Environmental Engineering Reference
In-Depth Information
CHAPTER
9
Revisiting the Ecosystem Concept:
Important Features That Promote
Gener
ality and Underst
anding
Michael L. Pace
Department of Environmental Sciences, University of Virginia, Charlottesville
INTRODUCTION
Having learned about fundamental topics such as production, energy flow, and elemen-
tal cycling, we now reconsider some of the important features of the ecosystem concept.
Recall that the study of an ecosystem requires defining boundaries. Thus, ecosystems are
places defined by investigators. Ecosystems can be as small as a culture flask in a labora-
tory or as large as the entire Earth. The size of an ecosystem is flexible (“one size does not
fit all”) and depends on the questions being asked and the feasibility of measuring flows
across ecosystem boundaries. By placing boundaries on an ecosystem, a mass balance
approach can be applied tracing inputs, outputs, and storage over time. Mass balance pro-
vides a constraint that structures many ecosystem studies and gives the approach power
to resolve questions and problems through an accounting of fluxes. Because ecosystems
include both biotic and abiotic components, ecosystem studies are inherently inclusive.
This inclusive approach means that the ultimate goal of ecosystem research is not to
reduce or isolate specific components but rather to understand the system that results
from the interactions of the components as a whole. Boundary specification, mass balance,
and inclusiveness are three of the most important features of the ecosystem concept, and
provide flexibility, power, and synthesis.
Despite the apparent strengths of the ecosystem concept, we could object to the
approach on a number of grounds. Does the flexibility of ecosystem specification make the
analysis of ecosystems too dependent on investigator-defined units and thereby prevent
generality? For example, a study of carbon cycling might be done in a flask or for the
