Relative heart size and fish foraging ecology in a lake food web

Abstract

Organisms occupying high trophic positions in food webs are proposed to exert a stabilizing effect on ecosystems under changing conditions. A possible mechanism underlying this phenomenon is higher mobility of large-bodied predators, which allows broad spatial scale foraging across habitats. If top predators foraging flexibly across habitats display an enhanced capacity for mobility, they should have increased blood circulation requirements compared with other organisms in a food web. Blood circulation capacity can be estimated from the relative size of the heart ventricle, the muscle mass that powers the cardiac pump. We sampled wild teleost fish in a freshwater lake food web to investigate the relationship between relative heart ventricle size and individual measures of trophic position, energy channel use (littoral versus pelagic), and foraging flexibility (coupling) estimated from 15N and 13C stable isotope signatures. The results showed that relative ventricle size is associated with increased relative trophic position and decreased use of littoral carbon across species, but not within species, in this system. The foraging flexibility required for coupling was not associated with heart ventricle size.