BIOB50 ECOLOGY LECUTRE NOTE
SLIDE BY SLIDE
SLIDE 17
3 different schools of thought that what contributes to
diversity.
1.
These resources are portioned between species.
2.
Because of these disturbances and fluctuating
conditions one dominant spcies is unable to reach its carrying capacity and
exlclude other species.
3.
The species traits don’t matter any more. So the
identity of the species is irrelevant.
SLIDE 18
Competitive exclusion model – this is something we always
don’t observe in the natural world. A good example of this is the Paradox of
plankton.
SLIDE 19
The species partition resources in order to reduce
competition with one another. Using the resources in different ways.
SLIDE 20
If we have here on the x acis the different types of resources
available to a species, and each of these curves represents the species. The y
axis represents the varaiblity of the resource availbe, how many different
types of trees, not teumber of trees availab.e
SLIDE 21
This overlap rerpresents then, the purple, the degree of
competition these 2 different speices show for a resources. So when there is
more overlap, they compete more for resources, and in extreme case where they
completely overlap is the outcome of competition of exclusion principle, where
only one species can exist, and driving the other to extinction.
SLIDE 23
Where you see less overlap, there is more partiionign of the
resources, therefore less competition among the species.
SLIDE 24
Resource partitioning can lead to a higher species richness.
First there may be some kind of specialization. All these
species have very little overlap.
SLIDE 25
Species richness in a community can also be high because the
resource spectrum is broad, in other words there are a great array of resources
available and so it can support more species.
SLIDE 26
McArhtur wanted to know how these birds were co existing
with other even though they had similar resource needs.
SLIDE 27
The finding showed that mcarthurs hypothesis that they were
using the same hbitat, and resurces
SLIDE 28
McArthur examined bird diversity and....foliage denity
SLIDE 29
He found yes there is actually a psotive relationship etween
species diversity and members of thje..
Interesting he also found group identity was not realed to the. S
SLIDE 30
Species can co exist by using the resources in different
proportions.
SLIDE 31
The test says that within an experimental setting
SLIDE 27
What important is that hes speciues were only to able to
coexist with another bothj phosphorous and
silicon need each other.
SLIDE 22
What is allowing for coextence then is this idea there are
these seasonal turn overs in the lake. These disturbances are frequent enough
to keep certain species in check so tjheyu don’t reach their carrying capacity.
SLIDE 33
He proposed the co
existence Can be maintained even when a disturbance occurs. What he did was he
manipulated the population of the starfish for coastal waters. He had a control
and a aniupatled. In control the predatory starfish was left alone and was
allowed....in the manipulated he removed the predatory starfish, and so what he
found was for pods without the predatory starfish, the secies richeness was
actually pretty low. Withoutht eh predatory starfish, themuscle outcompeted
other barnacles. In the control, species richness was actually higher, the
starfish was keeping the muscles in check and reaching its carrying capacity.
So wht we’d ecpect tp find in high disturbance areas are
good colonizers becaue they are the species that can establish quickly after a
disturbance.
SLIDE 35
The immedietate disturbance hypothesis – so this theory, low
levels of disturbance, equals low species richness because th superior species
outcompete everything.
When disturbance is
extremely high, you would expect species richness to be low, because these
disturbances are frequent enough and happen so much that its not jsut the
dominant species tha are being eliamted from the system, but everything else.
So what we expect to find is Th
SLIDE 37
For smaller bolders, frequently pusehda round by the waves,
and they face a lot of disturbance. Larger borders don’t move as much. He found
that large boulders, they tend to have fewerspecies on them, because the
dominant species on these boulders were able to exlude other speices
For the smaller boulders, frequernlty rolled around, he
found very few speices as well because of the constant disturbance was so high
hard for any species to establish
Finalyl for the intermediate thes had the highest amounts of diversity.
One of the problems with the intermediate disturbance
hypothesis is its a pretty simple model. And it doesn’t capture a lot of
realism
SLIDE 38
So Huston added another dimension to it, competitive
displacement –
SLIDE 39
The species in blue being the competiviely superior species These
are equilibrium condtions where no disturbances are occurring for low
prodiuctivty and high productivity.
We can expt that the superior species is able to reach its
carrying capacity at a faster rate within the high productivity sites versus
the low productivity sites. So this rate of growth for the competitively
superior species is competitive displacement?
But when we start seeing periodic disturbances (indicated by
the arrows in the system) this delasys the rate of superior to reach its
carrying capacity, lessenoing its chances of exluding inferior species.
But the thing is, when disturbance is too high within a
system, only a few good colonizers are able to establish/. We incorporate this
idea of competitive dispalccement then....
We would expwcr speies diversity to be the highest when the
frequency of disturbance and also the rate of displacement are at low levels. And
the reason for this is because the superior competitor will be kept in check by
these disturbances that are frequenct enough that kit keeps the population from
competibiely exluding other species.
And there are 2 different scebnarios where we see low
species richness. So in the first scenario, is when the distiurbance is high and the
displacement is low, and this is because the superior competitor can’t reach
its carrying capacity, and as a consequence can’t exclude other species. But
because the disturbance is so high than earlier, other species will not be able
to survive in that environment either.
And the second instance is when the disturbance are so
infrequent to the point where the competitibely superior species is able to
reach its carrying capacity and exclude other species.
So the important thing to take away from this dynamic
equilibrium mode is that this ratio between teh growth rate of the dominant
species and the rate of disturbance occurring and how they help each oher.
The thing with these theories is that there is some
competigtive underlying hierarchy, the diea that species are competitively
superior to others.
SLIDE 44
lOTTERY model says species have similar interaction strengths
and population growth rates....whats more important is the abiliiyy of these
species to quickly disperse once disturnace occurs to take advantage of an
environment recently made available.
SLIDE 45
This was conducted in the great barrier reefs of Australia. The
diversity in these reefs is very high. Why are there so many species that can
co exist with each other in such a small spaceÉ
SLIDE 46
One of the more important things behind this idea is that
its really a lottery system, where the fishes will produce many highly mobile
javelins that can take advantage of the space available. Ad long as one species
is able to win thje lottery (establish and reproduce) then it will continue to
reproduce and enter the lottery again. This is how the lottery allows co
existence.
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