•Personality structure systematically varies across 16 large population samples.•Niche diversity and wealth effects show credible effects on personality structure.•Acute population-level threats due to COVID-19 do not show credible effects.•Life expectancy showed the most consistent results, suggesting new avenues for improving theorizing about niche effects on personality structure. We report systematic variability in the psychometric properties of a brief personality inventory during the early stages of the COVID-19 pandemic. Drawing upon recent discussions about the universality vs cultural relativism of personality measures, we review and comparatively test theories predicting systematic variability in personality measurement across cultures using an established brief personality measure applied to population samples in 16 nations during the first wave of the COVID-19 pandemic (N = 35,052). We found systematic variation in factor replicability and effective dimensionality. In line with previous theorizing, factors replicated better in contexts with greater niche diversity. Examining possible drivers underlying this association, the investigation of the individual components in the niche construction index suggested that life expectancy and to a lesser degree economic complexity are associated with greater personality structure differentiation. Population-level indicators of acute threat due to COVID-19 did not show credible effects. These patterns suggest that a) investigation of personality structure in population samples can provide useful insights into personality dynamics, b) socioecological factors have a systematic impact on survey responses, but c) we also need better theorizing and research about both personality and culture to understand how niche construction dynamics operate. Display omitted