Linking size‐based trophodynamics and morphological traits in marine fishes

Abstract

The rule of thumb in marine trophodynamics indicates that the bigger an organism, the higher its trophic level (TROPH). This generalization leads to the assumption that fishes increase their TROPH with growth. However, a recent review showed that for many species, TROPH does not increase with body size, suggesting that size‐independent feeding is not rare in marine fishes. Here, we assessed some morphological traits of marine fishes that could potentially be used as indicators for the ability to vary TROPH with body size. Stable isotope values of nitrogen were used as a proxy TROPH. The specific objectives were as follows: (a) to evaluate the relationship between the oral gape and the trophodynamic trend and (b) to quantify the relevance of 11 external morphological traits in determining the size‐based trophodynamics. We used random forest models to identify the morphological traits that would help predict which species would have the potential to increase TROPH with growth and which would have not. The selected traits included the pelvic fin relative position, the dorsal fin shape, total length, and relative mouth size. Our results also showed a marked relationship between the rate of increase in the oral gape and TROPH. The analyses presented here provide the first comprehensive and quantitative review aiming at linking the trophodynamics of marine fishes with external morphological traits.

Foraging habitat determines predator–prey size relationships in marine fishes

“…The trophic‐level information in Ríos et al . (2019) is consistent with the habitat‐prey size effects reported earlier. Significantly more benthic/benthopelagic fishes showed intraspecific increases in trophic level as they grew than pelagic species [98% ( n = 84), 79% ( n = 19) respectively, χ 2 = 9.85, P < 0.01), suggesting that prey size increases are more likely in benthic predators.…”

“…The PPS analyses are based on a small number of species, but trophic‐level information (which correlates with body size, Romanuk et al ., 2011), for additional species from Ríos et al . (2019)(their “reliable” quality data from their Supporting Information Table S1), was used to examine whether intraspecific trophic‐level‐predator size trends varied with habitat.…”

Fish stable isotope community structure of a Bahamian coral reef

“…In aquatic systems, large individuals generally feed at higher TPs (Jennings et al 2001(Jennings et al , 2002bAl-Habsi et al 2008;Romanuk et al 2011). This is a result of ontogenetic dietary shifts, morphometric changes including increasing gape size, post-maturity factors and greater predator ability that influence foraging (Peters 1986;Jennings et al 2001;Munday 2001;Jennings et al 2002b;Al-Habsi et al 2008;Newman et al 2012;Robinson and Baum 2015;Ríos et al 2019). However, some large fishes forage at lower TPs due to dietary shifts (e.g.…”

Ontogenetic diet shifts of rough scad Trachurus lathami in the North Patagonian shelf (south‐west Atlantic Ocean)

“…However, TL was slightly higher in the size range 160–190 mm L , matching the preference for misidaceans, prey that exhibits elevated TL values due to their feeding behaviours (Horn et al ., 2013). A recent review showed that for many species, the trophic level does not increase with body size, suggesting that size‐independent feeding is not rare in marine fishes (Galván et al ., 2010; Ríos et al ., 2019). Predators may rapidly change their trophic niche, therefore changing the whole configuration of the web, to adapt for different prey abundance and availability.…”