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Wilson, 1990). Kusnezov (1957) plotted the decline in species richness with latitude for
the Neotropical and Nearctic regions, and for Europe (Figure III.57a). More recent work
(see, for example, Cushman
et al
., 1993) has confirmed this general latitudinal trend.
In addition to latitudinal variation, the number of species falls off drastically with
increasing elevation and this is illustrated (Figure III.57b) with data from the Great
Smoky Mountains National Park in the USA (Cole, 1940 in Kusnezov, 1957). Even in
the tropics, ants are largely absent from forested mountains above 2500 m in elevation
(Hölldobler and Wilson, 1990). However, above the tree line, the number of species may
