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Animals are facing novel 'timescapes' in which the stimuli entraining their daily activity patterns no longer match historical conditions due to anthropogenic disturbance. However, the ecological effects (e.g., altered physiology, species interactions) of novel activity timing are virtually unknown. We reviewed 1328 studies and found relatively few focusing on anthropogenic effects on activity timing. We suggest three hypotheses to stimulate future research: (i) activity-timing mismatches determine ecological effects, (ii) duration and timing of timescape modification influence effects, and (iii) consequences of altered activity timing vary biogeographically due to broad-scale variation in factors compressing timescapes. The continued growth of sampling technologies promises to facilitate the study of the consequences of altered activity timing, with emerging applications for biodiversity conservation. Recent years have seen a growing interest in the role of time in structuring biological patterns and processes. Among nature's most dramatic and universal temporal patterns are the daily activity patterns shown by organisms. Although the endogenous mechanisms (e.g., circadian rhythms) giving rise to such patterns have been researched extensively, ecological aspects of daily activity patterns are now receiving greater attention. Plasticity in daily activity patterns may represent an in situ adaptation to human-mediated stressors such as climate change and urbanization. However, the effects of novel activity timing, which may emerge at multiple levels of biological organization, are poorly understood. We offer hypotheses to catalyze future research on the ecological consequences of altered daily activity timing and discuss approaches that may facilitate such investigations. [ABSTRACT FROM AUTHOR]