Individual‐level diet variation in four species of Brazilian frogs

Abstract

Summary 1.Many natural populations exploiting a wide range of resources are actually composed of relatively specialized individuals. 2. This interindividual variation is thought to be a consequence of the invasion of 'empty' niches in depauperate communities, generally in temperate regions. If individual niches are constrained by functional trade-offs, the expansion of the population niche is only achieved by an increase in interindividual variation, consistent with the 'niche variation hypothesis'. 3. According to this hypothesis, we should not expect interindividual variation in species belonging to highly diverse, packed communities. 4. In the present study, we measured the degree of interindividual diet variation in four species of frogs of the highly diverse Brazilian Cerrado, using both gut contents and δ 13 C stable isotopes. 5. We found evidence of significant diet variation in the four species, indicating that this phenomenon is not restricted to depauperate communities in temperate regions. 6. The lack of correlations between the frogs' morphology and diet indicate that trade-offs do not depend on the morphological characters measured here and are probably not biomechanical. The nature of the trade-offs remains unknown, but are likely to be cognitive or physiological. 7. Finally, we found a positive correlation between the population niche width and the degree of diet variation, but a null model showed that this correlation can be generated by individuals sampling randomly from a common set of resources. Therefore, albeit consistent with, our results cannot be taken as evidence in favour of the niche variation hypothesis.

Trophic specialization at the individual level in a terrestrial generalist salamander

“…However, for a long time, at least in the case of amphibians, the individual contribution to the population trophic niche variation has remained largely unexplored. Recent reviews by Araújo et al (2009Araújo et al ( , 2011 and Bolnick et al (2003Bolnick et al ( , 2007 demonstrated that several temperate and tropical amphibian populations are indeed composed of a significant number of specialized individuals. This intrapopulation differentiation may become more intense when different prey types concentrate in different spatial patches where predators possessing different morphologies are attracted, or where behavioural or physiological adaptations are selected.…”

“…In amphibians, ontogenetic, morphological, and seasonal variations in individual trophic specialization have been described only recently and in a small number of species (e.g., Collins et al 1993;Maret and Collins 1997;Maerz et al 2006;Araújo et al 2009;da Rosa et al 2011;Schriever and Williams 2013). However, understanding the contribution of individual trophic specialization may allow for better understanding of population realized trophic niche and its contribution to the ecological food web, especially in those species that connect freshwater and terrestrial ecosystems (i.e., Regester et al 2006) or in populations that play a relevant role in energy storage and turnover in the litter of forest ecosystems (reviewed in Davic and Welsh 2004).…”

Upscaling the niche variation hypothesis from the intra- to the inter-specific level

“…Such a positive relationship between niche width and the level of individual heterogeneity is supported in taxa as diverse as gasteropods, fish, amphibians, or reptiles ). This relationship could, however, also be extended to the inter-specific level (Araújo et al , 2009; the level of individual heterogeneity in terms of niche width is expected to be larger in generalist species than in specialist species. Indeed, specialist species may be constrained by cognitive, physiological or morphological adaptations imposing a limit to inter-individual variation (Bolnick et al 2003).…”

The Influence of Body Size on the Ecology of Coastal Fish Predators in The Bahamas

“…Since frogs grow substantially after metamorphosis to reach adult size, they could be expected to experience considerable diet shifts during the terrestrial phase of their life cycle, but this was not found to be the case here. Stomach content analysis supported the isotope findings by showing that both juvenile and adult E. nattereri tend to specialize on ants and termites (Araujo et al 2009). …”