G.E. Hutchinson’s niche concept is an abstract mapping of one aspect of population dynamics (in particular a measure of absolute fitness) onto an environmental space. For continuously growing populations, the metric is traditionally assumed to be the intrinsic growth rate, r, at low densities (with units 1/time). But at small absolute numbers, extinctions can occur for populations with a positive intrinsic rate of growth because of demographic stochasticity. Another familiar fitness metric, R0 (the expected number of offspring produced per individual over their lifetime), arises when considering extinction risk. This alternative metric can influence the shapes of niche response surfaces. This talk will broadly aim at assaying the relevance of demographic stochasticity for concepts of both absolute and relative fitness in small populations, such as at range margins and in sink habitats, with an eye towards refinement of ecological niche concepts. These different fitness metrics also have implications for how we think about species’ evolution, particularly in rapidly changing environments, and also arise in models of macroevolutionary dynamics.