Every living thing needs nutrients. Much previous work has shown that a variety of soil nutrients – in particular Nitrogen (N), Phosphorous (P), and Potassium (K) – greatly impact plant communities. Often, human behaviors, especially agricultural practices like fertilization, have generated significant shifts in these nutrients. When environments become flushed with these nutrients, overall biomass typically increases but biodiversity often decreases. This is expected according to two hypotheses:

  1. Nutrient Limitation Hypothesis: Limitations in nutrients suppress abundance, and therefore increases in nutrients will drive increased abundance.
  2. Community Homogenization Hypothesis: Species that are most efficient at utilizing resources are prevented from completely excluding other species due to resource limitations. Therefore, increases in nutrients will allow these species to competitively exclude other species, decreasing overall diversity.

Quite a bit of previous work has addressed these hypotheses in plant communities, but tests of impacts on higher trophic levels, specifically consumers, are rare. Enter Jelena Bujan and fellow researchers. In a paper recently published in Ecosphere, Bujan and colleagues tested these two influential hypotheses in the most import consumers known to man: ants.

azteca

Azteca ants congratulate each other on their dominance. Photo: Alex Wild

The researchers investigated the impact of experimentally adjusted levels of N, P, and K on ant communities in a Panamanian tropical rainforest. They found that indeed, increases in P drove both increases in abundance and decreases in diversity at the genus level, supporting both hypotheses. However, they did not find significant effects of any of the three nutrients on species level diversity, which is somewhat surprising. Bujan and colleagues suggest that the high frequency of rare species in their dataset may have confounded their ability to detect true effects at the species level, and therefore genera may serve as better groups for detecting shifts in diversity.

Interestingly, the effects detected by the researchers were driven by a single genus, Azteca. Azteca ants are a highly active and dominant group found throughout the Neotropics. Future research could reveal exactly how phosphorus uniquely impacts Azteca ants and how fluctuations in nutrients may mediate their dominant behavior.

This study by Bujan and colleagues addressed hypotheses typically applied to plant communities, and their results suggest that nutrient limitations and fluctuations have bottom-up effects through plants to consumers. Hopefully we will soon see similar studies in other ant communities!