OVERVIEW

Part of our admiration for nature stems from the fact that it continually surprises us with its infinite variation, regardless of the scale of observation. This holds true of microscopic worlds; the surface of a cell for example, consists of myriad buoyant macromolecules distributed haphazardly in a viscous lipid sea. On the broad scale, that of continents or ecosystems, the fabric of habitats is like a patchwork quilt with a wide variety of local conditions, some favoring one species, some favoring another.

For this reason, real natural systems behave in a way that reflects an underlying spatial variation. Despite our idealizations, no species actually consists of identical individuals, since not all individuals are equally exposed to a constant environment. Similarly, on the molecular level, rarely do reactions take place in a homogeneous soup of chemicals. Somehow the effect of spatial organization does influence the way individual particles or molecules interact.

In the three chapters to follow, our purpose is to expose how spatial variation influences the motion, distribution, and persistence of species. We shall see that in the fine balance...