Environmental Engineering Reference
In-Depth Information
SECTIONII
ECOLOGICAL ENERGETICS
INTRODUCTION
All organisms need materials such as carbon, nitrogen, and phosphorus to build
molecules, cells, and other structures, and energy to build and maintain those structures
against the relentless forces of entropy. Not surprisingly, the two main branches of ecosys-
tem science deal with the movement and fate of materials and energy (biogeochemistry and
ecosystem energetics, respectively). This section of the topic (Chapters 2
4) introduces eco-
system energetics (primary production, secondary production and consumer energetics,
and decomposition), and Section III deals with biogeochemistry (Chapters 5
8).
Studies of energy flow through individuals, populations, communities, and ecosystems
form a large part of past and present-day ecosystem science. Historically, ecosystem scien-
tists studied energy flow for several reasons. Many of the earliest studies (i.e., before 1950)
were motivated by the idea that the allowable harvest from a wild population (e.g., a fish-
ery) would be related to the amount of energy flowing into that population, so that studies
of energy flow would help to estimate sustainable yield. Although historically important,
this is no longer a primary motivation for ecological energetics (but see
Libralato et al.
2008
for a modern example). More generally, ecologists recognize that energy is essential
for all life; thus, studies of energy flow track the movement of a key resource. Because
all organisms require energy, it provides a common currency that allows ecologists to
make comparisons across all organisms and habitats. That is, it allows ecologists to compare
the activities of such disparate organisms as plants, mice, moose, and microbes using the
same single currency that is required by all of them.
Some ecologists have gone further to regard energy as the key resource, making the
case that energy can be substitutable with other resources (e.g., water, nutrients) so that
deficiencies in any resource can be ameliorated if enough energy is available. In this world
view, which was held by a minority of ecologists, energy is the ultimate limiting resource,
so pathways of energy flow might reveal pathways of control in ecosystems. Finally,
energy flow often is roughly proportional to other key activities (e.g., grazing, flows of
elements), so it could be argued that energy flow is the most appropriate single measure
of the importance of a population (if we must reduce a population to a single number),
because it roughly summarizes the multiple activities that the population performs.
