Ecotone, edge effect, ecological niches etc.

1. Community ecology
Definition:
A community is a set of organisms coexisting within a defined area.
• A group of population living in a unit area
• Community ecology is the study of co-existing, interdependent
populations
Community ecology is the study of the interactions between these
organisms, and the interactions between the organisms and their
environment.
Types of Communities:
Kendeigh (1974) divided the biotic com-munity into two types
 Major communities
 Minor communities
Major community
It is a large, self-sustaining and independent unit
Eg:- coral reefs, rocky community, mangroves etc.
Minor community
It is smaller, not self-sustaining and dependent on other communities for
growth and survival but it is found in major community
Example - Barnacles, Oysters, Algae, Polychaetes present rocky
shores.
Characteristics of a community:

2. The characteristics by which a community is designated are as follows
1) Species Diversity
A biotic community has producer, consumer & decomposer. Within these
species diversities, some populations exert more influence than others in
the community because the share a higher % of energy flow.
2) Growth & Structure
Community is usually described in term of growth forms. The growth form
is the general appearance of plant. These growth forms are directly
influenced by environmental factors.
3) Dominance
In each community, one or a few species dominate either in numbers or in
physical characteristics or both over the other species.
The dominant species are called ECOLOGICAL DOMINANTS.
4) Successions
Successionis very important in development of community. Community
develops as a result of directional change in it with time.
5) Trophic levels
There are 3 broad trophic levels in a community which are Producers,
Consumers & Decomposers. The food produced by the green plants is
consumed directly or indirectly by all kinds of animals. So these are known
as Consumers.
The dead bodies & excreta of both producers & consumers are decomposed
by microbes into simple substances, these are called the Decomposers of
the community

3.  Stratification in the field of ecology refers to the vertical layering of
a habitat
 The arrangement of vegetation in layers.
 It classifies the layers of vegetation largely according to the different
heights to which their plants grow.
 The individual layers are occupied by different animal and
plant communities (stratozones).
Types of Stratification:
1. Vertical stratification
2. Horizontal stratification
Vertical stratification:
 It refers to the vertical distribution of organisms in a community.
 Vertical stratification is found in forestcommunity, grassland
community and aquatic communities.
Eg: forest community
A forest is formed of five layers.

4. Sunlight is the main cause behind the development of vertical stratification.
STRATIFICATION in FOREST COMMUNITY- A forest community shows
5 vertical strata:
1) Subterranean Strata- Basal portion, covered by litter & debris of plants as
well as animals.
2) Forest Floor- Secondlayer, abundance of litter. This region is the zone of
decomposition.
3) Stratum of Herbaceous Vegetation- Thirdlayer, formed by herbaceous
plant like grasses, dicotyledonous annuals etc.
4) Stratum of Shrubs- Locatedbelow the crown layer & above the
herbaceous layer, represented by shrubby life form.
5) Stratum of Tree- Topmostlayer, also called CROWN LAYER which
represents highest limit of plant community in given region.

5. Horizontal stratification:
It refers to the distribution of individuals on a horizontal plane in the
community. In a terrestrial community, the individuals may be distributed
on the floor in three ways, namely uniform, clumped and random.
The spatial distribution of individuals within the population
Three types:
 Clumped Dispersion
 Even Dispersion
 Random Dispersion
Clumped Dispersion
 Individuals are clustered together
Occurs:
 When resources (food, water, living spaces) are clumped together
 Species have a certain social behavior
 For example: herding animals, flocks of birds, schools of fish,
hives of bees
Even Dispersion (a.k.aUniform Dispersion)
Individuals are separated by a fairly even distance.
Occurs:
 As a result of social interaction
 Individuals trying to get as far away from each other as
possible.
 Limited resources, competition, nesting

6. Random Dispersion
Location of one individual is independent of the location of the other
individuals
Examples:
 Seed dispersal by the wind or animals
ECOLOGICAL DOMINANCE
• The ecological dominance is also known as the dominant species
• It refers to the most of population in a climax community
• Ecological dominance is the degree to which a species is more
numerous than its competitors in an ecological community or makes
up more of the biomass
• Most ecological communities are defined by their dominant species
• In tropical coastal waters the dominant corals

7. • In temperate bogs, the dominant vegetation is usually species
of Sphagnum moss.
• On earth, a large amount of its land ecosystems are dominated
by human beings, making human beings the ecologically dominant
species over much of the planet.
• Tidal swamps in the tropics are usually dominated by species of
mangrove (Rhizophoraceae)
• Some sea floor communities are dominated by brittle stars.
• Exposed rocky shorelines are dominated by sessile organisms such
as barnacles and limpets.
Community dominance
• A community has many species, of which one or few species play
dominant role in the community by virtue of their number, size and
activities such species are called ‘Community dominance’
• The removal of community dominant from the community affects
the community drastically
• Species structurein most communities is either abundant or rare
• Few spices that are abundant
• Large number species that are rare
• The abundant species are called dominants. Eg. The mussel bed in
the rocky shore –Mytilus sp
Ecotone and edge effect
• Ecotone is the intermediate zone lying between two adjacent
communities

8. Eg. An estuary is an ecotone lying between river and sea
Characteristics of ecotone
• The ecotone prevails environmental conditions intermediate to both
two adjacent communities
• The ecotone offers an abundance of food and shelter
• It contain organisms of both community
• As a rule ecotone contains more species often denser population than
either of the neighbouring communities. This is called edge effect
• The ecotone contain certain species which are completely restricted to
this region and they are called edge species
• The ecotone may be as broad as 100 km. or as narrow as 1 .0 km.
Ecological niche
• Niche refers to the functional status of an organism in its community
• According to Odum niche is the Professionof an organism in the
community
• Habitat - address and niche – Profession

9. • Niche includes what it eats, how it behaves, how it responds to the
environment and interactions with other organisms in the
community
Ecological niches may be
• Broad niche
• Narrow niche
• Narrow niches - the role or function in the community or ecosystem
has more finely subdivided and the species is specialized
• Specialized species are also called specialists
• Eg:- muddy, sandy , rocky etc.
• Broad niches - the species functions in the community is more of
generalized
• They are either specialists or generalists with referenceto the niche -
Marine or fresh water, estuarine organisms etc.
Ecological succession

10. • The process of development of new communities is called ecological
succession
• “An orderly and progressive replacement of one community by
another till the development of a stable community in that area”
(Smith, 1965).
Characteristics of succession
• The successionis caused due to the modification of the habitat
• The kinds of programs changes continuously with succession
• The diversity of species increases. biomass can also increases
• The first stage of community is ‘pioneer community’ The final stage
of community called ‘climax community’
Types of succession
• Primary succession – Bacteria, Lichens – first community (pioneer) on
rocks – biofilm
• Secondary succession-Attachedof spats of barnacles, oyster,
polychaetes etc. on pioneer communities
• Autotrophic succession - Dominance of algae.
• Heterotrophic succession– Dominance of heterotrophs
Climax community

11. • The terminal and persistent community in an ecosystemis called
climax community.
Animal are broadly grouped
into
• R- selected species
• K-selected species
R-Strategists
Think “R” for “reproduction”
 Population usually NOT
near carrying capacity
 J-curve growth (high growth
rate)
 Exponential Growth
 Highly affected by abiotic
factors like weather
 Small body size and short
life span
 Have many offspring in a
short time
K-Strategists
Think “K” for “carrying capacity”
 Population lives near its carrying capacity
 S-Curve Growth
 Logistic Growth

12.  Highly affected by biotic factors like competition
 Usually large body size
 Have few offspring, but live a long time
Ecotone:
 An ecotone is a zoneof junction or atransition areabetweentwo biomes
[diverse ecosystems]. It is where two communities meet and integrate.
 For e.g. the mangrove forestsrepresentan ecotone between marine and
terrestrial ecosystem. Other examples are grassland (betweenforestand
desert), estuary (between fresh water and salt water) and river bank or
marsh land (between dry and wet).

Characteristics of Ecotone
 It may be narrow(between grasslandand forest)or wide (between forest
and desert).

13.  As it is a zone of transition, it has conditions intermediate to the adjacent
ecosystems. Hence it is a zone of tension.
 Usually, the number and the population density of the species of an
outgoing community decreases as we move away from community or
ecosystem.
 A well-developed ecotones contain some organisms which are entirely
different from that of the adjoining communities.
Edge Effect – Edge Species
 In ecology, edge effects refer to the changes in population or
community structures that occur at the boundary of two habitats
(ecotone).
 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 edgeeffect is especially applicable to birds.
For example the density of birds is greater in the mixed habitat of the
ecotone between the forest and the desert.
Ecological Niche

14.  Niche refers to the unique functional role and position of a speciesin
its habitat or ecosystem.
 In nature, many species occupy the same habitat but they perform
different functions.
 The functional characteristics of a species in its habitat is referredto as
“niche” in that common habitat.
 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, a large number of differentspecies of insects may be pests
of the same plant but they can co-exist as they feed on different parts of
the same plant.

15.  A species’ niche includes all of its interactions with the biotic and abiotic
factors of its environment [habitat niche – where it lives, food niche –
what is eats or decomposes & what species it competes with,
reproductive niche – how and when it reproduces, physical & chemical
niche – temperature, land shape, land slope, humidity & other
requirement].
 An ecological niche describes how an organism or population responds
to the distribution of resources and competitors (for example, by
growing when resources are abundant, and when predators, parasites
and pathogens are scarce) and how it in turn alters those same factors
(for example, limiting access to resources by other organisms, acting as
a food source for predators and a consumer of prey).
 Niche plays an important role in conservation of organisms.If we have
to conservespecies in its native habitat we should have knowledge about
the niche requirements of the species and should ensure that all
requirements of its niche are fulfilled.