Print PagePrevious studies have found that invasion by the Argentine ant (Linepithema humile) was limited by low soil moisture, soil qualities, and temperature, and coincident with human habitation and sometimes vegetation. However, in many of the countries where the ant was studied, vegetation was also correlated with moist valleys, thus the studies could not clearly separate these correlated factors. Furthermore, Argentine ants could invade some mediterranean type ecosystems, but not others. Invading Argentine ants frequently locate and exploit ephemeral resources better than native ants, and thus should invade weedy disturbed grazed fields, while native ants may be better adapted to the less variable conditions of older forests. This study tested the hypothesis that native vegetation of the central coast of Chile is less permeable to invasion by the Argentine ants than disturbed farm fields.
I mapped ant invasion fronts in isolated regions of coastal Chile using a GPS and reiterative ground sampling. I overlaid this map onto a vegetation map and measured invasion distance using Google Earth. I used a paired t-test to compare permeability of adjacent landscapes to invasion by the Argentine ant. Adjacent landscape pairs consisted of grazed/oats next to old forest, and grazed/oats next to native fragment hedgerows (n=18).
Results/Conclusions
Argentine ants consistently invaded further along hedgerows and fragments of native vegetation than into weedy grazed grain fields; however Argentine ants consistently invaded further along grazed grain fields than into adjacent old forests. Native ants were not particularly abundant in the old forests suggesting that there may have been biotic resistance due to competition or predation by an abundance of spiders, which in noteworthy abundance. Since the Agricultural matirix of coastal Chile consists largly of small fields, hedgerows, and small forest fragments, the coastal landscape should be permeable to Argentine ant invasion.
