Abstract
AimInsects are the most species‐rich clade in the world, but the broad‐scale diversity pattern and the potential drivers have not been well documented for the clade as a whole. We aimed to examine the relative roles of contemporary and historical climate, niche conservatism, range overlapping, and other environmental factors on geographic patterns of species richness and phylogenetic structure, for insects across China.LocationChina.MethodsWe collected insect data from 184 nature reserves and examined geographic patterns of species richness and mean root distance (MRD, a metric of the evolutionary development of assemblages) for different biogeographic affinities (Palearctic, Oriental, and widespread species) and for clades originated during the warm and cold geohistorical periods (“warm clades” and “cold clades,” respectively). We related richness and MRD to contemporary and historical climate, area, habitat heterogeneity, and human disturbance to evaluate their relative importance.ResultsTotal species richness revealed a hump‐shaped latitudinal pattern, peaking between 30°~35°N. Richness patterns differed markedly among evolutionary groups: Oriental species richness decreased significantly with higher latitude but Palearctic species increased, while other groups again peaked between 30°~35°N. The range overlapping of different biogeographic groups in midlatitudes may be an important contributor to humped latitudinal richness patterns. MRD was positively related to latitude and increased more rapidly for “warm clades” than “cold clades.” Historical climate factors (especially winter coldness) were among the strongest predictors for both richness and phylogenetic patterns, for each evolutionary group, suggesting the strong influence of niche conservatism.ConclusionsThe hump‐shaped latitudinal pattern of insect richness in China is mainly shaped by niche conservatism and range overlapping, supplemented by habitat heterogeneity and contemporary climate. The role of niche conservatism and range overlapping may have been overlooked if only total species richness was analyzed, suggesting the importance of examining different evolutionary groups separately.
Highlights
Species richness is generally reported to peak at the tropics and decline as latitude increases in the northern and southern hemisphere, for a number of taxa (Chown & Gaston, 2000)
We found that the mean root distance (MRD) for “warm clades” increased more rapidly along latitudinal gradient than that of the “cold clades,” suggesting that the insect orders that were originated during a warm historical climate have experienced stronger filtering since the global cooling initiated at the end of the Eocene (Ricklefs, 2005; Appendix S2)
We suggest that the range overlapping of different biogeographic affinities between 30~35°N is an important contributor to the humped latitudinal gradient of overall insect richness. (b) Studies have repeatedly suggested the Hengduan Mountain Ranges as a speciation center in East Asia, and the Qinling Mountain Ranges were considered as an important species dispersal corridor during historical climate change (Norton, Jin, Wang, & Zhang, 2011)
Summary
Species richness is generally reported to peak at the tropics and decline as latitude increases in the northern and southern hemisphere, for a number of taxa (Chown & Gaston, 2000). This latitudinal diversity gradient (LDG hereafter) has long been a theoretical focus in macroecology and biogeography since it was first observed by von Humboldt in 1874. A recent study on global grasses LDG showed that the richness of Poaceae was lower in the tropics and higher in the midlatitudes of both northern and southern hemispheres (Visser et al, 2014). If the current hypotheses on LDG (see below) are really general ones, they should be able to explain the “classical” LDG and the “exceptional” latitudinal patterns
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