The Effect of Ant Nests on Plant Nutrition and Selection for Extrafloral Nectaries

University Of Alaska Fairbanks Campus, Fairbanks AK

Investigators

Abstract

Extrafloral nectaries (EFNs) are organs located on leaves and stems of plants; they secrete sugars and amino acids. Currently, the only well-accepted hypothesis for the evolution and maintenance of EFNs is that they lure predatory arthropods, especially ants, onto plant tissues and thereby reduce the damage caused by herbivores. Evidence supporting this explanation for EFNs is mixed, however. The goal of this study is to test an alternative hypothesis, the nutrition hypothesis, for the evolution and maintenance of the trait. In the North American shrub, Acacia constricta, EFNs appear to encourage ants to nest within the rooting zone of the plant, where ants can enhance soil mineral nutrient concentrations and may increase plant fitness. Some acacia individuals have ant nests at the base and others do not. Nests under acacia are dynamic, forming anew each summer. Previous work at the study site has demonstrated that ant nest soils are enriched in nutrients that frequently limit plant reproduction. The proposed research uses field and laboratory experiments to test the relative importance of nutrition and protection to correlates of fitness for A. constricta. The research also tests whether enhanced plant nutrition, provided by ant nests, feeds back to the ants through the production of high-quality food rewards. Results from this research will contribute important insights to a model system used in the evolutionary ecology of plant-herbivore interactions. The project also will contribute more generally to the role that ants play in nutrient distribution and accumulation in arid and semi-arid ecosystems. The project will provide training for a Ph.D. student and several undergraduates in the laboratory and greenhouse (University of Alaska Fairbanks) and in the field (Southwestern Research Station, Arizona). Special effort will be made to recruit native and rural undergraduates who have never had the opportunity to travel outside the state of Alaska. The project will broaden the view of ecology students by introducing them to a new biome with high biodiversity, structured by climatic challenges unlike those of their home state.