Spatial Structure: Patchiness
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 105–108 m within any linear transect in Fig. 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. 13.1a, b). Measurements of numbers of zooplankton m−2 off the California coast show patches of tens of meters (Fig. 13.2); 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). Plankton recorders (for example, Davis et al. 1992) provide data over spatial scales of microns to hundreds of meters, confirming the presence of aggregated distributions of organisms at scales of 20 cm–200 m.