Revealing mechanisms of resource co-limitation in plankton at the community scale

• Applicant: Professor Dr. Alexander Wacker, since 4/2024
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449402474

The availability of resources in ecosystems is of paramount importance in structuring communities and food webs in nature. There is growing evidence that organisms or communities are often resource co-limited, i.e. their growth is limited simultaneously by multiple resources or nutrients. Primary producer communities are frequently co-limited by nitrogen (N) and phosphorus (P) in diverse ecosystems, shown by a positive synergistic response to experimental addition of N, P, and N&P. Primary producer biomass can also vary strongly in its elemental and biochemical composition depending on nutrient supply (e.g. N:P supply ratio) and community composition, resulting often in poor quality food for herbivorous consumers. Differences in the elemental and biochemical composition between primary producers and herbivores can constrain herbivore growth and the efficiency of energy transfer to higher trophic levels. Co-limitation of consumers has been observed mainly at the organismal level and very rarely in a community context. Hypothesized mechanisms that lead to co-limitation at the community level are still understudied. By using a quantitative literature survey and comprehensive laboratory and mesocosm experiments, the project aims to gain knowledge on co-limitation patterns of herbivorous consumers and how such patterns emerge in plankton communities. A meta-analysis shall identify in which systems and magnitude consumer co-limitation has been observed. Laboratory and mesocosm experiments will be used to investigate the mechanisms that lead to co-limitation patterns in primary producer communities and how co-limitation of primary producers translates into growth responses of herbivores via differences in food quantity and quality. Microcosm experiments with phytoplankton communities and different nutrient supply regimes will be used to investigate the underlying mechanisms proposed for community co-limitation. Other microcosm experiments will be used to examine the effects of primary producer co-limitation on herbivore growth under the aspect of food quantity and quality and whether the presence of a predator changes the potential (co-)limitation responses of herbivores. A mesocosm experiment with semi-natural plankton communities will be used to verify the predictions arising from the microcosm experiments as well as to gain additional insights into more natural systems. Elemental and fatty acid measurements of phytoplankton and zooplankton will accompany the experiments to assess if the difference between tissue concentrations of primary producers and herbivores can be used to predict patterns of consumer co-limitation. Expected results will improve our understanding how varying nutrient supply to communities affects herbivore growth responses through co-limitation of primary producers, which is important in predicting feedbacks between herbivores and primary producers, especially regarding environmental change and nutrient pollution.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Erik Sperfeld, until 4/2024