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October 20 2008
We finished discussing the importance of chemical factors in determining herbivory from taking
effect. All organisms die and decompose (pig example) and the importance of community
ecology that occurs when things decompose. There are chemical factors that prevent the rapid
decay as well as preventing organisms being feasted upon while they are still alive. We talked
about plants predominantly (alkaloids). If there are pharmacological affects that will affect the
feasting animal then they won’t eat it i.e. caffeine, nicotine, and morphine will have quite
sophisticated affects on the CNS. They are all addictive as well as you know. There are 1,000s
of chemicals that are routinely produced by plants.
Microbes, fungi, algae, and animals also produce chemicals to prevent feasting by predatory
organisms on them. The most sophisticated arsenals are made by plants probably because they
can’t run away from anything. Saplings have to have some defence or they will be eaten
completely. We used the example of the Moose and how it wouldn’t eat the whole meadow.
The plants will mount a defence because they will produce a higher amount of chemicals to keep
from being eaten. The responses can be rapid and happen within hours and over several days in
most plants the differences can be measured to repeal feeding in those environments. In
BGYB50 we talked about how plants in this environment here probably wouldn’t be affected by
herbivory. Most biomass produced by plants stays put. We talk about transit time of biomass
and how fast that can be.
Aquatic ecosystems are usually not endowed with chemical defence and as a result they are
predated upon by others. They are eaten very quickly. Organisms that perform photosynthesis
will channel the majority of their biomass into the food chain. On land the majority of biomass
will not flow through this food chain but most of it will fall prey to the detritol food chain. It
will take longer for the maggots to begin to invade a plant corpse if it is full of these chemicals.
The sophistication that has evolved in the 500,000 plant species (most haven’t been named in
Latin as of yet 50%). There are millions of chemicals out there that differ a little. They are all
based on aromatic chemistry that has 1 or several Benzene rings in them. You will always find
nitrogen bound to carbon to the ring itself or by a side-chain. A methyl group next to nitrogen is
common. There is a striking similarity between Hordenine (Barley plant) and the chemicals in
your body i.e. Dopamine. The plants know when something is feeding on them and they will
produce a feeding repellent. Plants can produce many of the same chemicals (neurotransmitters)
in our bodies. If they don’t directly produce these neurotransmitters then produce chemicals that
are similar i.e. Epinine and Hordenine and they mimic the acts of Dopamine (different by only 1
methyl group). If you eat any of these plants your body will feel that it wants more because your
gut is confused but after a while, as it feasts longer, the other neurotransmitters will make you
feel queasy before you have actually eaten too much. There are many papers that are written
BGYC61H3F.October.20.2008 Lecture 6 1
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about this subject. If plants didn’t know how to defend themselves we wouldn’t have any
meadows, shrubs, forests, etc.
Smart pharmacological researchers know these facts and they prospect for plants in the wild to
produce these compounds when they are infected by viruses and bacteria, when they basically
have the flu. They test to see how good the plants are fighting off the bacteria/viruses. 90% or
more of our drugs come from the plant world.
This plant is stinging nettle and it is a weed. You get a rapid and pronounced response on your
skin that is a histamine response. Not just indigenous histamine in your cells but in the leaves of
the plant. The ‘trichomes’ or hairs are loaded by chemical cocktails i.e. histamine and
acetylcholine. They also have formic acid that helps the penetration of histamine into your skin
and the response is similar to hay fever. You take an antihistamine if you encounter this plant in
the wild. It is fascinating that plants out there are capable of producing sophisticated
neurotransmitters. It has metabolic machinery in there to make all these chemicals. If this plant
is experiencing stress i.e. feeding animals, it will produce more so the next animal that comes
along will be affected. The response is so immediate the animal will walk away and feast on
something else. People die from the histamine response when stung by an insect/bee. In the
wild a similar response would occur if deer were to eat a large amount of this herb. Intelligent
animals like deer or monkeys know this information and they tell each other about it.
There are some plants like the ‘Bulls Horn Acacia Plant’ that produces spines (not thorns).
Spines are highly modified leaves which become prickly. The thorns on the roses are not
actually thorns just so you know. It has fascinated chemical ecologists for a long time. These
are wide spread in tropical forests and don’t seem to be producing alkaloids at all. They don’t do
it because they don’t have to because these trees have a symbiotic/mutalistic association with
ants that live inside them. When the plant experiences herbivory pressure the ants come out. It
does cost the plant some money i.e. sweetness/sugar/nectar that the ants eat internally. The ants
live inside so they are not eaten and they stand guard for the ‘Bulls Horn’. If you want to find
the function of something find an organism (mutant) that doesn’t have that feature and then you
might find the importance.
How much carbon/energy flowing through an eco system and how fast? We have a much more
rapid flow of biomass than any other terrestrial eco system.
The other domain is with bacteria that could live in extreme environments i.e. ‘Yellowstone
National Park’. These are water puddles near the boiling point (on overhead) and they go right
down to the earth’s crust. You can get a serious burn just by reaching in there. These contain
many chemicals that come up from the earth’s mantle. There is also a high amount of nickel,
zinc, titanium, chromium, etc. coming up from the mantle. There are highly specialized bacteria
in there as well. These are fairly young bacteria that are in here but the fact that we have them
now doesn’t mean we didn’t have those eons ago. What is interesting is what they eat which is
just about anything.
BGYC61H3F.October.20.2008 Lecture 6 2
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Here is an example of bacteria that can break down the Benzene ring. We can’t break up the
Benzene ring as humans but some bacteria can. There is a lot of interest in this type of bacteria.
It would be great if we could just bring out bacteria and put them on an oil spill and have them
clean it up, the specialist feeding. Some bacteria can break down the cyanide chemical like we
talked about last time.
You don’t know how bad some of the effects can be if you work in a gas station or pump your
own gas, the fumes are very toxic. There are some organisms that can break this down and they
test this all the time. They are looking for bacteria that break chemicals down that do harm to us.
There are bacteria that break down PCBs and dioxins etc.
Three Theoretical Functional Response Curves: with respect to how an organism that feasts
upon something is feasting on that something as a function of the food/prey density. Prey isn’t
just animal prey it can be plant density or algae density in water. There are 3 major types; type
1, type 2, and type 3. All three curves level off at medium to high prey density.
Type 1 is a linear response to the type of food that is eaten with increasing density of food
available. Lineally it eats more and more until it is satisfied and then it plateaus.
Type 2 looks more satiable followed by a plateau. This is the most common in nature. It is
curvy linear followed by saturation. You have seen this before and it is called the Nicholas &
Type 3 is found in highly involved, intelligent, socially living animals (monkeys, birds, rats,
mice, etc.) and they have a sigmoidal response curve with response to food that is available and
what gets eaten. Intelligent animals like humans, primates, most birds etc. are not going to eat
something that is fairly rare. Only once the availability of food becomes higher will they eat it.
They then eat it and it takes off rapidly.
You know that the shape of the curve and onset of saturation will be a strong function of
Type 1 this is the Whale Shark which is the largest shark in the world (it is a fish). It is a filter
feeder which means it opens it mouth and swims and anything that goes into its mouth is eaten.
This isn’t always good because they take things into its body that can kill it. It feeds on little
things like plankton and shrimp. This will show a linear dependence on the density of the
organisms that are there. When density gets larger it will close its mouth and be saturated.
A Functional Response by Moose: this is an example for moose feeding in herbivory in
Graph: Here is the curve named after Nicholas & Minton. In enzyme kinetics you look at the
rate of transmission. In ion transport research we use the curves and we look at the plasma
membrane level at the function of the intake of the iron across the membrane. The Vmax is the
BGYC61H3F.October.20.2008 Lecture 6 3
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