Diet-consumer interactions under variable stressor conditions as revealed by stable isotope studies of individual amino acids
The analysis of food webs allows for detailed conclusions on diet-consumer interactions as well as the origin of resources in ecosystems. We will use food webs derived from compound specific stable isotope analysis (CSIA) of amino acids (AAs) to unravel species’ niches and trophic links between species under conditions of multiple stressor increase and release, thus allowing closer insight into ecosystem structures and functions characterizing response to degradation and recovery. During the first phase we will contribute to test Main Hypothesis MH2 and MH3 of RESIST by investigating the following Specific Hypothesis (SH): (i) Hydromorphological stressors will mainly change the isotope values of non-essential and trophic amino acids in higher organisms, while stressors affecting water quality will also impact isotope values of essential and source amino acids and reflect changes in community composition of primary producers (SH A13-1). (ii) Complex food webs can only recover if a variety of food sources has been re-established (SH A13-2). (iii) Heteroxenous parasites indicate the complexity of aquatic food webs as revealed by CSIA under recovery conditions, while monoxenous parasites can also strive on degraded sites (SH A13-3).
The fundamental assumption is that multiple stressor increase and release will result in dynamic changes of resource utilisation and diet-consumer interactions that can be probed with CSIA. We particularly expect a simplification of food webs with fewer trophic levels under stress conditions that should be reflected in δ15N of trophic and source AAs. In addition, δ13C analysis of essential and non-essential AAs will reveal changes in food sources due to ecological degradation and during recovery. We will test these assumptions on a temporal and spatial scale of the Emscher/Boye catchment, where a recovery gradient from severe pollution and hydromorphological degradation exists. Whereas other projects will focus on bulk stable isotope analysis, we will complement these data because CSIA can reveal changes in stable isotope compositions that might be disguised in the averaging bulk measurement.
We will closely cooperate with A09, A11 and A12 to elucidate food web complexities and changes in the higher trophic hierarchies of macroinvertebrates, fish and parasites under stressor and recovery conditions. Although the refined analytical methods aim at the measurement of many individual AAs in order to facilitate data interpretation, primary focus will be on phenylalanine and glutamic acid as representatives of source and trophic AAs, respectively, that have been utilised as proxies for the determination of trophic positions in the past. We expect to gain deeper insight into riverine food web structure and their spatial-temporal dynamics as compared to more traditional ways of food web analysis.