Environmental Engineering Reference
In-Depth Information
measure the function (input and output) of a box (the ecosystem) without having to know
what is in the box (
Figure 1.3
). Sometimes ecologists debate whether it is philosophically
possible to predict the properties of a complex system by studying its parts (reductionism)
or whether it is necessary to study intact systems (holism). It is not necessary to accept the
philosophical claims of holism, though, to recognize that studies of whole systems may be
a much more efficient way than reductionism to understand ecosystems. Such a holistic
approach to ecosystems is a powerful tool of ecosystem science, and is often combined
with reductionist approaches to develop insights into the functioning and controls of
ecosystems.
Third, the definition gives the investigator complete flexibility in choosing where to set
the boundaries of the ecosystem in time and space. The size, location, and timescale at
which ecosystems are defined can therefore precisely match the question that the scientist
is trying to answer. Boundaries often are drawn at places where fluxes are easy to measure
(e.g., a single point on a stream as it leaves a forested-watershed ecosystem) or so that
fluxes across the boundary are small compared to cycling inside the ecosystem (e.g., a lake
shore). Nevertheless, boundaries are required to make quantitative measures of these
fluxes. It is true that ecosystems frequently are defined to be large (e.g., lakes and water-
sheds hectares to square kilometers in size) and are studied on the scale of days to a few
years, but there is nothing in the definition of ecosystem that requires ecosystems to be
defined at this scale. Indeed, as you will see, an ecosystem may be as small as a single
rock or as large as the entire Earth, and can be studied for time periods as long as hun-
dreds of millions of years.
Fourth, defining an ecosystem to contain both living and nonliving objects recognizes
the importance of both living and nonliving parts of ecosystems in controlling the func-
tions and responses of these systems. There are examples throughout the topic in which
living organisms, nonliving objects, or both acting together determine what ecosystems
look like (structure) and how they work (function). Furthermore, the close ties and strong
interactions between the living and nonliving parts of ecosystems are so varied and so
strong that it would be very inconvenient to study one without the other. Thus, the
ECOSYSTEM BOUNDARY
ORGANIC COMPARTMENT
ATMOSPHERIC
COMPARTMENT
Litter
Biological uptake
Meteorologic
Geologic
Biologic
Meteorologic
Geologic
Biologic
of gases and aerosols
Herbicore
Carnivore
Windblown particulates
and gases above and
below ground
Living
Dead
Biomass
Biological release of
Plant
Biomass
Omnivore
Detritivore
gases and organic aerosols
BIOSPHERE
BIOSPHERE
T
T
AVAILABLE NUTRIENT
COMPARTMENT
SOIL AND ROCK
MINERAL
COMPARTMENT
Weathering
Meteorologic
Geologic
Biologic
Meteorologic
Geologic
Biologic
on
in
soil
solution
Formation of
exchange
sites
secondary minerals
INTRASYSTEM CYCLE
FIGURE 1.3
Two views of the same ecosystem. The left side shows some of the parts inside an ecosystem and
how they are connected, as well as the exchanges between the ecosystem and its surroundings, whereas the right
side shows a black-box approach in which the functions of an ecosystem (i.e., its inputs and outputs) can be stud-
ied without knowing what is inside the box. (Modified from
Likens 1992
.)
