Abstract
Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.
Highlights
It is well documented that species richness varies with latitude (Willig et al 2003; Currie et al 2004b; Mittelbach et al 2007)
The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness
The latitudinal gradient in species richness is among the best-known and moststudied patterns in ecology, large-scale comparisons of local communities remain scarce (Willig et al 2003; Hillebrand 2004)
Summary
It is well documented that species richness varies with latitude (Willig et al 2003; Currie et al 2004b; Mittelbach et al 2007). Broad-scale patterns of species richness are often correlated with contemporary climate (Gaston 1996; Hawkins et al 2003; Brown et al 2004; Hawkins et al 2007). Other factors such as disturbance, history, climatic history, and geography can affect patterns of richness in addition to or independent of the effects of contemporary climate. If this is the case, richness should differ among regions after differences in contemporary climate are accounted for. Richness should vary little among regions (Qian et al 2005) and hemispheres (Chown et al 2004) once contemporary climate is accounted for, if contemporary climate alone is a sufficient correlate of richness
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