Stefan

Stefan Sommer | Research Assistant

I am an experimental biologist contributing to projects that aim at prediciting and resurrecting population responses to environmental change. I conduct laboratory experiments, supervise students, and assist in teaching.

 

ResearchGate | ORCiD

 

CV

  • Since 2012, Research Assistant, Department of Evolutionary Biology and Environmental Studies – Population Ecology, University of Zürich, CH
  • 2010–2012, Research Assistant, Department of Evolutionary Biology and Environmental Studies – Sexual Selection and Speciation, University of Zürich, CH
  • 2008–2009, MQRES Fellow, Centre for the Integrative Study of Animal Behaviour, Macquarie University, Sydney, AUS
  • 2002–2008, Research Assistant, Institute of Zoology, University of Zürich, CH
  • 2000–2002, Temporary Employee, Koller Auctions Zürich, CH
  • 1994–2000, Studies in Biology, Diploma in Zoology, University of Zürich, CH
  • 1989–1994, Studies in Architecture, Swiss Federal Institute of Technology Zürich, CH

Stefan Sommer, our new rotifer meister

Many long-term studies on larger vertebrates provide us with only a single time series to study population dynamics. To test all the interesting hypotheses arising from these studies, we have to shrink those systems into tubes and replicate under different treatments. For this, with the invaluable help of Dr. Diego Fontaneto (Institute of Ecosystem Studies, Italy), we chose the rotifers as our experimental system. It didn’t take too long for us to realize that we needed expert help. And that help arrived as a swiss-army-knife of a guy: Stefan Sommers, our research associate, rotifer-meister, orchestrator of our microcosm lab!

Resurrecting population responses to past environmental changes from lake sediments

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Piero Guilizzoni from the Institute of Ecosystem Study during sediment sampling in 2012.

In this project, we investigate life-history responses of a freshwater rotifer, Brachionus calyciflorus, in retrospect. This is possible because brachionid rotifers produce dormant stages, so-called resting eggs, some of which remain viable in lake sediments for decades.

During the last century, Lake Orta – a deep, subalpine lake in northern Italy – was severely affected by industrial pollution. In 1926, a newly established textile factory began to discharge copper- and ammonium-sulphate contaminated sewage into the lake. The following acidification of the lake resulted in a dramatic decrease in rotifer diversity and an accumulation of resting eggs in the sediments. From the late 1950s onward, pre-treatment of the sewage prior to discharge gradually improved the quality of the lake water, and recovery was further accelerated by whole-lake liming in 1989 and 1990. Ten years after these liming efforts, the pH of Lake Orta had returned to pre-pollution levels, and copper was virtually absent from the water column.

In collaboration with the Institute of Ecosystem Study in Verbania, Italy, we collected sediment cores from different basins of Lake Orta. Back in the laboratory in Zürich, we screen these cores for brachionid resting eggs, which we try to hatch. Subsamples of rotifer lineages established from successfully hatched resting eggs are then subjected to a variety of treatments mimicking selected water parameters of historic lake conditions. Using such a ‘resurrection ecology’ approach allows us to investigate the adaptive value of life-history differences among rotifer lineages from different sediment layers, with each layer representing a distinct period in the well-documented pollution history of Lake Orta.

 

The video shows a B. calyciflorus female carrying five male eggs.

 

In collaboration with:

Predicting population responses to environmental change

species2A major goal in biodiversity conservation is to predict responses of biological populations to environmental change. To achieve this goal, we must identify early warning signals of the demographic changes that underlie sudden population declines or explosions. Some studies have achieved phenomenological prediction of sudden changes, but recent advances that link trait-based information with demography hint that a mechanistic understanding is within reach. We are developing a predictive framework by investigating how wildlife populations respond demographically, ecologically and evolutionarily to environmental change, and identifying the demographic and phenotypic statistics that can be used as early warning signals of population change. This project will exploit nine unique mammalian systems to identify early warning signals of population change and test these signals on two experimental systems. The results will hopefully provide much-needed predictive insight into how wildlife populations respond to rapid environmental change.

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In collaboration with: