QUANTIFYING THE FOOTPRINT OF A DOMINANT ORGANISM: IMPACTS OF LEAF CUTTER ANTS ON BIOGEOCHEMICAL CYCLING IN TROPICAL FORESTS

One of the most conspicuous features of a tropical forest is the abundance of leaf cutter ants. Their networks of trails extend throughout the forest and workers walk single-file, carrying pieces of leaves into their nests, where special fungi break down the plant material and produce hyphae, on which the ants feed. Leaf cutter ant nests are massive in size and during nest construction and maintenance, ants mix soil particles and alter soil chemistry. Leaf cutters are also the dominant herbivores in tropical forest ecosystems, bringing 10-50 % of all surrounding vegetation into the nest, fertilizing nest soils, and promoting the release of carbon dioxide into the atmosphere. Leaf cutter ant activities can therefore influence ecosystem carbon dynamics, though their influence remains unquantified. To address this knowledge gap, carbon dynamics inside leaf cutter ant nests will be compared to areas without ants. This information will be used to model how leaf cutter nests influence soil and atmospheric carbon dynamics across a range of tropical ecosystems.

Leaf cutting ants are increasing in abundance in tropical and subtropical ecosystems that cover 17% of the Earth’s land mass and store approximately 40% of all carbon, much of it in soil. The global climate is changing and of particular concern is the potential influence of climate change on soil carbon dynamics. Understanding the contribution of an ecologically important ant species helps address a critical knowledge gap in the global carbon cycle and improve predictions of future carbon dynamics.

Workshop: Leaf cutter ants and ecosystem processes

July 2015, la selva, costa rica

In this workshop, six scientists worked with students from the United States and Costa Rica to explore the links between leaf cutter ant activities, microbiology, biogeochemical cycling, and ecosystem processes. The workshop was divided into three modules: Part I reviewed the field of microbial ecology through the application of microbiology laboratory and field methods. Part II focused on the technical aspects of measuring mycorrhizae and Part III went over techniques to measure soil carbon fluxes and pools. Together, this workshop brought together focused seminars and hands-on laboratory and field exercises to answer ecological questions, encouraging students to develop independent research questions and test them in a tropical forest ecosystem.

Faculty: Dr. Adrián Pinto Tomas, University of Costa Rica, San José

              M.Sc. Catalina Murillo Cruz,  University of Costa Rica, San José

              Dr. Michael Allen, University of California, Riverside

              Dr. Steven Oberbauer, Florida International University, Miami               

              Dr. Thomas Harmon, University of California, Merced


SITE INSTALLATION, LA SELVA RESEARCH STATION, COSTA RICA - AUGUST 2014

In August 2014, the entire research group met in La Selva to finish plot selection and install the long-term sensor network. In two weeks of intensive field work, we accomplished a lot. We:

(1) selected focal Atta cephalotes nests that will be measured for the duration of the project

(2) installed lysimeters that will collect soil water from 3 soil depths (20cm, 60cm, and 100cm deep) and give us information about carbon losses in dissolved organic and inorganic forms across time

(3) installed gas wells that will allow us to collect soil CO2 from 3 soil depths (20cm, 60cm, and 100cm deep) and tell us not only about soil CO2 concentrations but allow us to measure stable C isotopes

(4) installed soil moisture and temperature probes across a depth profile

(5) extracted soils to quantify fungal infection, collected soil invertebrates associated with Atta cephalotes nests, and exported soils to quantify microbial communities and soil enzyme activity

(6) selected our "super" site, where we will embed an extensive sensor network providing real-time continuous measurements of CO2 diffusion and efflux (embedded soil profile soil CO2 sensors), root and hyphal dynamics (mini-rhizontrons), soil moisture and temperature dynamics, and small cameras that will track ant activity 

Taking advantage of the opportunity to brainstorm on the ground, we planned our research campaigns for the next year. Most importantly, we mapped out the long-term vision for how all the discrete data pieces fit together into the modeling framework to quantify the influence of leaf cutters at an ecosystem scale. All in all, this trip was a resounding success and we are leaving La Selva energized and excited about the research ahead!