Resource partitioning by Lake Tana barbs predicted from fish morphometricsand prey characteristics

We develop a food-fish model (FFM), which quantitatively relates properties of aquatic food types (size, shape, escape velocity, habitat, mechanical p roperties and chemical quality) to feeding structures of cyprinid fish. The model is based on functional morphology and experiments on search, capture , selection, and internal processing of food by fish. The FFM shows which f ood properties are most critical in feeding and how fish can optimise copin g with them. Relative food size imposes the highest demands, followed by pr ey velocity, food habitat and mechanical properties. These overrule taxonom ic affinities of food types. Highly demanding food types (large, fast prey, suspensions of plankton, benthic prey and mechanically tough items) impose incompatible morphological requirements on fish. We apply the FFM to the e ndemic Barbus species flock of Lake Tana (Ethiopia), since the structural d iversity of its 14 species reflects recent adaptations to trophic niches. W e predict their potentials in utilising different food types by quantitativ e comparisons of 35 parameters, measured for each species, with the values for each food specialist derived from the FFM. These diet predictions are t ested against gut contents from 4,711 fish, sampled over seasons and habita ts. Gut contents and predictions show a good overall fit. The value of the model is shown by its resolution in predicting resource partitioning among the barbs. For the 14 barbs a trophic hierarchy with six major trophic grou ps is reconstructed which closely matches the predictions. Trophic speciali sts (> 65% by volume of a single food type) are also structurally specialis ed, whereas less extreme anatomical structures characterise trophic general ists, allowing them to switch between feeding modes. Trophic generalists ar e best defined by behavioral flexibility, since feeding modes integrate bot h fish and food characters. The FFM is of practical use in evaluating the r ole of morphological diversity in an ecosystem and enables the analysis of trophic interactions in fish communities and of the cascading effects by en vironmental change. Such an approach can be instrumental in the development of management strategies for fisheries and in conservation of biodiversity .