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Community interactionsCommunity interactions
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2.
In ecology, a community is the
biotic component of an ecosystem.
It consists of populations of
different species that live in the
same area and interact with one
another.
The five main forms of interaction
between population. The forms
are: 1. Mutualism 2.
Commensalism 3. Parasitism 4.
Competition 5. Predation.

3.
Populations Interactions
Species
- A
Species
- B
Name of the
Interaction
+ + Mutualism
+ 0 Commensalism
+ - Parasitism
- - Competition
+ - Predation

4.
1. Mutualism:
It is an interaction that confers
benefits to both the interacting
species.
Examples of mutualism are:
a. Lichens represent an intimate
mutualistic relationship between a
fungus and photosynthesizing
algae or cyanobacteria.

5.
Here, the fungus helps in the
absorption of nutrients and
provides protection, while algae
prepare the food.

6.
b. Plants need help from animals
for pollination and dispersal of
seeds. In return, plants provide
nectar, pollens and fruits to the
pollinators.

7.
For example, the female wasp uses
the fruit not only as an oviposition
(egg-laying) site but uses the
developing seeds within the fruit
for nourishing its larvae.

8.
The wasp pollinates the fig
inflorescence, while searching for
suitable egg-laying sites. In return,
fig provides the wasp some seeds
as food for the developing wasp
larvae.

9.
2. Commensalism:
It is the interaction between two
species, where one species is
benefitted and the other is
neither harmed nor benefitted.

10.
Examples
a. Barnacles growing on the back
of whale gets benefitted to move
to different locations for food as
well as shelter, while the whales
are neither benefitted nor
harmed.

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b. Egrets always forage close to
where the cattle are grazing.
Because, the cattle egrets are
benefitted by the cattle to detect
insects as the cattle stir up the
bushes and insects are flushed
out from the vegetation to be
catched by cattle egrets.

12.
c. Sea anemone has stinging
tentacles and the clown fish lives
among them.
The fish gets protection from
predators, which stay away from
the stinging tentacles. The
anemone does not appear to derive
any benefit by hosting the clown
fish.

13.
3. Parasitism:
It is the mode of interaction
between the two species in which
one species (parasite) depends on
the other species (host) for food
and shelter and damages the host.
In this process, one organism is
benefitted (parasite), while the
other being harmed (host).

14.
(i) Adaptation Methods of a
Parasite:
(a) Parasite is host-specific in a way
that both host and parasite tend to
co-evolve.
(b) Loss of unnecessary sense
organs.
(c) Presence of adhesive organs or
suckers.
(d) Loss of digestive system.
(e) High reproductive capacity.

15.
(ii) The life cycles of parasites are
often complex, involving one or
two intermediate hosts or vectors
to facilitate parasitisation of its
primary host.
For example
(a)Human liver fluke
(b)Malarial parasite

16.
(iii) Majority of parasites harm the
host. They reduce the survival,
growth and reproduction of the
host. They reduce its population
density by making it physically
weak.
(a) Ectoparasites feed on the
external surface of the host
organism for food and shelter.

17.
(b) Endoparasites live inside the
host’s body at different sites like
liver, kidney, lungs, etc., for food
and shelter.
(c) Brood parasitism is a
phenomenon in which one
organism (parasite) lays its eggs in
the nest of another organism.

18.
Brood parasitism
Endoparasites
Ectoparasites

19.
4. Competition:
Competition occurs when closely
related species compete for the same
resources that are limited:
a. It can be best defined as a process in
which the fitness of one species
(measured in terms of its ‘r’ the
intrinsic rate of increase) is
significantly lower in the presence of
another species.

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b. It is a type of interaction, where
both the species suffer.
c. Some totally unrelated species
could also compete for the same
resources
c. In interspecific competition, the
feeding efficiency of one species
might be reduced due to the
interfering and inhibitory presence of
the other species.

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5. Predation:
It is an interspecific interaction,
where an animal called predator
kills and consumes the other
weaker animal called prey. This is a
biological control method .
Important roles of predators are:

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(i) They keep prey population
under control.
(ii) They help in maintaining
species diversity in a community
by reducing the intensity of
competition among prey species.
(iii) In absence of predators, prey
species could achieve very high
population densities and cause
instability.

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(iv) When certain exotic species
are introduced into a geographical
area, they become invasive and
start spreading fast.
(v) If a predator is too efficient
and exploits its prey, then the prey
might become extinct.
(vi) Prey species have evolved
various defence mechanisms to
lessen the impact of predation.

24.
Some species of insects and frogs
are cryptically coloured
(camouflage) to avoid being
detected easily by the predator.