Weak cross‐species relationships between body size and trophic level belie powerful size‐based trophic structuring in fish communities

Abstract

Summary1. Body size determines rates of respiration and production, energy requirements, mortality rates, patterns of predation and vulnerability to mortality. Body size distributions are often used to describe structure and energy flux in communities and ecosystems. 2. If clear relationships can be established between body size and trophic level in fishes, they may provide a basis for integrating community and ecosystem analyses based on size spectra, food webs and life histories. 3. We investigated relationships between the body sizes (weight and length) of northeast Atlantic fishes and their trophic level. The abundance of 15 N, as determined by stable isotope analysis, was used as an index of trophic level. 4. Cross-species and comparative analyses demonstrated that body size was unrelated or weakly related to trophic level. Thus allometric relationships between body size and trophic level could not be used to predict the trophic structure of fish communities. 5.The results of the cross-species analyses contrasted with patterns in the size and trophic structure of entire fish communities. When fish communities were divided into size classes, there were strong positive relationships between size class and trophic level. The slope suggested a mean predator : prey body mass ratio of 80 : 1. 6. Our results suggest that body size does not provide a useful surrogate of trophic level for individual species, but that body size is an excellent predictor of trophic level within the community, providing an empirical basis for integrating community analyses based on models of trophic structure and body size distributions.

Size-selective fishing drives species composition in the Celtic Sea

“…Life-history parameters and trophic interactions between individuals are determined by individual body size and motivated by the observed strong sizedependence of life-history traits (Peters, 1983) and trophic level (Jennings et al, 2001(Jennings et al, , 2007 on body size. A model community consists of several maturation size classes of fish, with each size class representing all species with maturation sizes in the range [M mat ; M mat + DM mat ].…”

“…Conversely, if fishing alters size structure mainly through changing the biomass abundance of species, then species evenness and eventually composition will be affected, and long-term, possibly irreversible, community-scale effects can arise as Myers and Worm (2003) observed. As marine communities exhibit strong correlations between body size and trophic level (Cohen et al, 1993;Jennings et al, 2001Jennings et al, , 2007, changes in the size structure of fished communities may be used to indicate fisheries-induced strain in foodwebs (Rochet and Trenkel, 2003). Many size-based indicators (SBIs) have been proposed to quantify the effects of fishing on marine foodwebs, and they have been compared in several studies (e.g.…”

The paradox of inverted biomass pyramids in kelp forest fish communities

“…Recent work demonstrating the equivalence of biomass pyramids and biomass spectra highlights that, in size-structured assemblages, where trophic-level increases with body size, biomass distributions should be 'stacks' or bottom-heavy pyramids, and not strongly inverted [3]. Furthermore, natural history suggests that fish communities tend to be strongly size-structured because indeterminate growth and gape-limited size-selective predation predominate among fishes [5,6]. Hence, the empirical evidence of IBPs on reefs presents an interesting paradox.…”

Sete motivações teóricas para o uso da modelagem baseada no indivíduo em ecologia

“…Através do tamanho corporal, pode-se avaliar o risco de extinção de algumas espécies mesmo que pouco se conheça acerca de sua biologia, o que tem implicações práticas importantes para a conservação (De Marco, 1999). O tamanho corporal é também um poderoso preditor de relações tróficas (Cohen et al, 1993;Jennings et al, 2001;Woodward et al, 2005), o que facilita a construção de redes complexas e realistas de interações por meio de regras simples. Tais facilitadores permitem a construção de modelos para simular grandes números de espécies (Shin & Cury, 2001;van Nes et al, 2002;Mamedov & Udalov, 2002;Parrott & Kok, 2002), que podem inclusive auxiliar a investigar questões teóricas mais profundas como, por exemplo, a influência de características bionômicas sobre as regras de assembléia em comunidades naturais (Giacomini, 2006).…”