Community ecology
Community: The sum of populations of different species
within a given area.
An assemblage of plants, animals and Micro-organisms
inhabiting a given area.
Diverse Organisms live together in an orderly manner with
a definite trophic organization.
Each community has its special limit. Sometimes the
boundary between two communities may be very sharp or
gradual.
Community ecology or Synecology is
the study of the interactions between
species in communities on many spatial
and temporal scales, including the
distribution, structure, abundance,
demography, and interactions between
coexisting populations.
Study of the organization and functioning
of communities, which are assemblages of interacting
populations of the species living within a particular
area or habitat.
As populations of species interact with one another,
they form biological communities.
Structures arise within communities as species
interact among themselves
Food chains, food webs, guilds, and other interactive
webs are created.
These relationships change over evolutionary time as
species reciprocally adapt to one another through the
process of co-evolution
Levels of Organisation
Populations Interact and evolve
Sambhar
Trees
Bison
White Tiger
Community ecology seeks to explain the underlying
mechanisms (Process) that create, maintain, and determine the
fate of biological communities (Pattern).
P P
p p
p
Community attributes
Each biotic community exhibits a number of
characteristics, such as
Diversity / Richness Abundance
Dominance
Composition and
Stratification.
1. Species diversity: the variety of species in a
given area, region or a particular ecosystem & has
two components namely Species richness and
Species evenness
Within these species diversities,
Few species – Dominant Sp – Determines energy flow in
each trophic
Many species in small numbers – Determines Species Diversity
Low in managed environments
Coral reefs and rain forests have high species richness.
Shannon Weaver Index and Simpson’s Index – Measure of
Species diversity of a community.
Factors effect Species diversity
1. Temp, Light, Moisture, vegetation etc., in
terrestrial communities
2. Depth, pH, Current, salinity, Temp, Light
availability, Pollution levels etc., in aquatic
communities.
Species richness (# of species within community)
Species richness is the number of different species present in
a given area, region or in a particular ecosystem
Relative abundance (% each species
contributes to the total number of
individuals)
Shannon Weiner Index
https://www.youtube.com/watch?v=esBAg3Hu4WE
Simpson Diversity Index
2. Stratification
Vertical Stratification
Horizontal Stratification
Effects that cause Stratification –
Biotic - abiotic interference,
Tolerance,
adaptation,
competition, etc..
Zonation : Vertical Terrestrial Plant Community
Physical structure of
Biotic Community
Zonation :Horizontal Sea Shore Communities
Horizontal-zonation-ocean-stratification-benthic-
population
3. Dominants
Those organisms, which exert a major role in
having controlling influence on the
community, are called ecological dominants.
Major controlling influence of one species
upon all other species or the entire community
by virtue of their number, size, productivity
or related activities at the level of population
or community.
Dominants Species able to adapt and sustain
better compared to the other species
Keystone Species
Keystone species, have a disproportionately large effect on
the communities in which they occur. They help to maintain
local diversity within a community either by controlling
populations of species that would otherwise dominate the
community or by providing critical resources for a wide range
of species.
Keystone Species
In any community, the “keystone” is considered one of
the most vital parts. In any type of ecosystem,
a keystone species is an organism that helps hold the
system together.
There are three types of keystone species cited by many
scientists: Predators
Ecosystem engineers and
Mutualists.
Tiger / Leopard
Elephant pushing over larger trees allowing grasses to grow, which
benefits smaller herbivores. Also it breaks the canopy – allow sunlight to
reach the ground thereby allow the ground vegetation to grow.
Ficus Tree
https://www.youtube.com/watch?v=8fpKDtLjvaI
Bees and Flowers
Pisaster ochraceus - sea stars
Beaver Rat
https://www.youtube.com/watch?v=Dd-Bslj_bOI
Mangroves
Some more Key stone species
https://www.youtube.com/watch?v=JGcIp4YEKrc
Guilds and Interaction webs
Guilds often are composed of groups of closely related
species that all arose from a common ancestor.
They exploit resources in similar ways as a result of
their shared ancestry.
Exploit the same kinds of resources in similar ways
Often become competitors when resources are scarce
Example : Different insect species that collect nectar
Ecological Niche
There are two types of Niche
Fundamental niche – The maximum niche that the
species could occupy in the absence of competition from
other species
Realised niche – Is the part of the fundamental niche
which a species is able to occupy in face of competition
Eg: Tigers and Leopard
https://youtu.be/-6COob_bymw
Multidimensional Hypervolume Niche
Ecological Niche
Spatial niche – Eg: Tigers and Leopard
Trophic niche – Eg: Finches (birds)
– some are frugivorous
– some are insectivorous
Antibiosis
Proto-
Amensalism cooperation
• Species diverge from one another through competition,
with the result that they fill different niches within the
community.
The Effects of Competition…
When the species with large overlapping niches are
allowed to compete, their niches may focus on a
different part of the resource spectrum like the
North American Warbler Species.
The great differences in
bill size and shape that
some of Darwin’s finches
in the Galapagos have
evolved have resulted from
competition.
Resource partitioning – adapt to reduce competition
(Hawks & owls)
Co-evolution of Ficus – Ficus Wasp
https://www.youtube.com/watch?v=8fpKDtLjvaI
https://www.youtube.com/watch?v=LrmAbnlnqqo
These ocellaris clownfish are hiding in an anemone. Clownfish and
anemones live together in a mutualistic symbiotic relationship.
SIDEROXYLON GRANDIFLORUM - CALVARIA MAJOR
For a long time the tree was considered dying out. It did not reproduce
for 300 years! At the same time, the tree produced beautiful seeds, but
they did not germinate! What happened? Why was everything okay
before, but now not? Because of what the seeds did not germinate?
(Hint: The soil has nothing to do with it but with the Bird)
https://www.youtube.com/watch?v=FspqW7u0BRk
In Africa’s tropical forests Omphalocarpum
elatum produces fruits that can be as much as two
kilos in weight. These large fruits are sought after by
the forest elephants, and it is only the elephants that
can break through the hard shell.
https://www.bbc.co.uk/programmes/p006m9lr
Commensalism, which literally means "to eat at the same table" is one
form of symbiosis, a relationship between two organisms of different species.
In a commensal relationship, one organism benefits while the other is generally
unaffected.
Cattle Egrets
These birds live near cattle because when the cattle graze, their movements
stir up insects. Cattle egrets simply scoop up the insects disturbed by the
passage of the larger animal. The birds get a meal and the cattle are
unbothered, making for an example of commensalism in action
Proto-cooperation
Inter - species Interaction
Predation (+/-) One species (predator/hunter) lives off of another
species (prey/hunted)
Symbiosis : Mutualism , Commensalism & Parasitism
Parasitism (+/-) One species (parasite) lives on another species
(host)
Commensalism (+/0) One species benefits, but the other is not
harmed (Cattle & Egret)
Amensalism (-/0) One species affected One not benefitted
(Penicillium fungus – Bacteria)
Mutualism (+/+)Two species live together to benefit both (Clown
Fish – Sea anemone) (Obligatory in nature)
Proto cooperation = (+/+) But no Obligation (Crab - Sea
anemone)
Antibiosis (+/-) One species benefits, but the other is harmed by
secretion of Chemicals
Plant – Animal Interactions ina
Biotic Community
• Plant/herbivore relationship
• Plants and their pollinators
• Plants and their dispersers
• Mutualism – Dodo tree
• Antagonism – grazing, parasitism
• Commensalism
https://www.researchgate.net/publication/259438997_Plant-
animal_interactions_an_overview
Fungal – Plant Association
Mycorrhiza
Ecological succession is a series of progressive changes in the species
that make up a community over time.
What really happens in Succesion:
Afforestation in Rajasthan Deserts :
Species from Genera like Acacia and Prosopis
were planted by the Britishers in desert areas of
Rajasthan for Fire wood.
These species could survive on little water, were
good for nitrogen fixation and stabilised the
sand dunes in the desert.
Subsequently the soil was able to support other
plant species in the desert - a place where
afforestation usually is an arduous task.
Causes
Initial Causes : Climatic or Biotic
Continuing Causes : Activity of the Organisms induced
in the place
Stabilising Causes : Climate of the Area Predominant
factor
Gradual Early
Increase in Dominance by
Organic Heterotrophs
Matter such as
Bacteria, Fungi
etc.
Gradual
Decline in
energy content
Bases on moisture condition:
• Xerarch Succession: Succession initiated in
extremely dry situation, such as bare rock,
windblown sand etc., and establishment of a stable
community.
• Hydrarch Succession: Succession involves
replacement of more hydrophytic communities by less
hydrophytic and stabilization of a hydric habitat.
• Mesarch Succession: Conditions In-between..
Xerarch Succesion
Pioneer:
A Species that invades a bare
area such as a newly exposed soil
or rock surface.
Sere:
• Plant communities involved in succession.
• A number of transitional communities that
come after the pioneers and replace each
other.
Climax Community:
• That comes in the last and forms the stabilized
vegetation in the area.
• Disclimax / Sub-climax
Stages in Succession
Stages in Succession:
• NUDATION Exposure of a new substrate.
• INVASION :
Migration: Arrival of disseminates
(Spores, Seeds, Etc.,)
Excesis: Plants gets Established
– Germinations
– Establishment
– Growth
– Reproduction
Aggregation: Species Grouping.
• Competition: Intraspecific / Interspecific
• Reaction: Because of interaction and
Effects produced by one or group of
organism on Environment.
• Final Stabilization:
• Kinds of Succession:
Progressive: Species enrichment
associated with increased structure
complexity.
Regressive: Reversion of some
earlier stages of succession consequent to
introduction of an adverse factor.
Climax:
• A Succession ends with a community in
which the species stabilizer.
• Culminating stage in Plant / Community
Succession for a given environment the
vegetation being conceived as having
reached a highly stable condition.
Theories of Climax:
• Mono Climax Theory – Clement Proposes Climate as the
chief factor determining the climax species
• Poly Climax Theory – Tansley Proposes that not only climate,
host of other environmental factors also determine the climax
species – Edaphic climax, Biotic climax, Anthropogenic,
Grazing, Zootic, Topographic & Fire Climaxes
Uses of Succession:
• Classification of Forests
• Species Choice
• Evaluation of Sites for ecological restoration
Ecotone, a transitional area of vegetation between two
different biological communities
Steep Environmental gradient
Has some characteristics of each bordering biological
communities
An ecotone may exist along a broad belt or in a small
pocket, such as a forest clearing, where two local
communities blend together.
The influence of the two bordering communities on each
other is known as the edge effect.
An ecotonal area often has a higher density of
organisms of one species and a greater number of
species than are found in either flanking community.
Paleoecology
The ecology of the past, is the study and
understanding of relationships between
organisms and their environment in the past.
Paleoecologists study the physical structure and
biological functions of organisms, their
interactions with each other, and their role in
ancient ecosystems.
The goals of paleoecology are to understand the
details of ancient environments and the
functioning of ancient ecosystems and their
evolution.
• The primary database for paleoecological
studies is the fossil record. For example, by
studying fossils and comparing them with similar
living organisms.
• Paleoecologists attempt to understand how the
fossil organism lived and its ecological duties.
• Uses geological and biological evidence from
fossil deposits to investigate the past
occurrence, distribution, and abundance of
different ecological units (species, populations,
and communities) on a variety of timescales.
