Data from: Dietary niche variation and its relationship to lizard population density

(1) Insular species are predicted to broaden their niches, in response to
having fewer competitors. They can thus exploit a greater proportion of
the resource spectrum. In turn, broader niches are hypothesized to
facilitate (or be a consequence of) increased population densities. (2) We
tested whether insular lizards have broader dietary niches than mainland
species, how it relates to competitor and predator richness, and the
nature of the relationship between population density and dietary niche
breadth. (3) We collected population density and dietary niche breadth
data for 36 insular and 59 mainland lizard species, and estimated
competitor and predator richness at the localities where diet data were
collected. We estimated dietary niche shift by comparing island species to
their mainland relatives. We controlled for phylogenetic relatedness, body
mass, and the size of the plots over which densities were estimated. (4)
We found that island and mainland species had similar niche breadths.
Dietary niche breadth was unrelated to competitor and predator richness,
on both islands and the mainland. Population density was unrelated to
dietary niche breadth across island and mainland populations. (5) Our
results indicate that dietary generalism is not an effective way of
increasing population density nor is it result of lower competitive
pressure. A lower variety of resources on islands may prevent insular
animals from increasing their niche breadths even in the face of few
competitors.