Three kinds of biological hierarchies that form the basis of biological integration and scaling. A) Physiological: Hierarchy of functional or metabolic units within a plant from genes, metabolites (small molecules) to organelles, cells, leaves to the whole plant. B) Evolutionary: Hierarchical organization of the tree of life from individuals to lineages. C) Ecological: Nested spatial scales showing that ecological and biogeographic processes—from density- and frequency-dependent neighborhood interactions to environmental sorting, dispersal and biogeographic processes—that drive the distribution and diversity of life and shift with increasing spatial and temporal scales.