Spatial Heterogeneity: Structure Over Space

Abstract

In general, organisms are not distributed uniformly over space; consider for example, the distribution of primary production over the world’s oceans (Fig. 2–30). Moreover, such heterogeneity occurs at all spatial scales. We can use the size of a patch of higher abundance or the distances among such patches as a way to assess the scale of heterogeneity. There are significantly higher or lower rates of production in distances of 10⁵ to 10⁸ m within any linear transect in Figure 2–30. Spatial variability is also pervasive at smaller distances: the variation in concentration of dissolved CO₂ in surface waters of the Gulf of Maine is evidence of spatially heterogeneous biological activity on a scale of 10⁴-10⁵ m, while the variability in concentration of chlorophyll in St. Margaret’s Bay, Nova Scotia, varies on a scale of about 10⁴ m (Figs. 13–1 a,b) . Measurements of numbers of zooplankton m^-2 off the California coast show patches of tens of meters (Fig. 13–2c); a careful examination of spatial variability of phytoplankton production shows significant patches in a scale of 10^-1 m, most clearly in samples from the Gulf Stream (Fig. 13–1d).