THE MACROECOLOGY OF AUSTRALIAN FROGS

1. The Australian continent provides an important test of macroecologi cal patterns given its unique biota and long-term geographical isolati on. However, macroecological contributions from the Australian contine nt are rare. We explored the relationship between abundance and geogra phical range for Australian frogs (Order Anura) across complete geogra phical ranges, and investigated how adult body size relates to both ab undance and the size of geographical ranges. 2. Our analyses followed two complementary paths. First, we employed cross-species correlations at a number of taxonomic levels to analyse present-day ecological ass ociations among the macroecological variables. Secondly, we tested whe ther there were correlated evolutionary divergences among the variable s by use of the phylogenetic regression. In the event, cross-species p atterns and correlated divergence patterns proved quite similar for th is dataset. 3. For Australian frogs there is a strong, significant pos itive correlation between abundance and geographical range, that is no t mediated through body size, and that is found for both cross-species correlations and as correlated evolutionary divergences. Among biolog ical mechanisms that have been proposed, some can be rejected. Feasibl e explanations would invoke resource use or intrinsic rates of increas e or both. 4. There is also a significant positive correlation between adult body size and geographical range. We were able to discard four of the five proposed mechanisms describing this relationship. The rema ining mechanism relates to homeostasis and environmental variability. 5. Previous studies of the relationship between adult body size and ab undance have revealed a strong negative correlation when studies are p erformed over areas that encompass most or all of the geographical ran ges of the species in question. Contrary to these studies, a negative relationship was not found for Australian frogs. None of the eight exp lanations postulated from other studies can account for this discrepan cy, leading to the conclusion that Australian frogs provide a contrast to macroecological patterns prevailing elsewhere. 6. Body size could not explain directly the relationship between abundance and geographic al range. While there was a significant positive correlation between b ody size and geographical range, there was no relationship between bod y size and abundance. If a mechanism incorporating the intrinsic rates of increase of species is to explain the positive relationship betwee n abundance and geographical range, then ecological factors other than body size must be determining differences in intrinsic rates of incre ase.