GLOBAL PATTERNS IN LOCAL NUMBER OF INSECT GALLING SPECIES

We evaluate a three-parr hypothesis explaining why gall-inducing insec t species richness is so high in scleromorphic vegetation: (1) persist ence of low nutrient status scleromorphic leaves facilitates the galli ng habit in warm temperate latitudes; (2) favourable colonization site s for gallers result from reduced hygrothermal stress, high phenolics in the outer cortex of the gall, and reduced carnivore and fungal atta ck in the gall, and (3) in more mesic sires, mortality is high due to carnivore attack and invasion of galls by fungi, Over 280 samples of l ocal species of galling herbivorous insects from fourteen countries on all continents except Antarctica revealed a strong pattern of highest richness in warm temperate latitudes, or their altitudinal equivalent s. The peak of galling species richness on the latitudinal gradient fr om the equator into the Arctic was between 25 to 38 degrees N or S, Ga lling species were particularly diverse in sclerophyllous vegetation, which commonly had greater than twelve species per local sample. In me sic, non-sclerophyllous vegetation types the number of galling species was lower with twelve or fewer species present. Many sites in sclerop hyllous vegetation supported between thirteen and forty-six galling sp ecies locally, including campina islands in Amazonia, cerrado savanna in central Brazil, the Sonoran Desert in Arizona and Mexico, shrubland in Israel, fynbos in South Africa and coastal scleromorphic vegetatio n in Australia. At the same latitude, or its elevational equivalent, g alling species richness was significantly higher in relatively xeric s ites when compared to riparian or otherwise mesic habitats, even when scleromorphic vegetation dominated the mesic sites. The results were c onsistent with the hypothesis and extend to a more general level the p atterns and predictions on the biogeography of gall-inducing insects.