Claudio Gratton - US grants

Ecological theory predicts that predation in a given location will be stronger than expected when predator populations are supported by resources outside that location (e.g., alternative species of prey). This is because external resources may allow predator populations to build even though local resources are scarce. This situation can occur when mobile predators frequently move between different habitats. Movement between multiple habitats allows predators to use resources both within and outside of a prey's habitat, allowing their populations to build (even if local conditions are bad) and strongly suppress prey.

Despite its theoretical importance, there has been little research in terrestrial habitats investigating the influence of predator movement on the intensity of predation in local habitat patches. This research will examine the question experimentally by decreasing and increasing movement of predators between crop habitats and native prairie grass; the investigators will then observe the resulting impact on predation within crops. The goal is to determine if natural areas outside of crops provide resources that enhance predation on insect pests within a crop habitat. If this is the case, restoring natural areas in agricultural landscapes could reduce the need to use insecticides to control pests.

Non-Technical Abstract: C.Gratton
Proposal Number: DEB-0717148
Proposal Title: Linking Lakes to Land: Understanding the Spatial and Temporal Aspects of Allochthonous Subsidies


Our understanding of how lakes and land are linked is poor, despite the fact that lakes are important components of many terrestrial landscapes. Most research to this point has focused on how watershed characteristics or land use affect downstream surface waters, but we know little about reverse interactions. This study will investigate lake-to-land linkages at Lake Mývatn, a nutrient-rich lake in Northern Iceland with exceptional, natural, large-scale midge (aquatic insect) outbreaks that occur every 5-7 yr. During these outbreaks, millions of midges enter surrounding terrestrial ecosystems, where they affect everything from plant productivity to herbivorous insects and their spider predators. Through a series of manipulative experiments, remote sensing analyses, and empirical modeling, this system will serve as a model to study ecological linkages at the landscape scale and will address the fundamental question of how food webs on land are influenced by energy, materials, and organisms originating from separate and distinct lake ecosystems. Broadening our studies of terrestrial communities to explicitly include interactions with other elements of the landscape will allow us to better understand and manage our environment by considering multiple habitats simultaneously. Landscapes are being altered via both natural (e.g., invasive species) and anthropogenic forces (e.g., urbanization or agriculture). Determining how these dynamic patchworks of habitats affect each other will be essential to understanding how disturbances propagate through landscapes and to better managing our terrestrial ecosystems.

Understanding populations that undergo fluctuations in abundance from one year to the next continues to challenge ecologists. This study will investigate midges in Lake Mývatn, Iceland, to determine why their abundance fluctuates over 5 orders of magnitude in irregular cycles lasting 4-7 years. Juvenile midges feed on algae at the bottom of the lake, and experiments that encompass a full peak-to-peak midge cycle will be initiated to test the hypothesis that the extreme midge fluctuations are caused when the larvae consume all the algae. The research will also investigate the consequences of the midge cycles. During high midge years, over 300 metric tons of midges are deposited in the surrounding heathland, providing food for predators and nutrients for plants. This provides a natural experiment to test hypotheses about how the lake and shoreline ecosystems interact by observing how the pulses of midges ramify through the ecosystem networks.

The research will strengthen international collaborations with scientists in Iceland. It will train US graduate and undergraduate students doing work at Mývatn, providing them exposure to challenging scientific questions whose answers require expertise from several disciplines. Students will work in both aquatic and terrestrial habitats under the tutelage of an interdisciplinary and international research group.

This Integrative Graduate Education and Research Traineeship (IGERT) award trains the next generation of interdisciplinary scientists to design biodiversity conservation strategies in the face of novel environments, and develops an integrative program of experiential learning, engaged scholarship, and problem-focused research on biodiversity conservation.

Intellectual Merit: Humans are now the dominant biogeographic, evolutionary, and climatic force on Earth. As we change the environment ever more rapidly, new climate conditions are emerging that have no historical analogs, novel ecosystems are flourishing, and people are creating new land use patterns and demographic, economic, and political realities. This program will support a community of practice in which social scientists, climatologists, ecologists, computer scientists, geneticists, economists, statisticians, remote sensing specialists and others collaborate in interdisciplinary teams to find solutions for future biodiversity conservation in novel environments.

Broader Impacts: This IGERT award advances discovery and understanding by integrating research and experiential learning, and by establishing and strengthening collaborations among disciplines within UW-Madison, and with partners in government, conservation organizations, and abroad. A participatory research approach will ensure broad dissemination of findings, thereby enhancing scientific understanding and social benefits. A suite of new graduate seminars will train students in collaborating, and in communicating with broader audiences, and in integrating research and education. Continuing feedback from agencies and communities will ensure that results are relevant for policy formulation at both state and national levels, and program elements have been designed to engage students from underrepresented groups in partnership with existing on- and off-campus organizations.

IGERT is an NSF-wide program intended to meet the challenges of educating U.S. Ph.D. scientists and engineers with the interdisciplinary background, deep knowledge in a chosen discipline, and the technical, professional, and personal skills needed for the career demands of the future. The program is intended to establish new models for graduate education and training in a fertile environment for collaborative research that transcends traditional disciplinary boundaries, and to engage students in understanding the processes by which research is translated to innovations for societal benefit.

Dramatic 'outbreaks' of organisms - locusts, lemmings, insects - draw public attention to the natural world, in part because scientists do not completely understand the causes for these population surges. This study will investigate midges in Lake Mývatn, Iceland, and why their abundance fluctuates over 4 orders of magnitude in irregular cycles lasting 4-7 years. Adult midges that emerge from the lake die on shore. During high-midge years, the weight of midges that are deposited in the surrounding heathland is equivalent to 10 humpback whales, providing food for predators and scavengers, nutrients for plants, and the basis for local agriculture. By synthesizing results from field samples and experiments over several population cycles, this project promises new insights into fundamental scientific questions about the causes and consequences of population outbreaks. The project will engage graduate and undergraduate students who will work at Mývatn each summer, providing them exposure to extreme biology as well as to educational diversity, as they work in both the lake and on the shoreline under the tutelage of an interdisciplinary group of scientists. The public will learn more about midge outbreaks through an ongoing 'Smidge of Midge' blog.

Ecosystems that show huge changes through time can reveal the ecological forces that stabilize or destabilize natural dynamics. This project involves both long-term data collection in aquatic and terrestrial systems and targeted experiments to test specific hypotheses. The aquatic data collection will build and expand on an existing database that dates back to the 1970s. The project has added weekly monitoring of many additional variables, including midge larvae density, benthic primary production, and pelagic nutrients. The collection of terrestrial data has continued with the monitoring of midge infall and arthropod communities along transects around the lake that were established in 2008. A suite of targeted experiments will address a wide range of research questions such as (i) the role that midges play as ecosystem engineers, changing benthic conditions to favor large-bodied epibenthic cladocerans over small-bodied infaunal species, (ii) the mutualistic effect that midge larvae have on algal growth, and (iii) the importance of midge adults for the flowering of carnivorous plants. These experimental projects are led by graduate students as part of their PhD theses, and by undergraduate interns as independent projects. This combination of aquatic and terrestrial experiments together with regular sampling will test hypotheses about how the lake and shoreline ecosystems are linked together. The research will examine whether the instability of the lake ecosystem could drive instability of the surrounding ecosystem on land.