Seedling recruitment in a semi-arid Patagonian steppe: Facilitative effects of refuse dumps of leaf-cutting ants

Abstract

Question: What is the influence of refuse dumps of leafcutting ants on seedling recruitment under contrasting moisture conditions in a semi-arid steppe? Location: Northwestern Patagonia, Argentina. Methods: In a greenhouse experiment, we monitored seedling recruitment in soil samples from refuse dumps of nests of the leaf-cutting ant Acromyrmex lobicornis and non-nest sites, under contrasting moisture conditions simulating wet and dry growing seasons. Results: The mean number of seedling species and individuals were higher in wet than in dry plots, and higher in refuse dump plots than in non-nest soil plots. The positive effect of refuse dumps on seedling recruitment was greater under low moisture conditions. Both the accumulation of discarded seeds by leaf-cutting ants and the passive trapping of blowing-seeds seems not explain the increased number of seeds in refuse dumps. Conversely, refuse dumps have higher water retention capacity and nutrient content than adjacent non-nest soils, allowing the recruitment of a greater number of species and individual seedlings. Conclusions: Nests of A. lobicornis may play an important role in plant recruitment in the study area, allowing a greater number of seedlings and species to be present, hence resulting in a more diverse community. Moreover, leaf-cutting ant nests may function as nurse elements, generating safe sites that enhance the performance of neighbouring seedlings mainly during the driest, stressful periods.