Although agriculture is essential to sustaining human life in the Anthropocene, current farming practices can create biodiversity wastelands where conditions are inhospitable for most organisms. This can minimize the ecosystem services native species would otherwise provide to crops. Ants, for example, are important predators of crop pests in the midwestern US. To better understand the impact of agricultural intensification on ant communities, the Kellogg Biological Station Long-Term Ecological Research Site (LTER) contains replicate plots of Organic and Chemical agricultural treatments that have been maintained for 30 years. Throughout the growing season of 2019, we characterized ant communities in the LTER by placing pitfall traps throughout replicate plots of each treatment. We test whether the activity of ants—and their potential for pest regulation—varies with agricultural intensification by studying ant communities that have developed in Organic and Chemical agriculture plots. We also examine how the treatments differ in seasonal patterns of activity. Our two hypotheses explain ant activity in terms of farming practice and seasonal variation.
Hypothesis 1) The chemical fertilizers and pesticides involved in Chemical agriculture suppress ant activity relative to the Organic crops.
Hypothesis 2) Species specific ant activity reflects seasonal temperature changes throughout the sampling period.
Results/Conclusions
We found that total ant activity varied throughout the growing season (P<0.001), and Chemical plots experienced higher average ant activity than Organic plots by ~1.2 ants per trap (P < 0.001). Three common species, Lasius neoniger, Tetramorium immigrans, and Prenolepis imparis accounted for ~70% of all ant occurrences in pitfall traps. Lasius neoniger is a heat-tolerant honeydew forager, Prenolepis imparis is a cold-tolerant honeydew forager, and Tetramorium immigrans is an invasive generalist. We used these three ants to quantify our species-specific results due to their heavy presence. Organic and Chemical treatments differed in their seasonal patterns (P < 0.001). Ants in Organic plots responded to seasonal temperature patterns and exhibited low activity in the hot and dry period of mid-summer. Due to activity peaking early in the season while the crops were growing, there is potentially greater pest suppression in these plots. In contrast, ants in Chemical plots displayed erratic patterns of activity with an increasing general trend – particularly after crops were harvested. Activity in these plots peaked late in the season, indicating the possibility of less pest suppression.