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The slow–fast continuum is a commonly used framework to describe variation in life-history strategies across species. Individual life histories have also been assumed to follow a similar pattern, especially in the pace-of-life syndrome literature. However, whether a slow–fast continuum commonly explains life-history variation among individuals within a population remains unclear. Here, we formally tested for the presence of a slow–fast continuum of life histories both within populations and across species using detailed long-term individual-based demographic data for 17 bird and mammal species with markedly different life histories. We estimated adult lifespan, age at first reproduction, annual breeding frequency, and annual fecundity, and identified the main axes of life-history variation using principal component analyses. Across species, we retrieved the slow–fast continuum as the main axis of life-history variation. However, within populations, the patterns of individual life-history variation did not align with a slow–fast continuum in any species. Thus, a continuum ranking individuals from slow to fast living is unlikely to shape individual differences in life histories within populations. Rather, individual life-history variation is likely idiosyncratic across species, potentially because of processes such as stochasticity, density dependence, and individual differences in resource acquisition that affect species differently and generate non-generalizable patterns across species. 

Light pollution is increasing worldwide and significantly affects animal behavior. In birds, these effects include advancement of morning activity and onset of dawn song, which may affect extra‐pair paternity. Advanced dawn song of males may stimulate females to engage in extra‐pair copulations, and the earlier activity onset may affect the males’ mate guarding behavior. Earlier work showed an effect of light at night on extra‐pair behavior, but this was in an area with other anthropogenic disturbances. Here, we present a two‐year experimental study on effects of light at night on extra‐pair paternity of great tits (Parus major). Previously dark natural areas were illuminated with white, red, and green LED lamps and compared to a dark control. In 2014, the proportion of extra‐pair young in broods increased with distance to the red and white lamps (i.e., at lower light intensities), but decreased with distance to the poles in the dark control. In 2013, we found no effects on the proportion of extra‐pair young. The total number of offspring sired by a male was unaffected by artificial light at night in both years, suggesting that potential changes in female fidelity in pairs breeding close to white and red light did not translate into fitness benefits for the males of these pairs. Artificial light at night might disrupt the natural patterns of extra‐pair paternity, possibly negates potential benefits of extra‐pair copulations and thus could alter sexual selection processes in wild birds.