Testing the energy limitation hypothesis on desert brown food-webs

• Applicant: Professor Dr. Stefan Scheu
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560855412

Although Elton’s Energy Limitation Hypothesis (ELH) is nearly a century old, it is supported by very little evidence. The ELH is based on the idea that the height of a food-web depends on the energy available for the food-web at the basal level. Most of the studies on the ELH have been done in aquatic ecosystems and evidence in terrestrial ecosystems is lacking. It has also been claimed that body size is more significant in determining than energy, and body size of primary consumers is negatively correlated with an ecosystem’s available energy (primary productivity). The Size Limitation Hypothesis (SLH) is therefore an alternative to the ELH. Studies on ELH have used Food-Chain Length (FCL) to represent the food-web height to compare with available energy and were all conducted on “green food-webs” which are based on herbivores eating live plant material. The “brown food-web,” in which primary consumers consume dead organic material, has not been studied in regard to the ELH. Most brown food-webs are in the soil. Our project will test the ELH and the SLH on brown food-webs in soils by comparing FCL to available energy along a climatic gradient with sharply increasing available energy. FCL will be tested in desert soils in Israel along the rainfall gradient from Mediterranean to hyper-arid ecosystems. FCL will be assessed using bulk stable isotope analysis and compound-specific analysis of amino acids. The integration of two methods allows insight into the length of trophic chains and indicates how basal resources are channeled to higher trophic levels. To assess our result experimentally, we will add detritus to plots in the field and to lab microcosms with soils from sites along the climatic gradient. We will then measure the FCL and body size of arthropods in the soil to test whether the addition of energy changes the FCL. Our work will either strengthen the ELH or demonstrate variations on the theory, perhaps connecting it to body size of primary consumers. It will be the first work done on the ELH in soils and on brown food-webs. It will also be one of the first works assessing FCL on brown food-webs in desert soils.

• DFG Programme: Research Grants
• International Connection: Israel
• Partner Organisation: The Israel Science Foundation
• Cooperation Partner: Dr. Elli Groner