The ‘Hutchinsonian niche’ as an assemblage of demographic niches: implications for species geographic ranges

Hutchinson defined the ecological niche as a hypervolume shaped by the environmental conditions under which a species can ‘exist indefinitely’. Although several authors further discussed the need to adopt a demographic perspective of the ecological niche theory, very few have investigated the environmental requirements of different components of species’ life cycles (i.e. vital rates) in order to examine their internal niche structures. It therefore remains unclear how species’ demography, niches and distributions are interrelated. Using comprehensive demographic data for two well‐studied, short‐lived plants ( Plantago coronopus , Clarkia xantiana ), we show that the arrangement of species’ demographic niches reveals key features of their environmental niches and geographic distributions. In Plantago coronopus , opposing geographic trends in some individual vital rates, through different responses to environmental gradients (demographic compensation), stabilize population growth across the range. In Clarkia xantiana , a lack of demographic compensation underlies a gradient in population growth, which could translate in a directional geographic range shift. Overall, our results highlight that occurrence and performance niches cannot be assumed to be the same, and that studying their relationship is essential for a better understanding of species’ ecological niches. Finally, we argue for the value of considering the assemblage of species’ demographic niches when studying ecological systems, and predicting the dynamics of species geographical ranges.