RESPONSES OF HARVESTER ANTS TO HABITAT DEGRADATION IN THE MONTE DESERT, ARGENTINA

RODRIGO POL; LUIS MARONE

Curitiba

Simposio; XXIII Simpósio de Mirmecologia; 2017

Human-induced rapid environmental change may decrease food resources and create unfavorable conditions for native species. Organisms showing a flexible foraging behavior can exploit novel or alternative foods and are more likely to persist, whereas less flexible organisms might suffer starvation and numerical reductions. This study assessed whether declines in the quality and availability of seeds prompted by grazing provoke behavioral and numerical responses in Pogonomyrmex mendozanus ants, and aimed to test whether behavioral flexibility buffers habitat degradation and prevents numerical declines. We assessed behavioral (diet, foraging activity and foraging success) and numerical (colony size and colony density) responses of harvester ants to changes in the size and composition of soil seed banks in two areas which had been historically subjected to contrasting grazing pressure in the Telteca Natural Reserve, central Monte desert, Mendoza, Argentina. Heavy grazing caused seed reductions, especially of the highly consumed and preferred grass seeds, and triggered two kinds of ant responses. Ants expanded their diet by incorporating a greater proportion of non-seed items, and they reduced foraging activity. As a consequence, the rate of food intake per colony lessened, particularly that of carbohydrate-rich seeds like grass seeds. The number of broods per colony remained the same between conditions, but the number of workers declined under heavy grazing. Colony density also fell, with a high reduction (84%) in the heavily grazed areas. Habitat degradation triggered a cascade of mechanisms that starts with a decrease in the seed resources and continues with changes in ant behavior. However, behavioral responses were insufficient to prevent ant numerical declines. The results of this study suggest that the reduction in the colony size and colony density under habitat degradation was provoked by ant nutritional deficit and starvation, and predict a deterioration in body condition, colony performance and reproduction of ants, which deserve further assessment. (ANPCyT, PICT 2013-2176, PUE 042; CONICET, PIP 2012-469; Universidad de Buenos Aires, UBACyT 20020130100809BA; Universidad Nacional de Cuyo, SeCTyP 2016-2018).