Community ecology group


 Group leader: Louis-Félix Bersier

 		           

An understanding of the structure and functioning of ecological communities is becoming paramount in face of the current biodiversity crisis and climatic change. There is an urgent need to unravel processes underlying community organisation. Large efforts have recently been devoted to explore the relationship between diversity and functioning of communities. Using a range of different research approaches such as modelling, meta-analyses, experiments and empirical observations we hope to gain closer insights from the level of ecosystems down to communities and populations. Our findings are expected to yield results both of fundamental and conservation relevance.

Spider community     
Biodiversity and community structure
In the face of landscape fragmentation and climate change, understanding the structure and functioning of ecological communities is becoming more and more important. A range of theories have been developed to study ecological assembly rules, but verification by field studies is largely lacking. We are making use of spider community composition to test the prediction of the “neutral theory” that in local communities the equilibrium species richness and relative species abundance distribution is a function of immigration. We also use published data on bird communities to explore predictions of the niche hierarchy model to deepen our understanding of the effect of competition on the relative abundances of species.
Wildflowerstrip
Metacommunities
Aiming to develop a “meta food-web” approach to better understand community organization in spatially-structured ecosystems, we are going to make use of sown wildflower strips. Over the last decade, these ecological compensations zones have been established in the matrix of our intensive agriculture to conserve biodiversity. Using a balanced incomplete block design we are assessing the effect of the interplay of multi-trophic interactions and plant diversity on ecosystem functioning. Our large scale field study will enable us to better understand the organisation and dynamics of metacommunities and the gained knowledge might help to improve current agri-environment schemes.         more
Food web  
Food webs
Qualitative food webs describe the feeding relationships between species in a biotic community. However, one of their major drawbacks is that all trophic interactions receive the same weight. To overcome this problem, food webs should be described and analyzed quantitatively. Up to now, we have a unique collection of 54 high quality quantitative webs from seven studies. We will use this dataset to test a range of stochastic models predicting the qualitative structure of food-webs. We further explore how phylogenetic and evolutionary constraints affect food-web structure. Our findings will be useful to assess to what extent species-level and system-level processes explain community organization. Our fundamental insight may improve our knowledge on the conservation of biodiversity.
Whinchat  
Conservation
The above projects tackle important issues in conservation biology. We are also interested in specific studies in conservation, mostly with birds. The Whinchat, Saxicola rubetra, is a small migratory passerine bird breeding in open rough pasture or similar uncultivated grassland. Even though the global population is not believed to approach the thresholds for IUCN Red List, it is an endangered species in Switzerland. The whinchat is widespread in the Alps, but uncommon on the Plateau. We are assessing biological factors such as predation pressure, feeding frequency and diet shifts as well as the energetic costs of foraging under different management scenarios of pastures and grasslands.
Food chain  
Dynamics of multitrophic systems in mesocosms
Using the simple tritrophic model system Scenedesmus gracilis (green algae) – Daphnia pulex (water flea) – Poecilia reticulata (guppy), we attempt to understand ecological processes such as plant palatability as a trigger of trophic cascades or the detection of population thresholds. This tritrophicmodel system is perfectly suited to answer these questions, easy to maintain and of disposal all-the-year. It is also a perfect playground for students. 
    Model of functional response
Modelling

Modelling plays an important role in most above research topics. More specifically, we are developing stochastic models for the dynamics of trophic interactions. We started with simple functional responses (the number of prey eaten per predator) modelled as pure death process (density of predators is constant). We will use existing experimental data and mesocosms results to test these models. We plan to enlarge the scale of these models to tritrophic systems and ultimately to whole communities. We believe that stochastic models are inherently more adequate to explore complexity-stability relationships than classical differential equations. These modelling projects are collaboration with the Department of mathematics in Fribourg, the Statistic chair of the EPFL and the NCCR Plant survival.