Individual contribution to niche expansion in amphibians: a test of the niche variation hypothesis

The niche variation hypothesis (NVH) suggests that populations released from competition are able to expand their realized ecological niche. This increase in total niche width (TNW) can arise by 1) increasing heterogeneity among individuals' niche through individual specialization, i.e. inter-individual variation in resource use, (IS) occurring when different individuals of a population use a subset of the population's resource pool, or 2) by expanding the niche of all individuals within the population. Although several morphological and phenotypical studies have confuted the NVH, there is generally strong support for this hypothesis when behavioural or ecological traits are considered, and in particular when the trophic niche is measured at the individual level. In this study our primary aim is to corroborate the NVH, providing robust evidence for a significant and positive relationship between population TNW and IS in amphibian populations, at a global scale.