COMPILED AND CIRCULATED BY DR. PRITHWI GHOSH, ASSISTANT PROFESSOR, DEPARTMENT OF BOTANY, NARAJOLE RAJ COLLEGE
Plant Communities
[Habitat and niche, Ecotone and Edge effect]
An ecotone is an area that acts as a boundary or a transition between two ecosystems. A
common example could be an area of marshland between a river and its riverbank. Ecotones
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 species 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
forests (between terrestrial and
marine ecosystems), grasslands
(between desert and forest), 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.
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
• 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 community structures that occur at the
boundary of two habitats. 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).
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
• 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, sunlight, 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 ecological niche
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 competition. If neither evolves to reduce
competition, then the species that can more efficiently exploit the resource will win out, and
the other species will eventually become extinct.
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
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 nature, 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
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
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 microorganisms, 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.]
BOTANY: SEM-IV, PAPER-C9T: PLANT ECOLOGY & PHYTOGEOGRAPHY, UNIT 7: PLANT COMMUNITIES