Food webs: Scaling from the individuals to ecosystems

An important goal for ecologists is to identify mechanisms that operate via selection at the individual level, but which explain patterns and processes at higher levels of organisation (populations, communities, ecosystems).  Body size is a characteristic of individuals that is correlated with an array of physical, physiological and behavioural traits, all of which can produce emergent properties in food webs.  Unfortunately, even within the small sample of high quality food webs currently available, few include body size data and fewer still contain information at the individual level, which is the scale at which trophic interactions actually occur: almost the all food webs that have been constructed to date are based on ‘species-averaged’ data.  We demonstrate, using data from highly resolved food webs, how this can obscure the true nature of trophic interactions between individuals. Because of this artefact many current food web models are potentially undermined by species-averaging effects, and individual-based approaches, particularly those that can address ontogenetic and seasonal shifts offer better insight into reality.