LATITUDINAL GRADIENTS IN PARASITE DIVERSITY: BRIDGING THE GAP BETWEEN TEMPERATE AND TROPICAL AREAS

Abstract

Although the latitudinal gradient in species richness is one of the clearest global patterns of biodiversity, evidenceto date suggests that it either does not apply to parasites, or that if it does then the relationship is weak. In this short review, I use a large database including information from 950 surveys of helminth parasite diversity in vertebrate host populations to show that there is no latitudinal gradient in parasite species richness among bird or mammal hosts, and a weak one among fish hosts going against the general trend: fish from temperate latitudes tend to harbour more helminth species than those from the tropics. However, analyses of that database also show that several disparities between temperate and tropical parasite surveys can underlie the above finding. First, surveys of parasite diversity are accumulating at a much higher rate in temperate areas than in the tropics. Second, the overall level of parasitological knowledge per host species is generally higher for temperate vertebrates than for tropical ones. Third, the taxonomic resolution achieved per survey is also generally higher for temperate vertebrates than for tropical ones. Data from temperate and tropical regions are therefore not truly comparable at present, and it may be premature to attempt any large-scale test of the latitudinal diversity gradient hypothesis, or to accept the conclusions of previous studies attempting such a test.