Using isotopes to track nutrients

Intrepid post-doc alum David Hoekman, who is now a staff scientist at NEON Inc., the NSF-funded center for continental scale ecology and monitoring recently wrote this piece for their blog on his research in Iceland.  Thanks David for the great summary!

Tracking isotopes to illuminate Nature’s grand recycling program


January 22, 2013


midge addition experiment

As I stand in the sun on the shore of a beautiful Icelandic lake, the wind dies down and the midges rise from their resting places in the lakeshore grasses and wildflowers. The fog of midges quickly thickens and I am soon engulfed and surrounded by the noise of millions of tiny wings buzzing around me.

…. Read More



Posted by Claudio

Bring it On! Fall 2012

With the Autumnal Equinox just around the corner (Saturday the 22nd in fact…) we find the Fall semester here at UW-Madison well under way.  The Gratton Lab has is saying “Farewell!” to our postdocs David, who has already left for NEON, and Heidi who will be leaving us shortly for Sewanee.  We’ve also added a new Master’s student in agroecology Emma Pelton who happens to like deserts among other things.

Switching gears, the Iceland Team has recently released their debut music video that we share with you below…  Enjoy!

YouTube Preview Image

PhD position available

Interested in graduate school?  Want to work at an exotic, remote field site near the arctic circle? Interested in the linkages between lakes and land. Then read on!

PhD Research Assistantship in Terrestrial Food Web Ecology

University of Wisconsin – Madison

We are looking for a motivated student interested in pursuing a PhD at the UW-Madison as part of the Gratton Lab studying the interactions between aquatic and terrestrial ecosystems.  This work takes place at a biologically rich and scenic area in northeast Iceland, centered on Lake Myvatn.  An ideal candidate needs to have a solid background in biology or ecology, have some prior research or field experience, and be able work in Iceland for summer field work.  Candidates should have interests in arthropod food web ecology, community ecology, aquatic-terrestrial linkages, linkages between below- and above-ground food webs and/or the role of arthropods in ecosystem processes.

For more information on this project visit the these links: Project linkResearch Blog

This research is part of a broad collaborative effort including Claudio Gratton (Entomology), Tony Ives (Zoology), Randy Jackson (Agronomy), Phil Townsend (Forestry and Wildlife Ecology), and Jake Vander Zanden (Center for Limnology/Zoology) at the University of Wisconsin.  Students will be applying through the Zoology program.  Graduate support would include a mix of research and teaching assistantships.

To apply, please complete this cover sheet and send this with a cover letter outlining your research interests, prior experiences and why you want to go to graduate school and join our group, CV, and names of 3 references as a single pdf file to Claudio Gratton (  Deadline: Fall 2013 TBD.

If you are planning on attending the 2013 Ecological Society Meeting in Minneapolis, MN, we can try to schedule a meeting there.


How did the Iceland project get started?

This is probably one of the most frequent questions I get when I tell people about the work we do here in Iceland. How does someone who has worked mainly in temperate areas, mostly in agricultural systems and salt marshes, with no general propensity for nordic climates (the southern European thing, you know), end up working in Iceland? Hmm, good question!

If you want to read more, click over to my recent Smidge of Midge blog post.  

Arni Claudio Randy at Kvirkfjoll

Above: Arni, Claudio and Randy (L-R).

Posted by Claudio

Undergraduate Poster Session

Yesterday the annual Biology 152 poster session took place in Union South, and three of the more than three hundred and sixty posters in Varsity Hall came from the Gratton Lab.  Heidi, Rachel, and I have been mentoring undergraduates through independent research as part of this course.  It is a lot of fun and very rewarding to work with undergraduates and help them to understand what “real” science is all about.  I think that I can speak for all of us, mentors and mentored, when I say that this has been a very very rewarding experience!


Valentine and I.









Heidi and Darin.









Rachel and Melissa.









Midges connect aquatic and terrestrial food webs

Insects live in virtually every freshwater habitat and can be extremely abundant, composing a large part of the animal biomass in lakes and rivers. Aquatic insects have important roles in food webs, acting as decomposers and consumers of aquatic plants. Many are in turn consumed by crayfish, fish, and other predators. But aquatic insects can also be important parts of food webs on land when they emerge from the water and fly over land to find mates. We’ve been studying how neighboring habitats are connected to and affect one another. When midges, mayflies, mosquitoes, caddisflies and many other aquatic insects emerge from freshwater they can become food for predators like spiders, lizards, birds and bats and many studies have shown that these predators are more abundant along the edges of streams and lakes because of the rich food source provided by aquatic insects. In addition to providing food to predators, emerging insects can also have a fertilizer effect on plant communities next to lakes and streams because they act as fertilizer when they die and decompose.


Some aquatic insects emerge all at once in large swarms, resulting in a “pulse” of insects moving from the water to shoreline food webs. We’ve been studying the consequences of this resource pulse using a group of lakes in northeast Iceland. In Iceland, the typical productivity of the land is low (lava fields and heathlands) and dotting this landscape there are lakes, some with many midges and some with few midges, a type of small aquatic insect. We measure midges coming out of lakes, how many end up on land, and how this affects plant growth and the abundance of arthropod predators (e.g., spiders, harvestmen, beetles), detritivores (e.g., springtails [photograph above], mites) and herbivores (e.g., caterpillars, plant hoppers, aphids). The members of this arthropod food web can eat live midges (predators), dead midges (detritivores) or midge-fertilized plants (herbivores).

One way we track midge resources as they move through terrestrial food webs is by measuring carbon isotopes of spiders and insects on land. Carbon from aquatic plants has a different isotopic value than carbon from terrestrial plants. Because midges develop and grow in the water, they incorporate an aquatic carbon signature and we can track their carbon as it is integrated into the terrestrial food web.

In this photo you can see some of the 1x1 m plots at our midge addition experiment.

In an experiment simulating midge deposition at high-midge lakes (in the photo above you can see David on the right near our midge addition plots at Helluvadstjorn in Iceland), recently published in Oecologia by David Hoekman and others from our Iceland group, we added midge carcasses to a low-midge heathland site.  We found that the strongest responders to the dead midge additions were  the ubiquitous springtails or Collembola, little insect-like creatures that have a habit of jumping around by flicking a little structure under their abdomens.  These tiny (<2mm) arthropods are known to be decomposers of dead and decaying organic matter, likely feeding on the bacteria and fungi growing there.  If enough midges are added (for example, if you add midges for two consecutive years), then even larger things like spiders start to show evidence of midge carbon in their tissues.  How does it get there?  Well, spiders are active predators that eat only live prey, so we surmise that they got the midge carbon in their tissues by feeding on the springtails.  We even found some evidence that midge nitrogen was picked up by some of the plants in the area where midges were added.  Once the midges are gone, however, the midge carbon quickly disappears from the system.  Within one year of the midge additions there is little evidence of midge carbon in the arthropods any more.  As the arthropods die and their offspring take their place, they new generation develops in an environment that is now midge-free. 

This research is helping us to understand how aquatic and terrestrial systems are connected. Aquatic insects are a major driver of these connections, but other prominent examples include salmon returning to their natal streams and sea birds nesting on land. We’re also interested in how food webs respond to resource pulses, specifically what components of the food web respond quickly to available resources and how ephemeral resources are stored, resulting in long-term effects.

Posted by David Hoekman and Claudio Gratton