Environmental Engineering Reference
In-Depth Information
Ecosystem Structure and Function Are Controlled by Many Factors
Unlike systems like the solar system, the dynamics of which are controlled by just a few
factors, ecosystem structure and function depend on many factors. Ecosystem scientists
have learned much about how ecosystems are controlled, and much of the remainder of
this topic will be concerned with this subject (see Chapter 11). Ecosystem structure and
function often are affected by organisms (including humans), either through trophic activi-
ties such as herbivory, predation, and decomposition, or through engineering activities
( Jones et al. 1994 ) such as burrowing, shelter construction (beaver dams), and the like
(see Box 11.1 in Chapter 11). Likewise, the nonliving parts of ecosystems often control eco-
systems by determining supplies and movement of air, water, key nutrients, and other
materials. Temperature is another abiotic factor that has strong effects on ecosystems.
Finally, because most ecosystems are open and exchange energy and materials with the
ecosystems that surround them or that preceded them, the structure and function of an
ecosystem can be strongly affected by its spatial and temporal context (see Chapter 10).
Ecosystems Change Through Time
Ecosystems change through time (see Chapters 10 and 11). These changes may be grad-
ual and subtle (the millennial losses of minerals from a weathering soil) or fast and
dramatic (a fire sweeping through a forest). Both external forces (changes in climate or
nutrient inputs) and internal dynamics (aging of a tree population, accumulation or deple-
tion of materials in a soil or a lake) are important in driving temporal changes in ecosys-
tems. In some cases, changes are directional and predictable (e.g., soil weathering, the
filling of a lake basin), while in other cases changes may be idiosyncratic and difficult to
predict (e.g., the arrival of an invasive species, disturbance by a hurricane). Understanding
and predicting how ecosystems change through time is of great theoretical and practical
interest, and is a major part of contemporary ecosystem science.
How Do We Classify or Compare Ecosystems?
Thus, ecosystem scientists use structure, function, control, and temporal dynamics to
classify and compare ecosystems. For instance, it is common to see ecosystems described
as rich in nitrogen (structure), sinks for carbon (function), fire-dominated (control), or
recently disturbed (dynamics). All of these attributes of ecosystems can provide useful
frameworks to classify ecosystems, and ultimately to organize and interpret the vast
amount of information that scientists have collected about ecosystems. Similar descriptions
and classifications are evident throughout the topic.
WHY DO SCIENTISTS STUDY ECOSYSTEMS?
Scientists have been motivated to study ecosystems for several reasons. To begin with,
if ecosystems truly are the “basic units of nature” on Earth, any attempt to understand our
planet and the products of evolution on it must include ecosystem science as a central
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