Point-diversity, a critical tool for assessing dynamics of guilds of scavenging ants (Hymenoptera: Formicidae): an example from a eucalypt woodland

Abstract

Point diversity provides essential information about structuring of assemblages and interactions of component species, not achieved using other scales of analysis. A baited grid was used (1) to ascertain number of species of scavenging ants at point resources of food in an Australian eucalypt woodland at three times in the diel cycle and (2) to assess the nature of interactions and ecological impact of each species. Nineteen measures of assemblage structure and species' interactions were implemented. Ants covered the entire area during a single diel cycle. Eurydielic species foraged over the largest area and showed least overlap. Nocturnal species foraged over the smallest area, with half the space not visited. Many foraging ranges of species-pairs, both of nocturnal and of diurnal ants, overlapped as expected by chance but half the eurydielic species-pairs overlapped less than expected; some abutted. Foraging ranges of eurydielic and nocturnal species did not overlap more than by chance. Overlap between eurydielic and diurnal species-pairs varied from less to more overlap than by chance. Simultaneous co-occurrences of all eurydielic species-pairs and many of nocturnal and diurnal ones were random. Members of pairs of nocturnal and of diurnal species were negatively associated except for one positive association. Early occupancy by diurnal ants did not guarantee persistence. Eurydielic species fed a higher percentage of their time than did diurnal or nocturnal species. Incidence of mobilization decreased with increasing number of simultaneously co-occurring species. Some species may be attracted by other species' activities. Eurydielic species dominated two tiers of diurnal species by day and two tiers of nocturnal species by night. Eurydielic species were most important in determining assemblage structure. Formicines had the greatest species richness but myrmicines and dolichoderines were more important ecologically.