Diversity and assemblage structure of phytophagous Hemiptera along a latitudinal gradient: predicting the potential impacts of climate change

Aims - The aims were (1) to assess the species richness and structure of phytophagous Hemiptera communities along a latitudinal gradient, (2) to identify the importance of rare species in structuring these patterns, and (3) to hypothesize about how phytophagous Hemiptera communities may respond to future climate change. Location - East coast of Australia. Methods - Four latitudes within the 1150 km coastal distribution of 'Acacia falcata' were selected. The insect assemblage on the host plant 'Acacia falcata' was sampled seasonally over two years. Congeneric plant species were also sampled at the sites. Results - Ninety-eight species of phytophagous Hemiptera were collected from 'A. falcata'. Total species richness was significantly lower at the most temperate latitude compared to the three more tropical latitudes. We classified species into four 'climate change response' groups depending on their latitudinal range and apparent host specificity. Pairwise comparisons between groups showed that the 'cosmopolitan', 'generalist feeders' and 'specialists' had a similar community structure to each other, but the 'climate generalists' had a significantly different structure. Fifty-seven species were identified as rare. Most of these rare species were phloem hoppers and their removal from the dataset led to changes in the proportional representation of all guilds in two groups: the 'specialist' and 'generalist feeders'. Main Conclusions - We found no directional increase in phytophagous Hemiptera species richness. This indicates that, at least in the short term, species richness patterns of these communities may be similar to that found today. As the climate continues to change, however, we might expect some increases in species richness at the more temperate latitudes as species migrate in response to shifting climate zones. In the longer term, more substantial changes in community composition will be expected because the rare species, which comprise a large fraction of these communities, will be vulnerable to both direct climatic changes, and indirect effects via changes to their host's distribution.