Energy pyramid

David Eng daveng at remus.rutgers.edu
Mon Jul 18 11:47:35 EST 1994


response I received from drozd at main01.rz.uni-ulm.de
which I will post here:

In <Jul.13.13.39.20.1994.16297 at remus.rutgers.edu> daveng at remus.rutgers.edu writes:

> could someone explain to me
> the energy pyramid, where
> plants are placed on the bottom,
> above them, hebervores, then
> 1st deg. carnivores, then 2nd
> deg. carnivores, and so on?
> 
> I know it represents, in one
> respect, the % each category
> makes up in biomass, but I'm
> not quite clear on the energy
> relation (something about
> a tenfold decrease efficiency
> as you move up the pyramid?)

Hallo David,

I see that you know nearly all of the pyramid.
The reason why there is a decrease in biomass
when going up the pyramid is because every
floor consumes energy (biomass) by respiration.
Therefore you will never find the same biomass
of cows and grass within a closed system,
for example.

The value of 90 % decrease in biomass when
going up one floor in the pyramid is an 
average in some ecosystems. Generally this
value depends from the effectiveness of a
consumer of biomass in using it. So, if you
would live on an island where you could only
eat the fruits of trees, you will have a 
very small ratio of human population biomass
and tree biomass, since humans cannot use the
wood of the trees to generate biomass. On the
other side, if a population only eats salad
(whole plant), the the ratio will be greater.
However, the humans will suffer from obstipation
and the lack of vitamins and so on.

Therefore for the biomass ratios you find in 
reality there are much more factors of relevance
including competition between species.

One lesson we could learn from the energy pyramid
is that we should eat more biomass of the 
lower levels, since this level needs less energy
and, hence, less area to produce. For example,
you can harvest a greater biomass if you
get plankton animals (i.e. krill) than if you catch fish.

Ok, I hope this is what you wanted to know.

Michael

Michael Drozd drozd at rz.uni-ulm.de



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