The Effect of Pattern on Process1

Ecology and natural history have a long tradition of interest in the spatial patterning and geographic distribution of organisms. The latitudinal and altitudinal distribution of vegetative zones was described by Von Humboldt (154), whose work provided a major impetus to studies of the geographic distribution of plants and animals (74). Throughout the nineteenth century, botanists and zoologists described the spatial distributions of various taxa, particularly as they related to macroclimatic factors such as temperature and precipitation (e.g. 21, 82, 83, 156). The emerging view was that strong interdependencies among climate, biota, and soil lead to long-term stability of the landscape in the absence of climatic changes (95). The early biogeographical studies also influenced Clements’ theory of successional dynamics, in which a stable endpoint, the climax vegetation, was determined by macroclimate over a broad region (14, 15). Clements stressed temporal dynamics but did not emphasize spatial patterning. Gleason (36-38) argued that spatially heterogeneous patterns were important and should be interpreted as individualistic responses to spatial gradients in the environment. The development of gradient analysis (e.g. 17, 164) allowed description of the continuous distribution of species along environmental gradients. Abrupt discontinuities in vegetation patterns were believed to be associated with abrupt discontinuities in the physical environmerit (165), and the spatial patterns of climax vegetation were thought reflect localized intersections of species responding to complex environmental gradients.