DOI: 10.5061/dryad.92rv6bq
title: Data from: Integrating fitness components reveals that survival costs outweigh other benefits and costs of group living in two closely related species

description: Group living can be beneficial when individuals reproduce or survive
 better in the presence of others, but simultaneously there might be costs
 due to competition for resources. Positive and negative effects on various
 fitness components might thus counteract each other, so integration is
 essential to determine their overall effect. Here, we investigated how an
 integrated fitness measure (reproductive values; RV) based on six fitness
 components varied with group size among group members in
 cooperatively-breeding red-winged and superb fairy-wrens (Malurus elegans
 and M. cyaneus). Despite life historie differences between the species,
 patterns of RVs were similar, suggesting that the same behavioural
 mechanisms are important. Group living reduced RVs for dominant males, but
 for other group members this was only true in large groups. Decomposition
 analyses showed that our integrated fitness proxy was most strongly
 affected by group size effects on survival, which was amplified through
 carry-over effects between years. Our study shows that integrative
 consideration of fitness components and subsequent decomposition analysis
 provide much needed insights into the key behavioural mechanisms shaping
 the costs and benefits of group living. Such attribution is crucial if we
 are to synthesize the relative importance of the myriad group size costs
 and benefits currently reported in the literature.
description: FairyWrenDataThe aim here is to quantify the effect of the group size an individual experiences in a given year on an integrative measure of fitness in two closely related fairy-wrens (Malurus elegans and M. cyaneus). Here, we combine six separate fitness components into one aggregate fitness proxy, using the concept of reproductive value. RV describes the expected contribution by individuals of a given age- or stage-class (here group size, sex and social status) to the future long-term growth of a population. We determined six fitness components: group productivity (number of fledglings produced per group per breeding season); within-group parentage (probability of paternity/maternity within own group); extra-group paternity (number of offspring sired by male in other social group); offspring sex-ratio; juvenile and adult survival; probability of obtaining dominant status; and the probability of increasing/decreasing the group size in the next year. Reproduction was split up into a within- and extra-group parentage component, as group members can parasitize the reproductive success of the dominant breeding pair. These six fitness components were integrated using reproductive values (RVs). RVs were calculated from population matrices, which were derived from a life cycle model. The next step was then to translate our life-cycle graph into a matrix population model, in which the matrix elements consist of the six fitness components in which we are interested. We used the statistical model estimates of each fitness component derived from the field data as input to the projection matrix, which allows—using standard matrix algebra— calculating the RVs of individuals as a function of their status, sex and group size.