What is the
difference between ecosystems and other systems? The main difference is that in
ecosystems feedbacks are present.
Ecology deals with a disparate array of things: flow of matter and energy,
bioclimate, niches, population biology, competition, evolution, food webs,
macroecology, but I am convinced that the unifying concept is that of feedback.
Other systems can be very complex, but they present no loops. An exception is
perhaps economy, where a few feedbacks are present.
It is often
not realised that when you have a causal loop, like in the figure, you can do
no statistics and even any quantification is difficult
In fact you
cannot have differet fixed levels of A in order to study the relationship AB;
when you increase A f a quantity g, it will increase a larger (or a lesser)
quantity g + h due to indirect relationship via
C.
But there
is a way to turn around this problem. If you have a causal branch in the
network that ends in D, measuring D you can asses the state of the loop ABC. The element D is an indicator. Ecologysts often frown at indicators they are
reductionist, and they believe that elements indirectly related to a system are
unimportant. And yet indicator are the only way to quantify
the elements of the system when loops – i.e. feedbacks – are present. The usual
method is to build a reasonable model and to compare the prediction with the
patterns observed. The problem is that the number of models that are compatible
with observation is usually immense. Moreover, history of science teach us that
often scientific laws are not reasonable
– it is neither intuitive nor reasonable
that the sub turns around the earth, it seems exactly the opposite.
But I am
afraid that it will take much untile ecologists will recognize that they look
at ecosystems the worng way. Think for a moment to the successful theories in
ecology, like island biogeography, they always concern systems without loops.
The problems begin when you have loops.
Nessun commento:
Posta un commento