What governs these biodiversities?
These indices are information statistics. We are counting genetic diversity and how well it is
spread out. Remember the 1st law of ecology is that everything is in flux. Remember the rule?
Everything is in flux all the time. Eco systems are constantly being subjected to changes. Eco
systems are constantly under pressure and responding to pressure i.e. fires, earthquakes, climate
change, etc. If one species is heavily dominating the ecosystem and we have one on the margin,
if the forest fire wipes out the one individual it wipes out the species.
Example of an exam question: Name the key factor that determines biodiversity. Some are
simple. This one for instance. This is for animal populations say up in Algonquin Park. (Refer
to graph on board) You will have specifically adapted predators as well. There could be
something that has chemical compounds and one predator can’t eat it but another can. This is
where the relationship comes from. The more diverse the arsenal of species is the more complex
are the animal systems that eat the diverse. You have to look at the packages that the food comes
in and if there are many species chances are there will be many species there to eat them.
(Sea Stars) Robert Paine is a well known name. That is the keystone of well known species. It
is now a theory of keystone species governing the diversity of eco system.
Keystone species: keystone is the one thing that if you remove it what is beneath it will collapse.
In this compliment of wide degrees of species some species will be more ecologically important
than others. The keystone species, if removed, could bring the entire eco system to its knees.
That is the fear in the species protection arena of biology is that we may lose species that are
disproportionate to its abundance. If you eliminate a few individuals you could have a major
effect in the community. Robert Paine observed that a relatively simple temperate food web
contained a relatively low proportion of predatory species. He studied the Pisaster (Sea Star).
He did the experiment on Pisasters and removed them and found a drastic change happened.
You might expect that if you remove the predator (Sea Star) the prey would do better than before
but that was only true of some species and not for others.
Removing a top predator from two intertidal food webs:
What happened in both places was that before removal of the predator we had quite an
abundance of them before and afterwards the number of prey species dropped from 15 to 8 so
there was a decline. This went against expectation. He concluded the top predator was the
keystone species and if you remove it had an effect on the prey species. If you take out all the
primary producers what would happen to the ecosystem? It would collapse. This is the ‘bottom
up’ control of the ecosystem. Some say most of the time Rudy says it is top down but if you take
out the plant canopy out your eco system will fail and collapse. Ecologists love the top down
and bottom up sayings but the function of ecosystems are governed by both.
Ecosystems like the rainforests, the ‘hot spots’ of biodiversity you have by far the largest amount
of carbon fixation by plants. These are also capable of the largest values of D, ED, and H’. The
most even distribution of species occurs always in the ecosystems where we have the highest
BGYC61H3F.November.3.2008 Lecture 8 3