Species Interactions in Food Webs

Ecological communities can be envisioned as food webs in which species are linked with each other in a network of interconnections. Conceivably, all organism in this network—plants, herbivores, carnivores and detritivores—are effectively predators of resources and resources for other predators. From this conception, one can deduce a fundamental rule or mechanism for succeeding in the evolutionary-ecological game of life. Namely, individuals within a species ought to exhibit flexible adaptive responses to balance fitness gains from consuming resources against fitness losses related to decreasing the risk of being consumed. This fundamental mechanism can transcend spatial and temporal scales, and taxa, but the exact way that the tradeoff is balanced will depend on local ecological context. Research in the lab focuses on how this evolutionary adaptive game determines the nature and strength of food web interactions with cascading effects on the chemical make-up of species and attendant effects on nutrient cycling through ecosystems.

How do above-ground and below-ground consumers impact nitrogen mineralization?
Researcher: Rob

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Nitrogen is a limiting nutrient in terrestrial ecosystems, and the rate which organic nitrogen from dead, decaying material is converted to highly available mineral forms can constrain ecosystem productivity. For my Masters research, I aim to quantify how the structure and complexity of terrestrial food chains impacts the rate of nitrogen cycling. The first step in my research will be to understand how the addition of nutrients to the soil impacts the rate of nitrogen cycling. This will take place in the lab. I chose this focus, because soil is the site of many important steps in the nitrogen cycle including mineralization. In complementary field experiments at Yale-Myers Forest in Northeastern Connecticut, I will expose caged, old-field plots to different aboveground and belowground community composition. In old-fields these communities contain grasshoppers (herbivores), spiders (carnivores), and springtails (microbial grazers). The results of this experiment will improve our understanding of how the structure of food chains impacts the cycling of nitrogen in terrestrial ecosystems.

Food webs, nutrient cycling, and carbon storage in the High Andes
Researchers: Julia

In the essential ecosystem process of nutrient cycling, plants and microbes are generally considered the main biotic players. Plants, of course, take up carbon from the atmosphere and nutrients from the soil, and microbes decompose decaying plant litter and return nutrients and some carbon to the soil. But what happens in ecosystems with little vegetation and almost no plant litter? Julia's research examines how large animals may play an important role in carbon and nutrient cycling in a barren alpine landscape in the High Andes of Argentina. In a system comprised of vicuñas (herbivores), pumas (predators), and condors (scavengers), Julia hypothesizes that carcasses and latrines (communal vicuña scat piles) provide important nutrient inputs into the soil, and that the trophic interactions within this food web determine the distribution and deposition rate of these inputs. She will combine soil sampling and stable isotope analysis at carcasses and latrines to evaluate the effects of puma predation and vicuña anti-predator behavior on the distribution of nutrients in the landscape. She will also use experimental placement and exclosure of carcasses to test for the effects of scavenging on nutrient inputs from carcasses. These results, when combined with an understanding of the landscape's natural geohydrological variation, should shed light on the role of animals in mediating nutrient cycling and soil carbon storage. This understanding could allow us to predict the ecosystem-level effects of species loss.

Consumptive and non-consumptive effects on Ptarmigan and indirect effects on Alaskan plants by Gyrfalcons
Researcher: Adam

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How does raptor presence affect surrounding ecosystems? This question is the primary focus of Adam’s masters thesis, which takes the theory tested by the Schmitz Lab grasshopper/spider experiments and applies it to a three-trophic rank system in the Arctic. The thesis concentrates on gyrfalcon consumption of rock and willow ptarmigan and subsequent changes to ptarmigan browsing on area shrubs. Adam will establish transects to collect data, using naturally occurring gyrfalcon territories as experimental units. Ptarmigan abundance will be recorded, differences in plant species and browsing will be catalogued, clutch size of ptarmigan nests will be measured, and ptarmigan eggs will be massed. Vegetation height surrounding nests will also be recorded, to establish visibility of nesting sites from above. Remote sensing of vegetation at increasing distances from gyrfalcon nest sites will also be used to estimate gyrfalcon effect on landscape. Field research for this experiment begins May 2017.