiga et al, 2017; Sikes et al, 2016; Ferro & Flick, 2015), such as data leakage with historic records (Peterson et al, 2018). Future analyses should provide more refined per species digitization targets (Lobo et al, 2018; Pelletier et al, 2018) once more digitized arthropod records become available.…”