Food web ecology

Head of the working group: Dr. Mario Brauns

Nahrungsnetzökologie Human activities have been and are continuing to alter stream and river ecosystems worldwide. Most of these alterations have dramatic consequences for biological communities as physical, chemical and habitat characteristics are simultaneously affected. The assessment of the associated ecological effects requires whole-ecosystem approaches as they have the potential to detect common responses of ecosystem functioning to human-driven alterations independent of the geographic region or climate zone. Here, freshwater food webs and their response to human perturbations are advantageous over traditional approaches as food webs integrate information from producer to higher level consumers as well as their trophic interactions.

Our research focuses on the study of food web topology and consumer-resource interactions in stream and river ecosystems. We are interested in how these systems function and how human perturbations affect their functional characteristics. Building on that, we are working on indicators to assess the functional status and to inform catchment management on how to mitigate human impacts on ecosystem matter cycling. Our work involves a significant field component, including large-scale as well as field mesocosm studies using the MOBICOS facilities. We use a range of techniques but primarily combine stable isotopes, mixing model analysis and estimates of ecosystem productivity and respiration to quantify organic matter fluxes.


Current projects

2012-2015

Homogenisation of ecosystem functioning between temperate and Neotropical streams due to agricultural land use (HECTARE)

Hectare


The expansion and intensification of agricultural areas and the associated deforestation, eutrophication and modification of habitat heterogeneity remain the most important stressors to stream ecosystem functioning worldwide. The alteration of key environmental characteristics may cause the loss of functional attributes specific for streams in different climate zones and may ultimately lead to a homogenisation of stream ecosystem functioning. Previous studies were mostly restricted to a single function in a particular biome and a thorough understanding on the potential for an agriculturally driven functional homogenisation of stream ecosystems among climate zones is lacking. The project HECTARE analyses ecosystem functioning of pristine and agricultural streams situated in the German Harz and in the Brazilian Cerrado and Atlantic forest. By the novel combination of quantification of food webs and measurements of ecosystem productivity and respiration, HECTARE delivers a mechanistic understanding on energy- and matter fluxes in temperate and Neotropical streams including their trophic coupling to the catchments. Building on that, key pathways of whole-ecosystem matter and energy fluxes that are impacted by agricultural land use will be identified. The inter-biome approach proposed with HECTARE will allow for a synthesis of impact patterns associated with agricultural land use and an analysis of the degree of functional homogenisation of stream ecosystems.

Funded by Deutsche Forschungsgemeinschaft DFG (Grant no. BR 4358/1-1)


2010-2013

Does shoreline protection at the river Elbe control the structure of food webs and the trophic base of secondary production?

 

Groyne field at the River Elbe

Basically all sections of large, navigable rivers in Germany are morphologically characterized by various types of shoreline protection primarily built to protect the river bank against erosion. These protection structures increase the flow velocity in the main channel thereby changing natural sediment dynamics along the transversal dimension of the river. While in the main channel transport of sand waves and dunes are promoted, sedimentation close to the river banks increases. Previous studies demonstrated that biodiversity and abundances of macroinvertebrates at the River Elbe are determined by the type of shoreline protection. However, a mechanistic understanding on how their morphology affects functional properties of the macroinvertebrate community and thus ecosystem functioning of large rivers is virtually lacking. With this project we address the following research questions: 

  1. Does food web topology depend on the type of shoreline protection?
  2. Does shoreline protection affect the flow of organic matter in benthic food webs?
  3. Is phytoplankton retention in benthic food webs controlled by the type of shoreline protection?


2010-2013 

Effect of terrestrial carbon on the resilience of lakes (TERRALAC)


Team


Collaboration

  • Brandenburg University of Technology (Germany)
  • Catalan Institute for Water Research (Spain)
  • Federal University of São João del-Rei (Brazil)
  • Leibniz-Institute of Freshwater Ecology and Inland Fisheries (Germany)
  • National Environmental Research Institute (Denmark)
  • University of Cologne (Germany)
  • University of Koblenz-Landau (Germany)