Host specificity of temperate and tropical animals

Abstract

Many groups of animals show a gradient of increasing species richness from polar to equatorial regions^1,2. Theory^3,4 suggests that species should be more specialised ecologically in the tropics. Most of the evidence for this comes from studies on birds^5–10. Birds appear to subdivide the habitat more finely and specialise more in their food in the tropics. It has been suggested¹¹ that tropical Papilionidae (Lepidoptera) are more specialised in their hosts than temperate species, but host specificity was considered only at the level of the plant family, and more detailed studies of a wide range of butterflies¹² suggest that they are little (if at all) more specialised in their food plants in the tropics. Similarly, monogenean trematode parasites of fish show no change in the degree of host specificity at different latitudes¹³. Here it is shown that one group of insects, the bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae), are less host-specific in the tropics than in temperate regions, even though there are considerably more species present in the tropics. The ‘reverse’ latitudinal gradient in host specificity can be related to the greater proportion of relatively non-specific xylomycetophagous species (ambrosia beetles) in the tropics and to the greater heterogeneity of tropical forests which will make host specialisation more difficult.