Since The Beginnings Of Ecology

Ecosystems have directionality! This is an extraordinary statement, although the reader might at first wonder why. After all, one observes directional behavior everywhere: A billiard ball, when struck by another ball, will take off in a prescribed direction. Sunflowers turn their heads to face the sun. Copepods migrate up and down in the water column on a daily basis. Yet, despite these obvious examples, scientists have increasingly been trained to regard instances of directionality in nature as having no real basis—epiphenomenal illusions that distract one from an underlying static, isotropic reality.

Before embarking on how ecological direction differs from directionality observed elsewhere, it is worthwhile describing the ecological notion of succession (Odum, 1959). The classical example in American ecology pertains to successive vegetational communities (Cowles, 1899) and their associated heterotrophs (Shelford, 1913)— research conducted on the shores of Lake Michigan. Both Cowles and Shelford had built on the work of the Danish botanist, Eugenius Warming (1909). Prevailing winds blowing against a shore will deposit sand in wave-like fashion. The most recent dunes have emerged closest to the lake itself, while progressively older and higher dunes occur as one proceeds inland. The assumption here, much like the famed ergodic assumption in thermodynamics, is that this spatial series of biotic communities represents as well the temporal evolution of a single ecosystem. The younger, presumably less-mature community consisted of beach grasses and Cottonwood. This "sere" was followed by a Jack pine forest, a xeric Black oak forest, an Oak and hickory moist forest, and the entire progression was thought to "climax" as a Beech-maple forest. The invertebrate and vertebrate communities were observed to segregate more or less among the vegetational

Line Chart

Line Chart

60 65 70 75 80 85 90 95 100 year

Figure 4.1 Increase over time in the number of plant species found on the newly created island of Surtsey.

60 65 70 75 80 85 90 95 100 year

Figure 4.1 Increase over time in the number of plant species found on the newly created island of Surtsey.

zones, although there was more overlap among the mobile heterotrophs than among the sessile vegetation.

Other examples of succession involve new islands that emerge from the sea, usually as the result of volcanic activity. One particular ecosystem that was followed in detail is the sudden emergence in 1963 of the approximately 2.8 km2 island, Surtsey, some 33 km south of the large island of Iceland in the North Atlantic. Figure 4.1 depicts the rise in the number of plant species found on the island. (Other measures of succession on Surtsey will be given below).

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