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Predator-prey trait associations and feeding preferences of demersal fishes in the southern North Sea

Kim E. Ludwig*, Anja Singer, Ingrid Kröncke, Anne F. Sell

*Corresponding author:

ABSTRACT: In marine ecosystems under ongoing long-term changes, reducing complex food webs to their functionally important properties enables systematic analysis of bottom-up/ top-down regulations and species turnover. The assessment of feeding interactions in the form of predator- and prey trait associations provides a better understanding of predators’ criteria for prey selection and thus is a promising approach to reduce complexity. Here, we tested RLQ ordination and fourth-corner analysis, complementary multivariate approaches, as tools to identify ecologically relevant associations between the traits of eight demersal fish species in the southern North Sea and their fish or benthic prey. To scrutinize the trait-based results in their appropriateness to reflect selective feeding behaviour of the predator species, we compared them with the taxa-based electivity index Chesson’s α. Among seven predator traits investigated, body tissue composition represented by omega-3 polyunsaturated fatty acid (PUFA) content was significantly associated with prey traits, being positively correlated with energy density of the prey and negatively with prey of low mobility. Comparisons with the electivity indices showed that the prey preferred by predators corresponded relatively well with the identified prey trait preferences. The results of the tested analysis approach support its use when assessing the mutual dependences of predator- and prey populations on a functional level. Provided the data availability and quality of feeding-related traits is sufficiently high, trait-based predator-prey analysis with RLQ and fourth-corner analyses offers new possibilities for understanding food web dynamics in the context of climate change-induced species distribution shifts.