Abstract Gape size is a key functional trait that influences feeding performance and ecological fitness across animal taxa; yet, its role within species remains underexplored, particularly in dynamic environments. We investigated the relationship between relative gape size and condition factor ( Kn ) across 15 species of tropical freshwater fish from northern Australia, spanning four trophic groups: predators, micro-carnivores, omnivores, and herbivores/detritivores. Using linear mixed-effects modelling, we assessed how this relationship varies across trophic groups and seasonal hydrology. Our results revealed a strong positive association where larger gape sizes were associated with enhanced body condition in predators and, to a lesser extent, micro-carnivores—especially during the mid- and late-dry seasons when resource availability is reduced. In contrast, this relationship was weak or absent in omnivores and herbivores/detritivores, whose diets are less likely to be gape-limited. These findings suggest that the functional benefits of larger gape sizes are context-dependent, conferring greater fitness advantages to carnivorous species under seasonal resource limitation than to other trophic groups. Our study highlights the need to consider both trophic ecology and seasonal variability in resource availability regimes when linking traits to performance and provides empirical support for the context-dependent utility of gape size as a functional trait in ecological research.
Luiz et al. (Thu,) studied this question.