Biotic Communities in Ecology

Pritam Sharma Abhimanu IAS

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM..

Environment &

Ecology

COMMUNITY ECOLOGY -SYNECOLOGY

WHAT IS A BIOTIC COMMUNITY?

As we know that a community is the third  level in the hierarchy of Biological

organization and in ecology it has a precise meaning referring to a group of

organisms living on the same habitat but belonging to the different species,

interacting with each other.

In short, a biotic community is an interaction among the organisms of two

different populations living on the same territory.

Why Biotic community?

As we already know that no habitat in this nature

contains the individuals of only one species. In fact, a population of a single

species cannot survive by itself because there is always an interdependence of

one form of life on another at least, for food; any species requires one more

species on which it can feed. Even Plants cannot survive on their own, for they

also require microbes to break down the organic matter and pollinators

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

for the sake of pollination to disperse their pollens onto different flowers.

This simply means that the mother nature is an interconnected whole as the life

of every organism is significantly influenced by that of all others around it.

This was what a British Biologist of 19

th

 century illustrated it so beautifully

when he said that:

“ Glory of Britain is due to her old maids as the healthy Britons are nourished

by roasted beef: beef supplying cattle feed on grass: Grass is pollinated by

bees: bee nests are destroyed by field rats: the number of rats depend upon

the number of Cats. Since Cats are reared by old maids, the old maids thus

determine the supply and availability of beef.”

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

From the above illustration, we can thus conclude that in nature there is always

an interdependence among the organisms in a given habitat such that a kind

of living community (biotic community) comes into being.

This natural association of the interdependent populations of different species

inhabiting a common environment or habitat as a viable, self-contained unit is

called, a biotic community, or

biocoenosis

In short, in the simplest words, a biotic community may be considered as a

multi-species population.

CHARACTERISTICS  OF A BIOTIC COMMUNITY

In nature, each biotic community is known for its unique characteristics which

differentiates it from other biotic communities. Some of these features may be

discussed as below:

1. Species composition:

Each biotic community has its distinct species of animals

and plants which constitute the species composition of the particular

community. For example, in a grassland, the species of animals may be

herbivores such as Zebras, Giraffes, Deer etc, and the species of carnivores

can be Lion, Tiger or Leopards etc. Among plants, it may be shrubs, herbs or

grasses and no Trees. Similar is the case of an ocean where the species

composition may be entirely different.

2. Dominant Species:

In every biotic community, there would be some species

which are dominant over the others on whose basis that community is named.

For example, in a forest community the dominant species may be tall trees of a

particular species. For example in a grassland, it is the grasses that are

dominant over all other herbaceous plant species. However, the communities

are also named after the environmental factor say, a desert or marine

community.

3. Stratification: It refers to the vertical layering of vegetation in a community

accompanied by an associated animal life. Similarly, in a Lake or other

aquatic biotic community, we have surface and bottom dwellers depending

upon the penetration of light through stratified layers of water.

MPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

3. Key stone and Link species:

In every biotic community, there are some

species which are so important that they pose a profound impact on the

abundance of other species in the community. For example, in a tropical rain

forest, different species of fig tree a ct as a keystone species.

Similarly, the Beavers in an aquatic ecosystem act as keystone species as they

manipulate the aquatic environment by constructing dams and construct pools

that act as  a habitat for many other species. The significance of a key stone

species can be explained with the help of the famous

Rivet-Popper hypothesis

The Link species on other hand refer to those species in a biotic community that

act as a link between a number of other species or play a vital role in the

absorption of minerals like

Mycorrhiza.

Insects & Birds act as link species.

4. Ecotone and Edge effect:

An ecotone is a transitional area between two or

more communities. It contains the species from both the communities. It is always

noted for the abundance of organisms or species.

This phenomenon is referred to as Edge effect. The species living in the ecotone

region are referred to as the edge species.

For example, a grassland and pond meeting together in a region is called as

ecotone having species living in this area from both the communities.

INTERACTIONS IN A BIOTIC COMMUNITY

Interactions in a Biotic community can broadly be beneficial, detrimental or

neutral (neither harm nor benefit) to one of the species or both.

 To understand them in a better way, let’s assign a ‘+’ sign for beneficial

interaction, ‘-‘sign for detrimental and ‘0’ for neutral interaction and then

try to look at all the possible outcomes of interspecific interactions.

Accordingly, we shall observe that these interactions may manifest themselves in

some of the following forms  such as Mutualism, Commensalism, Parasitism,

Predation, Competition and Amensalism etc.

Lets discuss each of these interactions and seek to know how they actually

operate in Nature….

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

1.

1.Mutualism:

This interaction confers benefits on both the interacting species.

Lichens represent an intimate mutualistic relationship between a fungus and

photosynthesizing algae or cyanbacteria. Similarly, the mycorrhizae are

associations between fungi and the roots of higher plants. The fungi help

the plant in the absorption of essential nutrients from the soil while the plant

in turn provides the fungi with energy-yielding carbohydrates.

The most spectacular and evolutionarily fascinating examples of mutualism are

found in plant-animal relationships. Plants need the help of animals for

pollinating their flowers and dispersing their seeds. Animals obviously have

to be paid ‘fees’ or so called allowance for the services that plants expect

from them i.e. dispersal of its pollen grains. Plants offer rewards or fees in

the form of pollen and nectar for pollinators and juicy and nutritious fruits

for seed dispersers.

2. Commensalism:

This is an interaction in which one species benefits and the

other is neither harmed nor benefited. Say for example, an orchid growing as

an

epiphyte

 on a mango branch, and barnacles growing on the back of a

whale, benefit while neither the mango tree nor the whale derives any

apparent benefit from the growth of such second species. The

cattle egret

and

grazing cattle browsing in close association, a sight we are most likely to catch

if we were to live in a farmed rural area, is a classic example of

commensalism.

The egrets always forage close to where the cattle are grazing because the

cattle, as they move, stir up and flush out from the vegetation insects that

otherwise might be difficult for the egrets to find and catch. Another common

example is Clown fish and Sea Anemone.

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

3. Predation:

Besides acting as ‘conduits’ for energy transfer across trophic

levels, predators ecologically play other important roles as well. They keep

prey populations under control. But for predators, prey species could achieve

very high population densities and cause ecosystem instability. When certain

exotic species are introduced into a geographical area, they become invasive

and start spreading fast because the invaded land does not have its natural

predators. The prickly pear cactus introduced into Australia in the early 1920s

caused havoc by spreading rapidly into millions of hectares of rangeland.

Finally, the invasive cactus was brought under control only after a cactus-

feeding predator (a moth) from its natural habitat was introduced into the

country. Biological control methods adopted in agricultural pest control are

based on the ability of the predator to regulate prey population.

4. Competition:

It is generally believed that competition occurs when closely

related species compete for the same resources that are limiting, but this is not

entirely true.

Firstly,

totally unrelated species could also compete for the same

resources. For instance, in some shallow South American lakes visiting

flamingoes and resident fishes compete for their common food, the

zooplankton in the lake.

 Secondly,

resources need not be limiting for competition to occur; in

interference competition, the feeding efficiency of one species might be

reduced due to the interfering and inhibitory presence of the other species,

even if resources (food and space) are abundant.

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

5. Parasitism:

It is an interaction between two species what we call as HOST

and PARASITE. To survive, the parasite develops certain adaptations such as:

the loss of unnecessary sense organs, presence of adhesive organs or suckers to

cling on to the host, loss of digestive system and high reproductive capacity.

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,

human liver fluke

(a trematode parasite) depends on two

intermediate hosts (a snail and a fish) to complete its life cycle.

The malarial parasite called as

plasmodium,

on the other hand, needs a vector

(female Anopheles mosquito) to spread to other hosts.

Majority of the parasites harm the host; they may reduce the survival, growth

and reproduction of the host and reduce its population density. They might

render the host more vulnerable to predation by making it physically weak.

Ecologically speaking, the parasites can be of two types called as

Ectoparasites

and

Endoparasites.

Parasites that feed on the external surface of the host organism are called

ectoparasites. The most familiar example of this group is the lice on humans

and ticks on dogs. The female mosquito is not considered a parasite, although

it needs our blood for reproduction because, it does not live in permanent

association with the human host all the time which is an essential criterion for

being a parasite.

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

In contrast, endoparasites are those that live inside the host body at different

sites (liver, kidney, lungs, red blood cells, etc.).

Brood Parasitism: What is it ?

In some birds, a very fascinating example of

parasitism can be seen what we call as brood Parasitism. Here, the parasitic

bird lays its eggs in the nest of its host and lets the host incubate them. In

nature, it is seen live in case of

cuckoo laying her eggs in Crow’s nest.

 During the course of evolution, the eggs of the parasitic bird have evolved to

resemble the host’s egg in size and color to reduce the chances of the host bird

detecting the foreign eggs and ejecting them from the nest.  This can be easily

observed in nature by watching the movements of the cuckoo (koel) and the

crow in our neighborhood park especially during breeding season….

Thank You

ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM

..

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Biotic communities play a crucial role in ecology, representing interactions among different species sharing the same habitat. This interdependence is essential for the survival and balance of various organisms in nature. Each community has unique characteristics, such as species composition, reflecting the diversity and dynamics of life within it. Recognizing the significance of biotic communities helps us appreciate the interconnectedness of all living beings in an ecosystem.

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Abhipedia IAS Environment & Ecology COMMUNITY ECOLOGY -SYNECOLOGY Pritam Sharma Abhimanu IAS ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 1

Abhipedia IAS WHAT IS A BIOTIC COMMUNITY? As we know that a community is the third level in the hierarchy of Biological organization and in ecology it has a precise meaning referring to a group of organisms living on the same habitat but belonging to the different species, interacting with each other. In short, a biotic community is an interaction among the organisms of two different populations living on the same territory. Why Biotic community? As we already know that no habitat in this nature contains the individuals of only one species. In fact, a population of a single species cannot survive by itself because there is always an interdependence of one form of life on another at least, for food; any species requires one more species on which it can feed. Even Plants cannot survive on their own, for they also require microbes to break down the organic matter and pollinators ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 2

Abhipedia IAS for the sake of pollination to disperse their pollens onto different flowers. This simply means that the mother nature is an interconnected whole as the life of every organism is significantly influenced by that of all others around it. This was what a British Biologist of 19th century illustrated it so beautifully when he said that: Glory of Britain is due to her old maids as the healthy Britons are nourished by roasted beef: beef supplying cattle feed on grass: Grass is pollinated by bees: bee nests are destroyed by field rats: the number of rats depend upon the number of Cats. Since Cats are reared by old maids, the old maids thus determine the supply and availability of beef. ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 3

Abhipedia IAS From the above illustration, we can thus conclude that in nature there is always an interdependence among the organisms in a given habitat such that a kind of living community (biotic community) comes into being. This natural association of the interdependent populations of different species inhabiting a common environment or habitat as a viable, self-contained unit is called, a biotic community, or biocoenosis. In short, in the simplest words, a biotic community may be considered as a multi-species population.

Abhipedia IAS CHARACTERISTICS OF A BIOTIC COMMUNITY In nature, each biotic community is known for its unique characteristics which differentiates it from other biotic communities. Some of these features may be discussed as below: 1. Species composition: Each biotic community has its distinct species of animals and plants which constitute the species composition of the particular community. For example, in a grassland, the species of animals may be herbivores such as Zebras, Giraffes, Deer etc, and the species of carnivores can be Lion, Tiger or Leopards etc. Among plants, it may be shrubs, herbs or grasses and no Trees. Similar is the case of an ocean where the species composition may be entirely different.

Abhipedia IAS 2. Dominant Species: In every biotic community, there would be some species which are dominant over the others on whose basis that community is named. For example, in a forest community the dominant species may be tall trees of a particular species. For example in a grassland, it is the grasses that are dominant over all other herbaceous plant species. However, the communities are also named after the environmental factor say, a desert or marine community. 3. Stratification: It refers to the vertical layering of vegetation in a community accompanied by an associated animal life. Similarly, in a Lake or other aquatic biotic community, we have surface and bottom dwellers depending upon the penetration of light through stratified layers of water. MPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 6

Abhipedia IAS 3. Key stone and Link species: In every biotic community, there are some species which are so important that they pose a profound impact on the abundance of other species in the community. For example, in a tropical rain forest, different species of fig tree a ct as a keystone species. Similarly, the Beavers in an aquatic ecosystem act as keystone species as they manipulate the aquatic environment by constructing dams and construct pools that act as a habitat for many other species. The significance of a key stone species can be explained with the help of the famous Rivet-Popper hypothesis. The Link species on other hand refer to those species in a biotic community that act as a link between a number of other species or play a vital role in the absorption of minerals like Mycorrhiza. Insects & Birds act as link species.

Abhipedia IAS 4. Ecotone and Edge effect: An ecotone is a transitional area between two or more communities. It contains the species from both the communities. It is always noted for the abundance of organisms or species. This phenomenon is referred to as Edge effect. The species living in the ecotone region are referred to as the edge species. For example, a grassland and pond meeting together in a region is called as ecotone having species living in this area from both the communities.

Abhipedia IAS INTERACTIONS IN A BIOTIC COMMUNITY Interactions in a Biotic community can broadly be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both. To understand them in a better way, let s assign a + sign for beneficial interaction, - sign for detrimental and 0 for neutral interaction and then try to look at all the possible outcomes of interspecific interactions. Accordingly, we shall observe that these interactions may manifest themselves in some of the following forms such as Mutualism, Commensalism, Parasitism, Predation, Competition and Amensalism etc. Lets discuss each of these interactions and seek to know how they actually operate in Nature . ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 9

Abhipedia IAS 1. 1.Mutualism: This interaction confers benefits on both the interacting species. Lichens represent an intimate mutualistic relationship between a fungus and photosynthesizing algae or cyanbacteria. Similarly, the mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy-yielding carbohydrates. The most spectacular and evolutionarily fascinating examples of mutualism are found in plant-animal relationships. Plants need the help of animals for pollinating their flowers and dispersing their seeds. Animals obviously have to be paid fees or so called allowance for the services that plants expect from them i.e. dispersal of its pollen grains. Plants offer rewards or fees in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersers.

Abhipedia IAS 2. Commensalism: This is an interaction in which one species benefits and the other is neither harmed nor benefited. Say for example, an orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale, benefit while neither the mango tree nor the whale derives any apparent benefit from the growth of such second species. The cattle egret and grazing cattle browsing in close association, a sight we are most likely to catch if we were to live in a farmed rural area, is a classic example of commensalism. The egrets always forage close to where the cattle are grazing because the cattle, as they move, stir up and flush out from the vegetation insects that otherwise might be difficult for the egrets to find and catch. Another common example is Clown fish and Sea Anemone. ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 11

Abhipedia IAS 3. Predation: Besides acting as conduits for energy transfer across trophic levels, predators ecologically play other important roles as well. They keep prey populations under control. But for predators, prey species could achieve very high population densities and cause ecosystem instability. When certain exotic species are introduced into a geographical area, they become invasive and start spreading fast because the invaded land does not have its natural predators. The prickly pear cactus introduced into Australia in the early 1920s caused havoc by spreading rapidly into millions of hectares of rangeland. Finally, the invasive cactus was brought under control only after a cactus- feeding predator (a moth) from its natural habitat was introduced into the country. Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population.

Abhipedia IAS 4. Competition: It is generally believed that competition occurs when closely related species compete for the same resources that are limiting, but this is not entirely true. Firstly, totally unrelated species could also compete for the same resources. For instance, in some shallow South American lakes visiting flamingoes and resident fishes compete for their common food, the zooplankton in the lake. Secondly, resources need not be limiting for competition to occur; in interference competition, the feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of the other species, even if resources (food and space) are abundant. ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 13

Abhipedia IAS 5. Parasitism: It is an interaction between two species what we call as HOST and PARASITE. To survive, the parasite develops certain adaptations such as: the loss of unnecessary sense organs, presence of adhesive organs or suckers to cling on to the host, loss of digestive system and high reproductive capacity. 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, human liver fluke (a trematode parasite) depends on two intermediate hosts (a snail and a fish) to complete its life cycle. The malarial parasite called as plasmodium, on the other hand, needs a vector (female Anopheles mosquito) to spread to other hosts.

Abhipedia IAS Majority of the parasites harm the host; they may reduce the survival, growth and reproduction of the host and reduce its population density. They might render the host more vulnerable to predation by making it physically weak. Ecologically speaking, the parasites can be of two types called as Ectoparasites and Endoparasites. Parasites that feed on the external surface of the host organism are called ectoparasites. The most familiar example of this group is the lice on humans and ticks on dogs. The female mosquito is not considered a parasite, although it needs our blood for reproduction because, it does not live in permanent association with the human host all the time which is an essential criterion for being a parasite. ABHIMANU IAS : COMPLETE GENERAL STUDIES PRE CUM MAINS COURSE CALL 7347432666, MAIL AT INFO@ ABHIMANU.COM.. 15

Abhipedia IAS In contrast, endoparasites are those that live inside the host body at different sites (liver, kidney, lungs, red blood cells, etc.). Brood Parasitism: What is it ? In some birds, a very fascinating example of parasitism can be seen what we call as brood Parasitism. Here, the parasitic bird lays its eggs in the nest of its host and lets the host incubate them. In nature, it is seen live in case of cuckoo laying her eggs in Crow s nest. During the course of evolution, the eggs of the parasitic bird have evolved to resemble the host s egg in size and color to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest. This can be easily observed in nature by watching the movements of the cuckoo (koel) and the crow in our neighborhood park especially during breeding season .