Nighttime ecology: the ‘nocturnal problem’ revisited

The existence of a synthetic program of research on what was then termed ‘the nocturnal problem’, and which we might now call ‘nighttime ecology’, was declared more than 70 years ago. In reality this failed to materialise, arguably as a consequence of practical challenges in studying organisms at night and concentration instead on the existence of circadian rhythms, the mechanisms that give rise to them, and their consequences. This legacy is evident to this day, with consideration of the ecology of the nighttime markedly under-represented in ecological research and literature. However, several factors suggest that it would be timely to revive the vision of a comprehensive research program in nighttime ecology. These include (i) that study of the ecology of the night is being revolutionised by new and improved technologies,; (ii) suggestions that far from being a minor component of biodiversity a high proportion of animal species are active at night; (iii) that fundamental questions remain largely unanswered as to differences and connections between the ecology of the daytime and nighttime; and (iv) that the nighttime environment is coming under severe anthropogenic pressure. In this article, I seek to re-establish ‘nighttime ecology’ as a synthetic program of research, highlighting key focal topics, key questions, and providing an overview of the current state of understanding and developments.