Fifty-seven to 65% of the endemic species sampled in these communities had population
densities that fall below this threshold, placing them at high risk. For introduced species, the trend HDAC inhibitor mechanism between population density category and probability of drastic decline was weaker. Introduced species that occurred at relatively low population densities appeared to be much less vulnerable than corresponding endemic species, but vulnerability was fairly similar for higher density introduced and endemic species. Fig. 1 Relationship between arthropod population density and likelihood of drastic population decline (defined as having at least 90% of all individuals captured in uninvaded plots). Species are grouped by density GANT61 cell line categories; numbers in parentheses indicate number of species in each category. Gray bars show the observed percentage of species exhibiting
patterns of drastic decline. Horizontal lines within gray bars show the percentage of species expected to exhibit patterns of drastic decline purely by chance. Above population densities of about 9–14 individuals, this latter percentage essentially drops to zero. Black dots connected by lines show the chance-corrected likelihood of drastic decline for each category (calculated as the observed percentage minus the percentage expected by chance) Taxonomic trends and variability Several taxonomic orders in these arthropod communities stand out as being particularly vulnerable to invasive ants, when accounting for provenance. Endemic beetles selleck inhibitor (Coleoptera) and spiders (Araneae), both rare and non-rare species, were strongly reduced in invaded areas with high consistency (Tables 3, 4). In addition, endemic barklice (Psocoptera) and non-rare endemic moths (Lepidoptera) were more likely than not to be strongly reduced in invaded areas. Several additional orders had high rates of negative
impact, but these were represented second by single species, making it difficult to draw conclusions. Overall, at least one endemic species in each order was strongly impacted at one or more sites. Among introduced species, only Hymenoptera (bees, wasps and a pair of relatively uncommon ant species) were consistently impacted by ants. The remaining orders were much more variable among species in the inferred responses to ant invasion. Table 3 Responses of non-rare species to ant invasion, grouped by taxonomic ordera Class Order Impact scoreb Rate of pop variability (%)c % negative % weak % positive % variable (a) endemic species Arachnida Araneae 100(5) 0(0) 0(0) 0(0) 0 Diplopoda Cambalida 100(1) 0(0) 0(0) 0(0) na Entognatha Collembola 42.8(3) 28.6(2) 0(0) 28.6(2) 100 Insecta Coleoptera 100(3) 0(0) 0(0) 0(0) na Insecta Diptera 20.0(1) 20.0(1) 20.0(1) 40.0(2) 100 Insecta Hemiptera 47.6(10) 19.0(4) 14.3(3) 19.