Abstract:
Invasive ants are a serious ecological problem around the world. The Argentine ant has
had devastating effects on resident ant communities and may negatively impact other
invertebrates in its introduced range. First detected in Auckland in 1990, this invader has
since spread widely around the country. The effect of Argentine ants on invertebrates in
New Zealand was investigated by comparing ground-dwelling arthropod species richness
and abundance between and among paired uninvaded and invaded sites in seven cities
across this invader's New Zealand range. In order to study density-dependent effects,
invaded sites were chosen so as to differ in Argentine ant population density. The effects
of rainfall and mean maximum temperature on Argentine ant abundance and the species
richness and abundance were also examined. Argentine ant population persistence in
New Zealand was examined by re-surveying sites of past infestation across this species
range. The influence of climate on population persistence was investigated, and how this
effect may vary after climate change. Additionally, the potential of community recovery
after invasion was also examined. Epigaeic (above ground foraging) ant species richness
and abundance was negatively associated with Argentine ant abundance; however, no
discernable impact was found on hypogaeic (below ground foraging) ant species. The
effect of Argentine ant abundance on non-ant arthropod species richness and abundance
was mixed, with most arthropod orders being unaffected. Diplopoda was negatively
influenced by Argentine ant abundance while Hemiptera was positively influenced.
Annual rainfall and mean maximum temperature were found to have no effect on
Argentine ant abundance or resident ant species richness and abundance, though these
variables did help explain the distribution of several non-ant arthropod orders. Argentine
ant populations appear to be collapsing in New Zealand. Populations had a mean survival
time of 14.1 years (95% CI= 12.9- 15.3 years). Climate change may prolong population
survival, as survival time increased with increasing temperature and decreasing rainfall,
but only by a few years. Formerly invaded Auckland ant communities were
indistinguishable from those that had never been invaded, suggesting ant communities
will recover after Argentine ant collapse.
