Biogeochemical drivers of Neotropical ant diversity and abundance
Chemical elements are building blocks of every living organism and yet, we know little about the effects of biogeochemistry on higher level consumers in forest ecosystems. We explored the effect of biogeochemistry on ant activity and community structure. We tested the nutrient limitation hypothesis – adding a limiting nutrient increases ant activity and abundance, and the community homogenization hypothesis – adding a limiting nutrient decreases ant diversity. We used a long term fertilization experiments in a secondary lowland rainforest on the Gigante Peninsula in Panama where nitrogen (N), phosphorus (P) and potassium (K) were added in a factorial design. We predicted higher activity but lower diversity on the fertilization plots of a lowland rainforest, which is expected to be P limited. At each of the 32 fertilization plots we set up two linear transects and baited trees and lianas to attract both canopy and litter ants.
After controlling for temperature, which explained roughly 20% of ant foraging activity, P addition was found to significantly increase ant foraging activity. This pattern was largely driven by highly abundant genus Azteca which increased its foraging on all plots receiving P. Ant diversity was significantly lower on P plots compared to all other treatments, supporting the “paradox of enrichment” frequently observed in plant communities. The observed higher ant activity, and lower diversity on P plots suggests that ants are tracking the nutrient limitation of the ecosystem. The strong influence of soil biogeochemistry on these ubiquitous insects is not only important for ant community composition but has potential ramifications for entire food webs.