Ecosystem-size relationships of river populations and communities

The fractal-like branching of river networks and connectivity with riparian areas and groundwater mean that rivers have longitudinal, lateral, vertical, and temporal dimensions.We argue that the development of scaling relationships between ecological properties and river size and investigation of fragmentation effects can improve understanding of this multidimensionality.Stream metabolic processes scale with river size, driven mainly by downstream accumulation of resources and changes in boundary interface dimensions.Aspects of predator size, population size, richness, community stability, and food-web structure vary with river size, but scaling relationships are most likely when physical constraints limit body size or movements or when space limits affect community assembly.Assessment of the occurrence, shape, and universality of ecosystem-size relationships, especially their scaling, will inform river management. Knowledge of ecosystem-size influences on river populations and communities is integral to the balancing of human and environmental needs for water. The multiple dimensions of dendritic river networks complicate understanding of ecosystem-size influences, but could be resolved by the development of scaling relationships. We highlight the importance of physical constraints limiting predator body sizes, movements, and population sizes in small rivers, and where river contraction limits space or creates stressful conditions affecting community stability and food webs. Investigations of the scaling and contingency of these processes will be insightful because of the underlying generality and scale independence of such relationships. Doing so will also pinpoint damaging water-management practices and identify which aspects of river size can be most usefully manipulated in river restoration. Knowledge of ecosystem-size influences on river populations and communities is integral to the balancing of human and environmental needs for water. The multiple dimensions of dendritic river networks complicate understanding of ecosystem-size influences, but could be resolved by the development of scaling relationships. We highlight the importance of physical constraints limiting predator body sizes, movements, and population sizes in small rivers, and where river contraction limits space or creates stressful conditions affecting community stability and food webs. Investigations of the scaling and contingency of these processes will be insightful because of the u