Trophic niche-space imaging, using resource and consumer traits

Abstract

The strength of trophic (feeding) links between two species depends on the traits of both the consumer and the resource. But which traits of consumer and resource have to be measured to predict link strengths, and how many? A novel theoretical framework for systematically determining trophic traits from empirical data was recently proposed. Here we demonstrate this approach for a group of 14 consumer fish species (Labeobarbus spp., Cyprinidae) and 11 aquatic resource categories coexisting in Lake Tana in northern Ethiopia, analysing large sets of phenotypic consumer and resource traits with known roles in feeding ecology. We systematically reconstruct structure and geometry of trophic niche space, in which link strengths are predicted by the distances between consumers and resources. These distances are then represented graphically resulting in an image of trophic niche space and its occupancy. We find trophic niche to be multidimensional. Among the models we analysed, one with two resource and two consumer traits had the highest predictive power for link strength. Results further suggest that trophic niche space has a pseudo-Euclidean geometry, meaning that link strength decays with distance in some dimensions of trophic niche space, while it increases with distance in other dimensions. Our analysis not only informs theory and modelling but may also be helpful for predicting trophic link strengths for pairs of other, similar species.