The adaptive value of density-dependent habitat specialization and
social network centrality
Abstract
Density dependence is a fundamental ecological process. Patterns of
animal habitat selection and social behaviour are often
density-dependent and density-dependent traits should affect
reproduction and survival, and subsequently affect fitness and
population dynamics. The Ideal Free Distribution and Optimal Foraging
Theory present distinct predictions about how the effect of habitat
selection on fitness differs across a population density gradient. Using
a social ungulate (Rangifer tarandus) as a model system, we test
competing hypotheses about how (co)variance in habitat specialization,
social behaviour, and fitness vary across a population density gradient.
Within a behavioural reaction norm framework, we estimated
repeatability, phenotypic plasticity, and phenotypic covariance among
social behaviours and habitat selection to demonstrate the adaptive
value of these phenotypes across a population density gradient. In
support of Optimal Foraging Theory, but not the Ideal Free Distribution,
we found that at high density habitat specialists had higher fitness
than generalists, but were also less social than habitat generalists,
suggesting the possibility that specialists were inhibited from being
social. Our findings illustrate that social strength and habitat
specialization varied consistently among individuals across a density
gradient, but that habitat specialists maximized fitness at high
density. Taken together, our study provides preliminary support for
Optimal Foraging Theory as the driving mechanism for density-dependent
habitat specialization.