The chemical composition of living organisms reflects their evolution, their traits, and the environment in which they exist. Differences in the availability of certain resources, and in particular a scarcity of a chemical resource that is critical for the expression of a particular trait, may restrict the abundance of some species. The extent to which a specific set of traits, starvation resistance, worker size, colony size, colony growth rate, and colony tempo, is linked to chemical composition and nutrient availability will be tested in a diverse community of litter ants in a lowland tropical rainforest of Panama. Experimental manipulations of particular nutrients will be used to test whether nutrient availability can shift the species composition of the ant community in ways that are consistent with observed correlations between species traits and chemical composition.
This project in tropical biodiversity science is an excellent entry point to evolutionary ecology for students, and undergraduates will participate in all phases of the research. The familiarity and experimental tractability of ants make them an ideal instructional tool, and the multiple research foci of the project will provide opportunities for students to acquire a diversity of skills. The field work, set on Barro Colorado Island in Panama, will expose students to the dynamic research culture of an international field station. Together, these experiences should provide students with the skills, knowledge, and motivation to pursue a career in science.
In any given ecological community, species exhibit an enormous diversity in the ways they make a living. A key goal in ecology is to understand why this diversity exists and how we can use it to predict changes in future communities. Our proposal focused on one of the most ecologically important insects--the ants--in the most diverse terrestrial habitat on earth: tropical rain forests. We tested two broad hypotheses: that the different ways of making a living (e.g., where an ant colony lived, how fast it ran, how it mixed plants and animals in it's diet, how susceptible it was to infection) required different chemical recipes, and that biogeochemistry--the mix of available elements as one moved from habitat to habitat--provided a template allowing an ecologist to predict the abundance and kind of ants in those habitats. Those hypotheses bore fruit in a number of ways. Many of them involved comparisons of two very different habitats that exist 40 m apart in any tropical forest: the canopy and the understory below it. The tropical canopy is a bright, hot, and variable environment, criss-crossed with runways and full of the carbohydrates pumped out by photosynthesis. The litter is shady, receiving 1/100th of the sun hitting the canopy, and receives a constant rain of dead bodies, feces, and other detritus. This has big consequences for the ways that ants make a living. We showed that understory ants, when provided plots laced with sugary carbohydrates, protein, or both, responded only to the sugars. Sugar plots had more ants and were increasingly dominated by a species that has proven to be an invasive on islands where it has been introduced. Despite the importance of protein to the diet of all consumers, sugars were sufficiently rare in the understory (compared to the canopy) to be the sole limiting macronutrient. Increases in carbohydrate availability in a warmer, more carbon rich world may thus shift the composition of ant communities by favoring a handful of species best able to find and defend these energy rich patches. A major concern in a warming world involves temperature tolerances. A leading hypothesis is that tropical species, living in an ever-warm environment, have become specialized to a narrow range of temperatures (in the same way that the wardrobe of a family living in Panama would be less variable than one living in Nebraska). If so, the hypothesis goes, tropical species may be paradoxically vulnerable to a 10F increase in air temperature, as they only experience temperatures from 75-90F. We showed that tropical worker ants are remarkably heat tolerant, with many able to endure temperatures more than 30F higher than the predicted in climate models. The reason is fascinating: tiny ants live on surfaces that heat up to be far warmer than the surrounding air. They are thus pre-conditioned by their environment to be heat tolerant. And, getting back to biochemistry, the ants most able to endure temperature lows and highs appear to be predators, those that eat more meat, and thus have a more nutritionally balanced diet. Ants are so common they can also be agents of change in the distribution of biogeochemistry. One stunning example involves Azteca ants. Azteca live in colonies of tens of thousands of ants, with nests built of paper, much like wasps, that are suspended above the forest floor. The Azteca workers roam through the canopy, harvesting sugary liquids and insects, bringing them back to the nest where they feed their young. The inevitable waste products are deposited, in a steady stream, directly below the nest. As a consequence, these ants are a conduit of concentrated resources, collected over a diffuse area above, but poured down onto a meter square or so of forest soil. The Azteca thus provide a dependable hotspot of activity for the ecosystem, where understory ants and other invertebrates collect to dine on the resources, and enhance the rate of decomposition. In sum, in the above work and in some not reported here, we show that an understanding of the basic nutritional ecology of ants yields numerous insights into the diversity of this important group and their effects on the functioning of one of Earth's most diverse ecosystems. Finally, this collaboration between Kay (a junior professor at a 4 year college in Minnesota) and Kaspari (a senior professor at a Ph. D. granting institution in Oklahoma) had a strong educational component. It allowed Kaspari to mentor Kay, and both to mentor a undergraduates and graduate students from both schools. One such student, Jane Lucas, earned a "best undergraduate presentation" award at the Entomology Society for America meetings, and virtually every scientific publication that arose from this work was co-written by students.
