Collaborative Research: RUI - Emergent Properties of Biomass Pulses: Uncovering the Ant-mediated Effects of Periodical Cicadas on Forest Ecosystems

In nature, populations of plants and animals occasionally explode in numbers, providing a temporary surplus of nutritious food for consumers. When these nutritional ‘pulses’ occur, they can initiate chain reactions in food webs, as consumers switch from their normal diets to feast instead on the abundant new food items. Understanding the consequences of these food pulses for natural communities – which organisms are affected, for how long, and if they stop performing their normal “jobs” to take advantage of the new resource – can provide insights into how ecological systems function and respond to change.

The synchronized emergence of billions of periodical cicadas every 13 or 17-years in the eastern U.S. provides an enormous pulse of insect food for a variety of generalist consumers. The assembled research team will be the first to document the impacts of cicada pulses on the foraging behaviors and population dynamics of one of the most abundant animals on the planet: ants.

Results of the study will advance our understanding of how nutrient pulses alter the varied ecosystem services that ants routinely provide, many of which are relevant for both the forestry and agriculture sectors. In addition to training undergraduate researchers in field biology, the research team has created a free digital education program, “Friend to Cicadas,” the goal of which is to train and empower teachers throughout the entire range of periodical cicadas to provide activities that spark wonder and curiosity in their students.

In this study, the researchers test the hypothesis that most ants will opportunistically adjust their foraging to capitalize on abundant cicada prey, both during the dramatic spring emergence and again when the next generation of cicadas hatches later in the summer. Further, they predict that changes in ant foraging will alter the strength of their competitive and mutualistic interactions, initiating chains of indirect effects in the forest community.

Using a combination of direct foraging observations, nutrient baiting, ant exclusion experiments, pitfall trapping, and isotopic analyses, the researchers will quantify the impacts of these biomass pulses on ant foraging at both the population and community levels. Within- and between-years comparisons will enable the team to gauge the impacts of cicada pulses on ant-mediated ecosystem functions, foraging dynamics, and ant-ant interactions.

Specifically, the team will document the indirect effects that are likely to occur if shifts in foraging alter seed dispersal, scavenging, and protective services provided to aphids. Using stable isotopes to quantify the trophic position of ant foragers in both emergence and non-emergence years will allow the team to test whether ants initially occupying a range of trophic positions converge when fed a common diet.

Moreover, these biomass pulses present a unique opportunity to examine the context-dependency of species interactions in both mutualistic and competitive settings. Taken together, these findings will contribute to the very limited literature describing the impacts of resource pulses on terrestrial invertebrates and provide important insights into how trophic ecology is altered during, and subsequent to, nutrient pulses.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.