“TippingPond" (2013-2016)

funded by: BMBF through EU Biodiversa programme

Ponds and shallow lakes have played a key role in the development of theory on regime shifts in ecosystems, where resilience to environmental change is broken when a threshold disturbance is surpassed. Upon eutrophication or with temperature increase, ponds and lakes may shift from a clearwater to a turbid state with an associated decline in biodiversity and ecosystem services. Small inland waters are very important for regional biodiversity and, due to their high number, have an important contribution to ecosystem services such as carbon storage. Ponds are very convenient model systems for ecological studies, being numerous and relatively easy to monitor and manipulate. We here capitalize on these assets and the available ecological knowledge on ponds and lakes to engage in a combined survey and manipulative study to identify (1) the link between extant biodiversity and resilience to disturbance in natural systems and (2) early warning signs of regime shifts that may cause a strong decline in ecosystem services.

Involved: Laura Verbeek, Maren Striebel, Helmut Hillebrand

Collaboration with: Luc de Meester (KU Leuven, Belgium), Silke Langenheder & Eva Lindström (Uppsala University, SE), Alexander Wezel (ISARA Lyon, FR)

“ELSER” EcoLogical Stoichiometry in aquatic food webs (2009-2012)

funded by: DFG Hi 848/7-1 (in Cooperation with AWI/BAH, DFG Ma4501/1-1)

The ecological stoichiometry theory has been successful in enhancing our understanding of trophic interactions between consumer and prey species. Consumer and prey dynamics depend on the nutrient composition of the prey relative to the nutrient demand of the consumer. However, most experiments on this topic used a single consumer species and very simple prey communities. Therefore, little is known about the validity of stoichiometric constraints on trophic interactions in more natural food webs. This project seeks to enhance our understanding of nutritional constraints in marine pelagic food webs by testing the consumer’s ability to select high quality food, by addressing the importance of food quality in multispecies zooplankton-phytoplankton interactions and by investigating the propagation of different phytoplankton quality via herbivores to predatory zooplankton and fish larvae. These aspects will be experimentally analysed in microcosms and mesocosms and fundamentally enhance our ability to predict the consequences of anthropogenically altered biogeochemistry in coastal waters on trophic transfer in ecosystems.

Involved scientists: Helmut Hillebrand, N.N.

Collaborators:Arne Malzahn, Maarten Boersma, Cedric Meunier (Alfred Wegener Institut, Helgoland)

Nutritional bioindicators and ecological stoichiometry

funded by: Alexander von Humboldt-Stiftung (3.1-KAN/1139289 STP)

Involved: Paul C. Frost, Helmut Hillebrand

Relevance of functional diversity in microbial food webs: effects of grazer diversity on prey diversity and composition (2008-2011)

Funded by: DFG Mo 1931/1-1

Biodiversity studies are a major focus in ecological research due to the increasing species loss through anthropogenic impacts and environmental changes. Multitrophic effects, however, have only been analysed recently. In this project, the relevance of functional diversity will be investigated in microbial food webs. Consumer diversity and composition (generalists and specialists) will be manipulated in microbial microcosms in the laboratory and in mesocosms in a small lake (Accumer See, Schortens, Niedersachsen) to investigate the effect on prey diversity and composition (artificially assembled prey in the laboratory, natural prey community in lake mesocosms). This research question has neither been investigated experimentally so far with complex natural communities nor with differently specialized consumers and will therefore considerably enhance our understanding of multitrophic biodiversity effects. Furthermore, diversity will be analysed with rDNA based molecular methods, allowing to determine the genetic diversity in addition to the morphological diversity of the prey community.

Involved: Stefanie Moorthi, Joanna Filip, Helmut Hillebrand 

Cooperation with: Ulrike.-G. Berninger und Steve Wickham, Universität Salzburg (A), David A. Caron, University of Southern California, USA

Resilience and diversity in aquatic metacommunities: Effects of dispersal and the spatial scale of disturbance (2009-2012)

funded by: DFG Hi 848/8-1

Recent years have seen stringent advances in the analysis of spatial ecological dynamics embedded in the concept of metacommunities, in which species coexistence is mediated by local interactions and regional dispersal. However, we lack information on how metacommunity dynamics alter responses of diversity and resilience to disturbance and environmental fluctuations, especially if these disturbances differ in their spatial extent. To test this idea, we will establish experimental metacommunities consisting of connected microcosms inhabited by phytoplankton (and their consumers). The metacommunities differ in their dispersal rates (which affect regional and local diversity) and their coexistence mechanism (patch dynamics versus source-sink dynamics). In these communities, we will alter mortality by removing biomass in local or regional extent and measure the recovery of community composition and important ecosystem functions (primary production, nutrient retention) after this disturbance. We except resilience to be a function of dispersal rate, local richness and regional richness, but we expect different relative importance of these factors at different spatial scales of mortality. In a second set of experiments, we will address the importance of spatial coexistence for the stability of ecosystem processes over time under undisturbed but fluctuating environmental conditions. The results from this project will allow addressing the importance of spatial insurance mechanisms in fragmented landscapes in cases of habitat destruction, which are considered to be major causes of biodiversity loss in future environments.

Involviert: Helmut Hillebrand, Nils Gülzow

Kooperation mit: Birte Matthiessen, IfM-GEOMAR Kiel; Bradley J. Cardinale, Univ. Michigan (USA)

Temporal and SPATIAL TURNOVER IN phytoplankton communities (2008-2011)

funded by start-up money

This projects combines observational and experimetnal approaches to test the factors regulating spatial and temporal turnover of plankton spcies composition. We will use a field survey and experimental metacommunities to address changes in species composition across spatial, temporal and environmental gradients.

Involved: Helmut Hillebrand, Sandra Meier

Collaboration: Dr. Janne Soininen, University of Helsinki (FI)

Role of light for consumer-dynamics and nutrient turnover in microbial food webs of the marine pelagial (2010-2013)

Involved: Robert Ptacnik, N.N.

Collaboration: Prof. Tom Andersen, Univ. of Oslo, Norway, and Prof. Herwig Stibor, IUEM, Technopôle Brest-Iroise, France

funded by: EU Mesoaqua

Pigmented grazers (‘mixotrophs’) contribute significantly to microbial grazing, especially in oligotrophic lakes and oceans. Recent studies show that the bulk of bacterivory in the ‘blue ocean’ can in fact be attributed to pigmented grazers. The type of grazing (mixotrophy vs. heterotrophy) is expected to have major implications on the resulting remineralisation rates of nutrients in the microbial food web. Heterotrophic protists are limited by the amount of energy in their prey, and function as net-remineralizers in the food web (Azam et al. 1983). Conversely, mixotrophs may cover their energy demand by light and utilize all nutrients ingested with their prey for synthesis of new biomass. However, the competitive edge of mixotrophs over their heterotrophic competitors is bound to the availability of light. We thus hypothesize that light is a major agent in determining the relative importance of mixotrophic vs. heterotrophic grazing, and hence the relative nutrient regeneration rates within microbial food webs. We will test this hypothesis in a mesocosm experiment at the HCMR facility, where the natural plankton community will be exposed to a light gradient. The experimental design includes tracer studies for measurement of nutrient regeneration rates, molecular probes for the identification of the picoplankton and estimation of grazing rates, and specific measurement of photosynthetic yield. Finally, by relating zooplankton growth to seston stoichiometry, we also aim at testing the L:N hypothesis in this ultra-oligotrophic environment.

Involved: Robert Ptacnik, Stefanie Moorthi, Radka Ptacnikova

Collaboration: Paraskevi Pitta at Hellenic Centre for Marine Research (HCMR), Maren Striebel (WasserCluster Lunz, A)