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Ecology is a science of defined boundaries.
Whether looking at a population
(collection of all individuals), a community
(collection of “all” species), or an ecosystem
(collection of “all” factors, biological, chemical, and
physical), just the definitions make it clear that
boundaries need to be set.
When looking into an ecosystem, how much
territory is included – where are the physical
boundaries? How
many factors are looked at – as many as you can measure,
or just the ones that you believe are relevant to your
study? The same
considerations apply to which species get included in
the studied community.
Since it isn’t possible to include, or even to
know, them all, much will be excluded and parameters
must be set. In
many cases, there will be a loosely-established,
accepted definition of the various levels.
Physical / chemical factors
will include such things as temperature, available water
and nutrients, and usable energy.
Ecosystems have tolerance limits – ranges
of these factors within which the ecosystem can persist;
there are of course optimum levels for each
factor, which may or may not be known.
As systems interact with the global rise in
greenhouse gases, it has become critical to try to
determine how much those effects will perturb their
biological aspects.
Niches
are “roles” played by species with an ecosystem. There
are often broadly described roles, such as ground-cover
plants, canopy-producing plants, browsers, climbers,
etc. Not every
niche is available in every ecosystem – niches may have
tolerance limits as well. Some ecosystems, especially
physically isolated ones, may have available niches with
no occupying species. Ecospecies
is a term applied to different species filling the same
niche (again, with defined parameters) in different
ecosystems. Some
niches are defined as relationships, such as
predator and prey, parasite and host.
Symbiosis implies
a strong reliance between two species, which may benefit
both, mutualism, or just one, commensalism.
Food webs
are an attempt to track the flow, usually of energy,
through an ecosystem.
At the base of the web is primary production
from the synthesizers, usually those that convert
frequencies of light to chemical bond energy, through
photosynthesis, but in some rare ecosystems such as
ocean-floor hydrothermal vents, where
chemosynthesis essentially uses heat to help form
chemical bonds.
Of course, the available energy is not all converted –
in fact, the efficiency of the production level is
pretty low. In an
ecosystem, net primary production, where the
energy usage of the producers themselves is
factored out as not part of the web, is a common
calculation. This
first level is the trickiest – for a long time, the need
for producers in every known food web stymied the
production of theories about the beginnings of Life.
This was known as the plant problem, since
only photosynthetic producers were known.
The discovery of primordial soup (“food”
established from organic space dust components) and
chemosynthesis helped toward working out the first
steps.
Consumers depend upon the base – from there up,
energy shifts from chemical bond to chemical bond.
At every conversion, however, some if the energy
is lost as random particle motion – heat,
basically, according with the Second Law of
Thermodynamics, also known as the Law of Entropy.
This means that less and less energy is
available with every step “up” in the levels. The
“leftover” chemical bonds in dead things and
incompletely-processed wastes are used by the
decomposers, providing the raw materials for the
producers to rebuild with.
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