Identification of species’ distribution and abundance in response to environmental variability and ecosystem dynamics is the basis of much first-level work in fish ecology.  The important correlates of species distributions and abundance are informative metrics for evaluating the potential of a species to persist in a particular habitat type and what restrictions exist on the species' productivity, density, or abundance. Although these studies certainly have value, conclusions are often difficult because seemingly appropriate habitat appears under-matched by fish density. This is likely because important ecological and processes that are critical for understanding mechanisms of fish species resilience have been overlooked.  In fact, numerical density can be misleading in situations where smaller sub-populations actually have higher survivorship, fecundity or other response correlated with fitness. Behavioral and life history responses to predation risk, competition, parasites or pathogens often incorporate important selective processes that can vary significantly over a species range.  Theoretical approaches may also provide a conceptual basis to guide empirical studies that expand the understanding of mechanisms that enable species persistence in specific habitats or ecosystems.  In this symposium, we invite speakers working on a range of species responses to spatial heterogeneity in habitat conditions in aquatic, and marine environments, who have found unique insights into the ecology of the species by examining responses beyond distribution and abundance, including life history, individual condition, behavior, and plasticity in response.  We also invite speakers working on novel theoretical approaches that consider processes that affect the fitness and/or persistence of populations across the range of variation in habitat types.