COMPILED AND CIRCULATED BY DR. PRITHWI GHOSH, ASSISTANT PROFESSOR, DEPARTMENT OF BOTANY, NARAJOLE RAJ COLLEGE

Plant Communities

[ and niche, and Edge effect]

An ecotone is an area that acts as a boundary or a transition between two . A

common example could be an area of marshland between a river and its riverbank.

are of great environmental importance. Because the area is a transition between two

ecosystems or biomes, it is natural that it contains a large variety of of fauna and flora

as the area is influenced by both

the bordering ecosystems.

Examples of ecotones include

marshlands (between dry and

wet ecosystems), mangrove

(between terrestrial and

marine ecosystems), grasslands

(between desert and ), and estuaries (between saltwater and freshwater). Mountain

ranges can also create ecotones due to the changes in the climatic conditions on the slopes.

Characteristics of Ecotones

• It may be wide or narrow.

• It is a zone of tension (as it has conditions intermediate to the bordering ecosystems).

• It could contain species that are entirely different from those found in the bordering

systems.

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• Ecotones can be natural or man-made. For example, the ecotone between an

agricultural field and a forest is a man-made one.

Importance of Ecotone

1. They have a greater variety of organisms.

2. They also offer a good nesting place for animals coming in search of a nesting place

or food.

3. They serve as a bridge of gene flow from one population to another because of the

larger genetic diversity present.

4. They can act as buffer zones offering protection to the bordering ecosystems from

possible damage. For example, a wetland can absorb pollutants and prevent them

from seeping into the river.

5. Ecotones are also a sensitive indicator of global climate change. A shifting of

boundaries between ecosystems is thought to be due to climate change. So, scientists

and environmentalists are studying ecotones with greater interest now.

Edge Effect

Edge effects refer to the changes in population or structures that occur at the

boundary of two . Generally, there is a greater number of species found in these

regions (ecotones) and this is called the edge effect. The species found here are called edge

species.

• Edge effect refers to the changes in population or community structures that occur at

the boundary of two habitats (ecotone).

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• Sometimes the number of species and the population density of some of the species

in the ecotone is much greater than either community. This is called edge effect.

• The organisms which occur primarily or most abundantly in this zone are known as

edge species.

• In the terrestrial ecosystems edge effect is especially applicable to birds.

• For example, the density of birds is greater in the ecotone between the forest and the

desert.

Ecological Niche

Niche is the functional role and position of a species in its environment that describes

how the species responds to the distribution of resources and competitors or

predators.

Ecological niches have specific characteristics, such as availability of nutrients, temperature,

terrain, , and predators, which dictate how, and how well, a species survives and

reproduces. A species carves out a niche for itself in a habitat by being able to adapt and

diverge from other species. Modern-day ecologists study ecological niches in terms of the

impact the species has on its environment, as well as the species’ requirements. According

to the competitive exclusion principle, two species cannot occupy the same

in a habitat if they are competing for the same resources. When species compete in a

niche, natural selection will first move to lessen the dependence of the species on the shared

resources. If one species is successful, it reduces the . If neither evolves to reduce

competition, then the species that can more efficiently exploit the will win out, and

the other species will eventually become extinct.

BOTANY: SEM-IV, PAPER-C9T: PLANT ECOLOGY & PHYTOGEOGRAPHY, UNIT 7: PLANT COMMUNITIES

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Difference between niche and habitat

• The habitat of a species is like its ‘address’ (i.e., where it lives) whereas niche can be

thought of as its “profession” (i.e., activities and responses specific to the species).

• A niche is unique for a species while many species share the habitat.

• No two species in a habitat can have the same niche. This is because of the competition

with one another until one is displaced.

• For example, many different species of insects may be pests of the same plant, but

they can co-exist as they feed on different parts of the same plant.

Fundamental and realized niches:

In 1958, Hutchinson introduced the

terms fundamental niche and

realized niche. Fundamental niche

is the niche that an organism would

occupy in the absence of

competitors and predators. When

the fundamental niches of two species overlap, then the two species are said to be competing

with one another.

However, in , two species do not overlap or compete for food, even if they eat the items

of the same size, as they can look for them in different places. Most well-integrated

communities like coral reef, climax forest etc. are made up of species with non-overlapping

niches. Realized niche is referred to as the role an organism actually plays in the community.

Hutchinson viewed that the outcome of inter-specific competition would lead either to

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extinction or the development of differences allowing coexistence. In nature, the realized

niche of an organism is smaller than its fundamental niche

Advantages of Ecological Niche:

1. Animals can escape competition by occupying different ecological niches.

2. The ecological niche occupied by a species is favorable to it as it furnishes a suitable sub-

stratum and microclimate.

3. Segregation of organisms into niches avoids confusion of activities in the community and

gives a more orderly and efficient life pattern for each species.

4. Segregation of different species in a particular niche results in full exploitation of all

available resources.

Competitive exclusion principle

The competitive exclusion principle tells us that two species can't have exactly the same

niche in a habitat and stably coexist. That's because species with identical niches also have

identical needs, which means they would compete for precisely the same resources.

A famous example of the competitive exclusion principle is shown in the figure below, which

features two types of single-celled , Paramecium aurelia and Paramecium

caudatum. When grown individually in the lab, both species thrive. But when they are grown

in the same test tube (habitat) with a fixed amount of nutrients, both grow more poorly

BOTANY: SEM-IV, PAPER-C9T: PLANT ECOLOGY & PHYTOGEOGRAPHY, UNIT 7: PLANT COMMUNITIES

COMPILED AND CIRCULATED BY DR. PRITHWI GHOSH, ASSISTANT PROFESSOR, DEPARTMENT OF BOTANY, NARAJOLE RAJ COLLEGE

and P. aurelia eventually outcompetes P. caudatum for food, leading to P. caudatum's

extinction.

Image modified from

"Community ecology: Figure 7,"

by OpenStax College, Concepts

of Biology, CC BY 4.0(Opens in a

new window).

References

• www.biologydiscussion.com • www.bioninja.com • www.wikipidea.com • www.slidepalyer.com

[The information, including the figures, will be used solely for academic purpose.]

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