Pushing the Boundaries of Ecosystems

Gary A. Polis, Mary E. Power, and Gary R. Huxel, eds. Food Webs at the Landscape Level. Chicago: Univ. of Chicago Press, 2004. Pp. 548. $36.

Ask most school children to describe an ecosystem and you will likely get the response that it is a group of organisms living together in fixed a place. It is a view born of the familiar science experiment in which an experimental ecosystem is assembled by combining water, nutrients such as nitrogen, bacteria, some aquatic plants, and perhaps some herbivores such as snails or insects in a hermetically sealed glass container. The ecosystem, as such, is an economy involving a chain of production and consumption, albeit of food energy and nutrients, but an economy nonetheless. In this economy, plants produce edible tissue; herbivores eat plants and are themselves eaten by their predators; old individuals die; and the chemical constituents of their body are broken down by bacteria and recycled back through the system. This economy operates within the fixed bounds of the glass container, and if it is placed in sunlight and temperature suitable to the organisms within, it can be self-sustaining. Modern ecology, in part, capitalizes on this self-contained experimental system, although using more sophisticated apparatus and greater species complexity, to address key theoretical questions in food chain ecology (e.g., Bohannan and Lenski 2000; Kaunzinger and Morin 1998). Nonetheless, the fundamental principle that this experiment is intended to convey is that with the exception of sunlight, the food chain can support itself solely within the chemical and physical environment bounded by the glass jar.

Ecologists long ago conceptualized natural ecosystems as self-contained entities. In a now classic paper, Forbes (1887) idealizes lake ecosystems as microcosms in which the animals within them are "remakably isolated . . . so far independent of the land about them that if every terrestrial animal were suddenly annihilated . . . [it would be] long before the . . . inhabitants of the lake would feel the effects of this event in any important way." This abstraction was subsequently embraced as a convenient working way to wrestle empirically with the complexity of ecosystems. In reality, natural ecosystems, lakes included, are not altogether self-contained. In lake systems, for example, there is often seasonal runoff as melting snow in spring flows down hill slopes, carrying with it nutrients. Wind carries seeds and insects from one field into another. However, it was held that these external inputs were temporary blips, eventually dampened down by the strong food chain interactions within the systems. Thus, external inputs were viewed simply as components of the environment of the interacting organisms in the food chain. It also led to the thinking that if humans seriously disturbed natural ecosystems through inputs of their own, say phosphate pollution in lakes, those ecosystems could be restored to their original healthy state by identifying and removing those inputs (Schindler 1974).

The self-contained conceptualization of ecosystems also spawned a strong scientific tradition, continued today, in which ecologists execute finely tuned experiments with different combinations of the ecosystems' components in order to systematically build understanding of their inner workings (Resetarits and Bernardo 2002). This endeavor is likened to a clock maker fiddling with groups of interacting cogs in order to understand how all the parts piece together to make the working whole (Hochberg 1996).

As in all sciences, the way one looks at systems eventually becomes a matter of convention; and the clock maker approach to food chain ecology is no exception. Changing such perspectives requires creative mavericks who are not only unafraid to look at systems in different ways, but also argue forcefully in favor of those new ways. The late Gary Polis was one such individual. Polis essentially asked the question: what if we turn the way we look at an ecosystem on its head? That is, what if we focus...