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Module 1: Ecological Interactions and Energetics

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Negative Interaction

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Today we will move forward with our discussion on Ecological Interactions and look at
negative interactions.
Before we begin, let us summarize what we had learnt in the previous lecture. We had
looked at 6 different kinds of ecological interactions. The first is competition. In the case
of competition, the first organism is harmed the second organism is also harmed. This is a
negative interaction and we will explore it in greater detail today.
The second one is amensalism. In the case of amensalism, one organism is harmed; the
second organism does not suffer a benefit or a harm. This is a negative interaction because
at least one party is getting a harm. We will also look at amensalism today. The third one
is Exploitation. In the case of exploitation, you have a harm to the first organism and a
benefit to the second organism. Because at least one party is getting a harm, we call it a
negative interaction or an inharmonious interaction.

We look at exploitation today and various forms of exploitation such as predation,
parasitism and so on. Next is neutralism. Neutralism is an ecological interaction where the
first organism is not harmed and the second organism also is not harmed. So, none of them
is getting a benefit or a harm. So, there is no impact on any of these two organisms because
of the interaction, but because there is no harm, we will call it as a harmonious interaction.
Next one is commensalism. In the case of commensalism such as the egrets that were
feeding along with the buffalos as we saw in the previous lecture, there is one party that
does not get any harm or benefit that was the buffalo in our example and there was one
organism that was getting a benefit that was egret in the example.
So, because none of the parties is getting a harm, we call a harmonious interaction and the
last one is mutualism in which there are two parties that are getting benefit. Both of them
are getting benefit and then we also saw it looked at a variant of mutualism that is known
as Protocooperation.
(Refer Slide Time: 02:35)

In today’slecture, we will focus on the inharmonious interactions. So, what is harmonious?
What is what is inharmonious? Harmonious interactions are positive ecological
interactions where none of the participating organisms is harmed; as you saw in the
previous class and in the case of inharmonious interactions; these are negative ecological
interactions, where at least one of the participating organisms is harmed; which we will
consider in today’s lecture.

(Refer Slide Time: 03:03)

What are the main kinds of non-harmonious or inharmonious ecological interactions that
we see in nature. Here again we can divide them into intraspecific interactions and
interspecific interactions. In the case of intraspecific interactions, we have interactions
between individuals of the same species. Intra is within, specific is within the same species;
and here we have the examples of intraspecific competition and cannibalism.
Intraspecific competition is where members of the same species are competing against
each other. Intra is same, specific is species; same species competition. For example one
human being competing against another human being, one chital competing against
another chital, one tiger competing against another tiger. So, these are intraspecific
competitions.
The second one is Cannibalism. Cannibalism is a situation in which one organism eats up
another individual of the same species. For instance, a good example is the black widow
spider. After mating the female kills and eats up the male. That is an example of
cannibalism. Here also one organism is getting harmed. It is getting killed and eaten. It is
an inharmonious interaction and it is intraspecific because the male and the female back
widow belong to the same species.
Next is Interspecific interactions, which is between two species. One is interspecific
competition where one animal or one organism is competing against another organism of
a different species. Examples include, chital competing with sambar or chital competing

with hares that are found in the nature. These will be the examples of interspecific
competition or say a tiger that is competing with a leopard. This is interspecific
competition. Another example is Parasitism. Parasitism is where one organism acts as a
parasite on the body of another organism. Third one is Predatism or Predation in which
one organism eats the member of another species. So, it eats up another organism which
belongs to a different species. That is an interspecific inharmonious interaction.
And the fourth one is Amensalism. Amensalism is a process in which one organism is
harmed and the second one does not suffer any benefit or any harm. These are all the
inharmonious interactions that we look in greater detail in today’s lecture.
(Refer Slide Time: 05:59)

.

We begin with competition. Competition is defined as the ecological interaction in which
individuals explore the same ecological niche. When we say explore the same ecological
niche, niche is the position or the role of an organism. For instance, if you have two
insectivorous birds, so there are two birds that are feeding on insects. Their niche is the
same; you can have an even more precisely defined niche. There are two birds that are
eating ground dwelling insects. So, these are exploring the same niche or their ecological
niches part partially coincide. When we say partially coincide, we mean that there is one
bird that is eating insects that are found in trees and also on the ground and there is another
bird that is eating the insects that are found on the ground.

In this case both the niches are partially coinciding because both the birds are exploring
the same niche that is that of the ground even though their niches are not completely
overlapping with each other. Competition is the ecological interaction in which individuals
explore the same ecological niche or their ecological niches partially coincide and
therefore, competition for the same environmental resources takes place. There is
competition for the same environmental resources and these resources could be anything
such as food, they could be shelter, they could be physical space, they could be mates, they
could be access to water, they could be access to sunlight so on.
There is competition for the same environmental resources. We typify competition as
intraspecific versus interspecific. Intraspecific competition is competition between
members of the same species and interspecific competition is competition between
members of different species. We looked at their examples before; the second is
exploitative versus interference competition.
Exploitative competition is where organisms are exploiting the same resource and
interference competition is competition where organisms are not permitting another
organism to use the same resource even when they are not exploiting the same resource.
A good example of exploitative competition is the situation where there are a number of
animals that are grazing together on the same grassland.
(Refer Slide Time: 08:45)

In this case, there is a piece of grassland and you have a number of organisms that are
feeding on this. There is one animal, there is another animal and then, there is the third
animal. If this animal eats up the grass, if it eats up a majority of the grass, so the grass
that is available to these two animals will be less. Essentially in the case of exploitative
competition you are exploiting the resources in such a way that you are overshooting your
own share, so that the share of others reduces. This is exploitative competition. In the case
of interference competition, you can have a situation in which you have the same
grassland.
(Refer Slide Time: 09:31)

And you have these same herbivores that are waiting to reach the grassland. So, let us
reduce the size of this grassland. Here you have the grassland, here you have the herbivores
and here you have a dog that is not allowing them to get into the grassland. This is an
interference competition. Even though this dog is not using the grassland, this dog is not
feeding on the grasses, but it is interfering with the ability of the herbivores to reach into
the grassland.
This is an example of interference competition. Another competition goes by the name of
apparent competition and we look at exploitative interference and apparent competition in
more detail soon. Let’s see an example for apparent competition.

(Refer Slide Time: 10:33)

You have say a pond and in this pond, you have these two species of fishes; the red fish
and the green fish. Now, you have say 3 of green fish and 3 of red fish. Suppose the red
fish multiplies itself very much. And in this situation, suppose you had a predator. That
predator say is a bird. So, you have a bird that is coming and feeding on the fishes. Now,
in this case, because the number of red fishes and the number of green fishes are one and
the same, say 3 fishes. So, equal number of these animals are removed from the system,
but now, if the red fish multiplied itself and it became in place of 3, it became 6; now what
will happen now this bird will have an access to more amount of food because it has more
number of red fishes that are there in this pond. It has more amount of food. Probably, it
will be able to reproduce in a much better way. In that case it reproduces and now in place
of one bird, you have two birds. What happens now? You have two birds and these two
birds will again require fishes to feed.
When that happens, these birds will not only be consuming the red fishes, they will also
be consuming the green fishes. Because in this pond you had the red fishes, they increase
their number leading to an increase in the number of predators and those predators are now
predating upon the green fishes as well.
Essentially what these red fishes have done is that they have created a situation in which
the green fishes are getting harmed even though that was not their intention, even though
they did not want to do that, even then just because they increase their numbers, so the

green fishes are getting harmed and such a scenario goes by the name of apparent
competition. We will locate apparent competition in more detail in a short while.
To recap competition is the ecological interaction where individuals explore the same
ecological niche or their ecological niches partially coincide and therefore, competition
for the same environmental resources takes place.
(Refer Slide Time: 13:07)

.

Now, we will look at some examples. Let us look at these Penguins. We went to South
Africa and there is a place known as the Boulder Beach. On this boulder beach, we have a
colony of penguins, so these are African penguins that are found in South Africa and most
of these penguins were either having an egg or they were even having a baby. This was
post their mating season. If you observe these penguins, they are at a certain distance from
each other and this distance is what we refer to as the pecking distance. If these birds were
any closer, they would start biting off the other bird because each bird requires a certain
amount of space. So, here we have a competition for an environmental resource which is
space on this beach and they require this space, so that they are able to make their nest, so
that they are able to lay their eggs, so that their babies come out and their babies are able
to survive and become the next generation. To do that, you require a piece of this sandy
beach. Now this sandy beach is not available in plenty, the number of birds is much greater
than the amount of sandy beach that is available. What they do? They compete for the
resources. The best bird will get the best location and it will drive off the other birds to

those locations that are not that good and if any other bird tries to come within its own
territory, it will start to bite that bird or it will start to peck at that bird. Let us now see how
that looks like.
What these birds are doing here is that when they come close together, they peck at each
other. They show a behaviour that is a behaviour of competition. They want to displace
the other one out of their own territory and then they are also showing a behaviour, or a
ritualistic behaviour in which this bird which has become dominant. It will take its beak
upwards, it will start making a display, it will show off its neck and it will make a noise,
whereas, these birds that have become recessive so they are not as competitive as this bird.
So, this one is dominant, this one is recessive.
In this situation, this bird will show off a display that yes I am the boss here, this is my
area, you cannot come into this area and these birds will keep their heads down and they
will act in a submissive manner. We look at this clip once more. So, just keep an eye out
for the dominant and the recessive behaviours when these penguins are fighting for the
territory. So, the left bird, it took its beak above and this one kept it down.
(Refer Slide Time: 16:53)

Another example is the example of these black bucks that are fighting for the mate. So,
here we have two male black bucks here. We have a female black buck and these two black
bucks are fighting to have access to the mate. So, in this case the resource that they are
fighting for is not space. You have ample space here. It is not grasses. You have ample

amount of grasses here, but they are fighting for this resource which is the mate. So, how
do these animals fight?
This is how they will fight. So, they will use their horn. They have these long antlers and
they will use these antlers to fight against each other. This one is closer to the female and
this one is able to displace the other one away from the female. These are black bucks that
are fighting for the mate. Now, when such a situation happens, when there are organisms
that are fighting for a resource, in the case of conservation this can have very significant
consequences and one example of that consequence is the phenomenon of habitat
displacement.
(Refer Slide Time: 18:23)

Now, what happens in the case of a habitat displacement. In this example, what you are
seeing is that you have these black bucks that are there in this grassland. Now these black
bucks feed on the grass and so, they require the grasses to be there and this is one of the
best suited locations that they can have to survive. They have ample amount of grasses,
they have some trees to protect them from the sun if need be and they happily living here.
Here you have let us say that this area also adjoins say a rocky place. So, you have here a
number of grasses and grasses are there on the flat land, you also have some trees that are
providing them with shade and then, you have these rocks and then, you have the black
bucks. The whole area is being used by the black bucks.

Now what happens is, if you have say people who bring in cattle into this area, so they
bring in this cattle. Now, if cattle come into this area, they would also be herdsmen that
would accompany the cattle. So, you will have people who come with their cattle and they
want their cattle to graze on these same grasses because these grasses are not only
nutritious for the black bucks, they are also nutritious for the cattle and the more nutritious
grasses the cattle get, the more amount of milk they would produce. So, the farmers will
be happy. In that case what happens is when the farmers or when the herdsmen come with
their cattle to this area, they probably would also come with some dogs and other stuffs.
They would either kill off these black bucks or they would force these black bucks to move
somewhere else. Now this is the most prime habitat that the black buck has.
The black buck has access to food, it has access to shelter, there are also a few water bodies
here. This is the most prime habitat, but then when the herdsmen come with their cows,
they will displace away these black bucks. We will have a situation in which these black
bucks will get into this location which is a sub prime location and this area will now have
the cattle in place of the black bucks.
In this case here you have the prime habitat and in this area you have the sub prime habitat.
Now why is that so? Because this area is the prime habitat, because it has flat terrain, it
has ample amount of grasses, it has some trees for shelter between the summer season, it
also has some access to water. This area is now a sub prime habitat? Why?
Because this area is say rocky or this area does not have enough grass or say enough food
or water or maybe this area does not have trees for shelter. Now, in such a situation, we
observed that these animals are getting displaced out of their habitat into a subprime habitat
and this thing is known as habitat displacement. In nature what we observe is that, in this
area you have these black bucks and they are competing against each other. Probably they
will also be having some sambars , some chitals and some other such animals nearby.
For instance if you have sambars in this area, you will have a phenomena that is known as
niche differentiation in which you will find that the black bucks are most suited for these
grassland habitats and the sambars are more suited for these rocky areas. So, they will
automatically make use of both these niches, but when humans get into this picture, they
tend to displace these animals from their habitat and to conquer those habitats.

When we say that man is able to conquer the earth, man is able to conquer the forest and
we convert forests into our... into areas that we want in the form of farmlands or in the
form of habitations. This is what is happening. This important phenomenon of niche
differentiation and habitat displacement together with the phenomena of competition is
very much required also for conservation.
(Refer Slide Time: 24:07)

.

Let us look at different kinds of competition. We differentiate between exploitative
competition and interference competition. Now, remember exploitative competition is
competition where you have a number of animals that are competing for the same resource.
This is what we had discussed before, in the case of exploitative competition. You have
all of these herbivores that are competing for the same amount of grassland. In the case of
interference competition, you have some animals that are not allowing others to make use
of the same piece of grassland.
Exploitative competition is also called a scramble competition whereas interference
competition is known as contest competition. In the case of exploitative competition there
is a scramble for resources. Everybody wants to use the same resource. In the case of
interference competition, everybody is contesting for the same resource. They are not
using this resource, but there is only a contest.
Competition is exploitative when species or individuals compete for the same limited
resource that is herbivores that are fighting for the same piece of grassland and competition

is interference when species or individuals deplete others resources by interferences such
as aggressive displays or fightings. You have a dog that is barking and so is not allowing
the other animals to get inside. In exploitation organisms use of resources directly. It is no
longer available for use by others. Essentially if one cow eats up most of the grass, this
grass is not available to be used by other cows. The organisms are using up the resources
directly.
In the case of interference, one organism prevents others from using the resources. So, it
is not using the resources itself. When we look at this example of the dog, so here we have
this dog that is not using the grassland. It is just preventing the cows or the buffaloes or
the cattle from entering into this grassland.
We have this phrase in english , “a dog in the manger”, which means that you have a dog
that is sitting on a pile of hay, it is not eating up that hay and it is not allowing the other
organisms to eat up that hay. Now, there is no direct contact or conflict between the species
or individuals in exploitation. There is no direct contact or conflict because when these
cows are competing against each other, they are not competing personally against each
other, they are just eating up the resources. There is no direct contact between both of
these, but in the case of interference competition, there is a direct contact or conflict
between the species or individuals in interference.
In the case of the dog and the cows, the dog is directly conflicting with the cows.
(Refer Slide Time: 27:09)

Further, competitive ability and exploitation is the rate of resource consumption.
Competitive ability of one cow can be defined as the rate at which that cow is eating up
the grass. The more amount of grass it eats up per unit time, the more is its competitive
ability and the less amount of grass will be available to be used by the other cows. In the
case of interference competition, competitive ability in interference is the ability to put on
aggression or fight. In the case of interference competition, the more amount of fights you
can put up, the more amount of aggressive displays that you can do, the more you can bark,
the more you can use your horns to keep others away, the more is your competitive ability.
Pure exploitative competition can be modeled as affecting the carrying capacity. When we
see carrying capacity, carrying capacity is how much amount of resources are available
and how many individuals can survive on that amount of resources. For instance, if you
have a piece of grassland and if you sow some grasses that can grow very fast and are more
nutritious, so more number of cows or more number of herbivores can be accommodated
or sustained by that piece of grassland.
We will say that the carrying capacity is increased. On the other hand, if you have a cow
that is eating up all the grasses, so less amount of grass is remaining for the other animals.
So, we will say that the carrying capacity is not going down. Pure exploitative competition
is where you do not have any amounts of interference. Pure exploitative competition can
be modeled as affecting the carrying capacity. It is as good as you reduce the carrying
capacity of the grassland and pure interference competition can be modeled as affecting
the rate of increase per individual.
Basically when the cow eats grass, so it is using that grass or that energy or those nutrients
to build up its own body and also to give rise to the next generation of offsprings. Pure
interference competition can be modeled as a reduction in the ability of the animals to use
the resource. Even though you have the resource, you are not able to use it.
For instance, this can be modeled as follows. Suppose 100 kgs of grass was required to
give rise to an offspring, now you can say that in place of 100 kgs of grass you will require
say 200 kgs of grass. There is an impact on the rate of increase per individual or you can
say that earlier you were having an offspring every 6 months. Now, there will be an
offspring not every 6 months, but say every 9 months. That would be a way of modeling
the situation.

For pure exploitative competition, the relation between the rate of change per individual
of one species and abundance of the second is non-linear. Now in the case of exploitative
competition, the rate of change per individual of one species and the abundance of the
second is non-linear. What do we mean by that? The more number of individuals that you
have of a species, so for instance, there is a piece of grassland that is being eaten by cows
and buffaloes.
If you have more number of cows, then what is the rate of increase of buffaloes? How does
it impact that? If you did not have any cows, so the buffalos were having access to all the
grass. They would use that grass to increase their weight or to increase the total amount of
biomass that is available in the form of their bodies and in the bodies of their offsprings.
You put in more number of cows and the amount of grass that is available for the buffaloes
is less. The rate of increase will reduce, but then the relationship between both of these is
non-linear, but in the case of interference competition the relation between the rate of
change per individual of one species and the abundance of others is linear.
The more number of say dogs you have in your grassland, the lesser would be the rate of
increase in the cows or the cattle and this relationship will be a linear relationship.
(Refer Slide Time: 31:49)

.

Let us look at some examples of exploitative and interference competition. An
intraspecific exploitative competition is an organism over grazing on a land shared by

several individuals of the same species. For instance you have a grassland that is being
grazed by a number of cows. In this case, every cow is doing an exploitative competition
against every other cow that is present on the same piece of grassland. This is an
intraspecific competition and it is between animals of the same species.
Next is interspecific competition. In this case, you have the same piece of grassland that is
being grazed by cows as well as buffalos. In the interaction between the cow and the
buffalo, one cow and one buffalo will be an interaction of exploitative competition, which
is interspecific in this case because you have cows that are competing with buffalos,
members of another species or another example is canopy trees of several species
competing for the available sunlight. What do we mean by this?
(Refer Slide Time: 33:03)

.

In a forest or in any piece of land, the amount of sunlight that is available is limited. So, if
you have a tree. This tree is now casting a shadow. This is the shadow region and if you
have saplings here of different species, so all of these species are now not able to get access
to the sunlight because of the presence of the first tree. Because you have this tree of
species 1, these saplings of a species 2, 3 and 4 are also not able to get access to the
sunlight. This is an example of interspecific, because this concerns two different species.
This is inter specific competition because they are competing for the same resource and
this is an exploitative competition because the more the first species is consuming, the
lesser is available for the rest. For instance, in place of this canopy if you had a smaller

canopy say if this was the canopy. In that case the amount of the shadow region would
have been lesser and so this individual would have survived.
This is an example of an inter specific exploitative competition. If you look at interference
competition, the example in the case of intraspecific competition is an animal that is
showing territorial behaviour to its conspecifics. What does that mean?
(Refer Slide Time: 35:05)

When we looked at the penguins and there was a penguin that was not allowing the other
penguin to use that resource, now it is also possible that in place of using. Suppose there
is a penguin that requires this much space, but it is also possible that it shows an aggressive
behaviour for this much of a space. In that case the penguin does not require that much
amount of space, but it is not allowing others to make use of that space. This will be an
example of an intraspecific, because there is one penguin that is competing against another
penguin a member of the same species.
It is intraspecific interference competition interference because they are both directly
involved with each other. There, this interaction is one on one and it involves aggressive
displays, it involves fighting and in the case of interspecific interaction, we can have
allelopathy. What is allelopathy? Let’s take the same example of the tree in the forest.

(Refer Slide Time: 35:55)

You have this tree and say the leaves of this tree when they come down. When they die
off and they come down here, they release some chemicals into the soil and those
chemicals do not permit saplings of other species to thrive.
Because of these chemicals these saplings would die off whereas, the saplings of their own
species would survive because they are resistant against their own chemicals. This would
be known as allelopathy. Another good example of allelopathy is what we saw in the
previous lecture.
(Refer Slide Time: 36:45)

.

You have this petri dish and you had these fungal colonies of penicillin or penicillium and
you had these bacterial colonies and the bacterial colonies that were close to the
penicillium colony because of the impact of penicillin, they were dying off, they were
lysing off. Antibiotics are some chemicals that are released by one species to kill off or to
retard the growth of members of another species.
Thisis also an example of an inter specific. It has two different species; fungus and bacteria
interference competition. What does interference competition mean? Because in this
particular example the colony of fungus is only using up this amount of area on the agar,
it is not using this area, but still it is not permitting anybody else to come here; very much
like the situation of our dog that was preventing other animals from getting into the
grassland. This is an interspecific interference competition.
(Refer Slide Time: 38:03)

Now, apparent competition as we saw before is an interaction between two prey species
with a common predator. In this case, there are two prey species that are competing against
each other just because you have a common predator. You have for instance chital and
sambar and so, if the number of sambars increases, so tigers would get more amount of
sambars.