Empirical Research

Much of the empirical research in the McCann Lab asks how the processes identified by ecological theory actually play out in complex natural ecosystems. In particular, we are interested in how environmental variation, food-web structure, animal movement and spatial heterogeneity combine to influence ecosystem productivity and resilience.

Our empirical work has increasingly focused on large freshwater ecosystems, particularly lakes and the Laurentian Great Lakes. These systems provide an opportunity to study food webs across scales—from the behaviour and movement of individual consumers, to interactions among species, to the movement of energy across entire landscapes.

A central goal is to understand how organisms use variation in their environment and how these individual responses scale up to influence the structure and resilience of whole food webs.

Following Energy Through Food Webs

Food webs ultimately describe the movement of energy through ecosystems. We therefore use a combination of field sampling, stable isotopes, bioenergetics, population data and other approaches to determine where energy originates, how it moves through food webs, and which pathways ultimately support higher trophic levels such as fishes.

Importantly, these energetic pathways are not fixed.

Consumers can shift among prey, habitats and locations as environmental conditions change. A fish that feeds offshore during one period, for example, may move into nearshore habitat or exploit a locally productive patch during another. These movements continually alter the pathways through which energy flows.

Our empirical work therefore increasingly treats food webs not as static networks, but as dynamic structures that reorganize across space and time.

Movement, Variation and Adaptive Capacity

Animal movement provides one of the clearest mechanisms through which organisms respond to environmental variation.

Using telemetry and other approaches, we examine how mobile consumers track changing environmental conditions and resources across landscapes. These movements can connect habitats and food-web pathways that might otherwise operate relatively independently.

This creates an important link between individual behaviour and ecosystem resilience. When organisms have access to multiple habitats, prey resources or productive areas, they possess alternative ways of responding when conditions change.

We are particularly interested in whether this flexibility generates portfolio effects across space and time, allowing production in one habitat or food-web pathway to compensate for declines elsewhere.

Trophic Hotspots

A major focus of our current empirical research is on trophic hotspots—localized areas where physical, biological or geomorphic processes concentrate productivity and attract consumers.

Wind can concentrate plankton along shorelines. River mouths can deliver nutrients and production to lakes. Wetlands can generate highly productive food-web pathways. Thermal gradients and other physical processes can similarly create localized areas of elevated production.

Mobile consumers can find and exploit these areas, producing what we sometimes refer to as a “birdfeeder effect”: concentrated resources attract consumers and create locally intense trophic interactions.

Our research asks how often these hotspots occur, how long they persist, how strongly consumers respond to them, and how much they contribute to production at larger ecosystem scales.

Just as importantly, we ask what happens when human activities alter, disconnect or eliminate these productive areas.

The Great Lakes as Changing Food Webs

The Laurentian Great Lakes provide an extraordinary natural laboratory for understanding how food webs respond to global change.

Invasive species, nutrient changes, climate change, fisheries harvest and habitat alteration have fundamentally reorganized these ecosystems. Zebra and quagga mussels, for example, have redirected enormous amounts of production away from pelagic food-web pathways and toward the lake bottom, effectively rewiring the energetic architecture of much of the Great Lakes food web.

Our research examines how fishes and other consumers respond to this changing energetic landscape and what these responses mean for fish production, biodiversity and ecosystem resilience.

Rather than viewing these changes only as increases or decreases in individual species, we ask how environmental change is altering the structure of the food web itself.

From Empirical Ecology to Ecosystem Management

Ultimately, our empirical research seeks to identify the features of real ecosystems that generate—and maintain—adaptive capacity.

By combining measurements of food-web structure, energetic pathways, animal movement, spatial variation and environmental change, we aim to determine when ecosystems retain multiple pathways for responding to disturbance and when those alternatives begin to disappear.

This work increasingly connects directly with ecosystem management. Through collaborations with government agencies and other partners, we are working toward indicators that can detect changes in food-web structure before they translate into major losses of ecosystem function or fisheries production.

The empirical challenge therefore mirrors the theoretical one:

Can we identify, measure and ultimately protect the ecological variation that allows ecosystems to adapt to a changing world?