Spatial Heterogeneity: Structure Over Space
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).
KeywordsSpatial Heterogeneity Internal Wave Gulf Stream Neighbor Distance Nest Male
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- Distributions of nearest neighbor distances are usually calculated by compiling distances on a plane from only one of the four possible 90° quadrants; this makes it possible to include distances between individuals situated in different aggregations. Otherwise, nearest neighbors would always be within aggregation and the distribution of nearest neighbor distances would not include any reflection of the distribution of patches, an important aspect of spatial structure.Google Scholar
- We saw earlier that mysid distributions tended toward aggregation at higher densities (Fig. 13–6). The process of sampling collects swarms or parts of swarms so that the individuals appear aggregated. This is a matter of size of the sample unit, as discussed in reference to Figure 13–4.Google Scholar
- These samples were collected with a modified Longhurst—Hardy plankton recorder (LHPR). This device enables the collection of a series of samples as it is towed through the water. Ribbons of mesh are rolled across the cod end of the net so that the plankton from different sections of the tow are caught on successive portions of the mesh. New versions of the LHPR reduce difficulties of net avoidance by fast-swimming copepods, extrusion of specimens through the mesh and the hang up of specimens along the net (Haury et al., 1976). A number of other instruments were used to measure temperature, salinity, and chlorophyll (Haury et al. , 1979) .Google Scholar