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Virtual
Ecosystems -- System Concepts
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A system is a group of interacting parts that function
as a whole. A system is distinguishable from its
surroundings by recognizable boundaries. The system
exhibits more than the collective properties of the
parts themselves. Additional behavior attributed only to
the system is a result of interactions between the
parts. This additional behavior is often referred to as emergent
behavior .
A gasoline engine is an example of emergent behavior
where locomotion is provided only because the pistons,
crankshaft, carburetor, and other parts are interacting
with each other under a given set of rules. The
configuration of a system's parts can be physical,
logical or statistical. A system can show unexpected
features that cannot be reduced to a property of the
individual parts. The system's behavior depends upon the
nature and arrangement of the parts and usually changes
if parts are added, removed or rearranged.
The system has emergent behavior if the behavior is not
found within any of the parts and exists only at a
higher level of description. To understand a system, it
is necessary to study not only parts and processes in
isolation, but to study the systematic organization and
the relationships between the unifying the parts. The
study of the system's organization is crucial because
the behavior of the parts is different in isolation than
when acting as an integrated whole.
Another important development has been a change in the
view of how energy flows to and from a living system.
The second law of thermodynamics states that the general
trend of events in physical nature is toward states of
maximum disorder and the leveling out of differences,
with the so-called heat death of the universe as the
final outcome. All energy is degraded into evenly
distributed heat of low temperature and the world
process comes to a stop. The measure of disorder is
called entropy. The tendency towards maximum entropy is
the tendency to maximum disorder.
The problem is that the second law applies only to
closed thermodynamic systems such as engines. Every
living organism is an open system that moves towards
higher order, heterogeneity, and organization. It
maintains itself with a continuous inflow and outflow of
energy. It builds up and breaks down chemical
components, never being, so long as it is alive, in a
state of chemical and thermodynamic equilibrium.
Instead, it maintains energy flow in a steady state
until death.
Living systems that maintain themselves in a steady
state can avoid the increase in disorder and can develop
towards states of increased order and organization. This
chemical process within living cells is called
metabolism. It is the very essence of that fundamental
phenomenon of life. And, because ecosystems are
collections of living elements, they are also open
systems.
Information flow into a system is similar the increase
of order. Therefore the degree of information flow is a
measure of order or degree of organization. The concept
that more information brings more order is generally
intuitive.
In any closed system, the final state is defined by the
initial conditions. The motion of a planet at a given
time is determined by a position at some previous time.
In a chemical equilibrium, the final concentrations of
the reactants depend on the initial concentrations. If
either the initial conditions or the process is altered,
the final state will also be changed to a predictable
value. In open systems the same final state may be
reached from different initial conditions and in
different ways. This is is called equifinality, and it
has a significant meaning for the phenomena of
biological regulation.
People who study systems call the final equilibrium
state reached by a system an "attractor"
because it appears to attract different pathways to it.
For example, a perfectly normal sea urchin (the
attractor) can develop from (1) a complete ovum, (2)
from each half of a divided ovum, or (3) from the fusion
product of two whole ova. The same applies to embryos of
many other species, including man, where identical twins
are the product of the splitting of one ovum. Attractors
are discussed later.
In certain systems, a final state may be totally
dependent on initial conditions. In fact, any miniscule
change in an initial condition can cause a complete
change in the final steady state. This special class of
system is called a chaotic system.
Another central systems concept is the idea of feedback
where the output of a system is used to control or
regulate the input. First, a system has a receptor or
"sense organ," be it a photoelectric cell, a
radar screen, a thermometer, or a sense organ in an
organism. The message to the receptor may be, in a
living organism, represented by nerve conduction such as
an eye. The system also contains a center that processes
the incoming messages and transmits them to effecters
that may consist of a muscle that responds to the
incoming message in such a way that there is an output
of energy. Finally, the functioning of the effecter is
monitored by the receptor. This makes the system
self-regulating and guarantees stabilization or
direction of action.
There are many biological phenomena that correspond to
the feedback model. One such phenomenon is
thermoregulation in warm-blooded animals. Cooling of the
blood stimulates certain centers in the brain which
"turn on" heat-producing mechanisms of the
body, and the body temperature is monitored back to the
center so that temperature is maintained at a constant
level.
In fish schooling, the pressure sensitive lateral line
of a fish senses the proximity of its nearest neighbors.
The fish's feedback mechanism performs any necessary
corrections in navigation. Fish schooling is an example
of emergent behavior where the real feedback mechanism
is contained in the individual fish even though it
appears that the ecosystem (the fish school) has a
feedback mechanism. Emergent
behavior is discussed further.
The above description of feedback is generally called
"negative feedback" because it describes a
conteracting response. However, ecosystems also
experience "positive feedback" where a change
or growth in the system is promoted in the same
direction as the initial change action. The act of two
or more fish getting together to create a school is an
example of positive feedback. As other fish of the same
species encounter the school, they join the school
resulting in a larger school.
Systems can also demonstrate a characteristic called
self-organization. This widely studied phenomenon causes
a system to appear as if it has organized itself. In
fact, self-organization is an emergent behavior caused
by the actions of all individuals within the system.
Fish schooling is an example of self-organization. Self-organization
of ecosystems is discussed further.
An exciting result of the study of order in systems is
the appearance of similar behaviors, or isomorphisms, in
systems that were always thought to be widely different.
For example, an exponential law of growth applies to
certain bacterial cells, to populations of bacteria, of
animals or humans, and to the progress of scientific
research measured by the number of publications in
genetics or science in general. The entities in
question, such as bacteria, animals, men, books, etc.,
are completely different, and so are the causal
mechanisms involved. Nevertheless, the mathematical law
is the same. Or, there are systems of equations
describing the competition of animal and plant species
in nature. But it appears that the same systems of
equations apply in certain fields in physical chemistry
and in economics as well. |
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