Data from: Multilevel and sex-specific selection on competitive traits in North American red squirrels.

Individuals often interact more closely with some members of the
population (e.g. offspring, siblings or group members) than they do with
other individuals. This structuring of interactions can lead to multilevel
natural selection, where traits expressed at the group-level influence
fitness alongside individual-level traits. Such multilevel selection can
alter evolutionary trajectories, yet is rarely quantified in the wild,
especially for species that do not interact in clearly demarcated groups.
We quantified multilevel natural selection on two traits, postnatal growth
rate and birth date, in a population of North American red squirrels
(Tamiasciurus hudsonicus). The strongest level of selection was typically
within-acoustic social neighbourhoods (within 130m of the nest), where
growing faster and being born earlier than nearby litters was key, while
selection on growth rate was also apparent both within-litters and
within-study areas. Higher population densities increased the strength of
selection for earlier breeding, but did not influence selection on growth
rates. Females experienced especially strong selection on growth rate at
the within-litter level, possibly linked to the biased bequeathal of the
maternal territory to daughters. Our results demonstrate the importance of
considering multilevel and sex-specific selection in wild species,
including those that are territorial and sexually monomorphic.