November 3 2008
Focus on things that are quantitatively definable ( , , and ) is testable material. What are the
3 types of biodiversity are there? You could answer in 2 ways either by definition or by , , or
diversity. How do you know? Read the questions. The multi-part questions are very likely to
be on the exam. I may ask you to calculate for me diversity and quantify certain diversity. You
can only do that if you define them correctly. The next part could be a definition of the 3
diversities and on what level are they operating. Can you give me 2 indices that quantitatively
define diversity? Can you give me a definition of diversity? What is it?
S: You could use the Sorenson index and it is used at the scale.
P: The scale will be in the answer and then you have to somehow define the terms with
reasonable scientific definition.
Calculating species diversity (H’) for two hypothetical communities of forest trees.
The Shannon-Wiener index is probably the most often used. We also have the Simpson’s
Index. On this chart we have 5 tree species. (Reads graph) You already know that both indices
above attempts to accomplish the total number of species and also less easily done is to appraise
how many of the species are in what area. In this case 84% of the trees samples were species 1
and the rest were species 2, 3, 4, and 5. You use a percentage and add them up to 100%.
What is less obvious is what happens less for the Shannon-Wiener Index. Take your calculator
to your exam in case you have to calculate something. Logepi are to the base of e the natural
logarithm. In biodiversity it is usually e which you are familiar with as lne which has a numerical
value of 2.7 roughly (you should know that). Take that natural logarithm and you get the Pi
values. Notice how the log of the largest number becomes numerically the smallest number with
a – in front of it. The Shannon-Wiener Index is figures out for each line item. You sum them
up, get the value (notice it is positive) and the negative is there because the sum can’t be a
What does the value mean? It means something when you go comparative i.e. community A and
B in this case. Then you do the last column and sum it up. The larger it is the more diverse
the community is considered to be by ecologists.
The Shannon-Wiener Index can figure out the maximal biodiversity for an eco system for a
given number of species (no matter what the number). The Shannon-Wiener index in the most
diverse system here are all distributed with perfect evenness of distribution is the natural
logarithm of the species. Take the natural logarithm of 600 = 6.39 if the 600 species are
distributed with perfect evenness and this means each of the species occupies 1/600th of the
BGYC61H3F.November.3.2008 Lecture 8 1
space. With the Shannon-Wiener Index if you get 6.39 it is about as high as you can get. If you
get 6 in the tree community you are in the top ecosystem in the world. The ‘hot spots’ identified
S: Is it possible to get higher than 6.3 if you take insects?
P: Of course the Shannon-Wiener Index depends on the type of species you are looking at. E.
O. Wilson is an insect specialist that will err on the side of the higher numbers. Likewise he
would say if there are 600 species of tree then each tree up in the canopy could have 1,000
species of insects in it etc. That is based on small surveys in rainforests in S. E. Asia. There will
be some insects will occur in one species and not in another. When you hear things by Wilson
divide by either 2 or 10 because he exaggerates.
The Simpson’s Index is similar but there is no logarithm involved. They look at percent
coverage of the sample. Take Pi values and square them for each entry and then sum them. You
then take the reciprocal. Take the simple community of .2 so what is that squared? Pi = 0.2 =
0.04 and then sum them all up so we have 5 of these = .2 just like the Shannon-Wiener Index. .
84 squared is what? We go back to .2 and sum Pi squared values and take the reciprocal of the
value which is 5. The Simpson’s Index for this community is 5. This value is called the D value
and the D is for diversity. This is nice because this index tells you if you have 5 evenly
distributed then the D value is 5. That is the maximum number. The second community is 1.35
so now you take 1/1.35 (like I told you to do at home) and you get 0.74 which is a lot smaller.
Ecologists like to calculate the ED = D/S which is the equitability value. How equitably/evenly
are the species distributed? What does this do? This takes the D value and multiples it by the
number of species. D = 5, ED = 5/5 = 1. The ED number goes from 0 to 1 and the closer to 1
means the eco system is equitable. ED = 0.149. 64 is the number of tree species in this part of
Canada that are native. You can plant other trees that are not native of course and you will learn
about this by urban gardening in the presentation later. As far as native species 64 is our
maximum here. If you looked at bird species it is about 200 depending on the species you are
looking at. You can take those numbers and figure out the Shannon-Wiener Index.
You should never forget these two pinnacles of biodiversity.
Rank-abundance curves for two hypothetical forests:
(Reads graph) In a plot like this that we call the ‘rank-abundance curve’ for a community you
can appraise graphically the distribution in terms of evenness and the overall number of species.
You have 5 species you can’t go higher up than 5. Rank-abundance is plotted as semi-
logarithms log to the base of 10. Logarithms are essential to understand nature and medicine so
read up on them.
The higher the slope of a rank-abundance curve if there is one the less diverse that community
will be on account of its equitability of distribution. These are good first appraisals and very
good if the number of species is similar to one another otherwise you use the Simpson’s Index or
the Shannon-Wiener Index.
BGYC61H3F.November.3.2008 Lecture 8 2
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
Focus on things that are quantitatively definable ( , You could answer in 2 ways either by definition or by. The multi-part questions are very likely to be on the exam. I may ask you to calculate for me diversity and quantify certain diversity. You can only do that if you define them correctly. The next part could be a definition of the 3 diversities and on what level are they operating. S: you could use the sorenson index and it is used at the. P: the scale will be in the answer and then you have to somehow define the terms with reasonable scientific definition. scale. Calculating species diversity (h") for two hypothetical communities of forest trees. The shannon-wiener index is probably the most often used. In this case 84% of the trees samples were species 1 and the rest were species 2, 3, 4, and 5. You use a percentage and add them up to 100%.