Latitude shapes diel patterns in insect biodiversity

The writings of naturalists from two centuries past are brimming with accounts of the stark differences in the kinds and numbers of organisms encountered during the day and night as well as between the tropical and temperate zones. However, only recently have ecologists begun to systematically explore the geographic variation in the diel activity patterns of species on Earth. Examining data from 60 insect communities distributed globally, I find that the proportion of nocturnal species in a community declines from a peak of 36% at the equator to 8% at 60° latitude, while the proportion of diurnal species shows no significant trend. By contrast, the proportion of cathemeral (day- and night-active) species in a community increases poleward from 18% to 68% along the same gradient. These latitudinal trends in the partitioning of diel activity time among co-occurring insect species in communities broadly reflect previously documented biogeographic patterns in the global distributions of vertebrate species occupying different temporal niches. Since diel activity patterns shape insect community dynamics, uncovering their mechanistic basis and the roles of factors such as temperature, light and biotic interactions is vital for curbing insect declines in the Anthropocene.