Concept of Biotic
Community
Biotic
Community
• also known as biota or ’biocoenosis’
• is the group of organisms that live together and
interact with each other within an environment or
habitat
• Together, the biotic community and the physical
landscape or abiotic factors make up an ecosystem.
Types of Community
o
Minor
communities
Major
communities
o
Are those communities more or
less dependent on neighboring
communities for energy
They are secondary
aggregations within a major
community
o Are those communities of
sufficient size and completeness
of organization
o They are relatively independent of
resources from adjacent
communities
o They receive only solar energy
from the sun
Concept of Biotic Community
Community concept is important in ecological
thought and in ecological practice because..
 it emphasizes the fact that diverse organism
live together in an orderly manner
 “as the community goes, so goes the organism”
features…
 A community is an aggregate of organism of
various sizes, which form a distinct features
cont…
• The
size
of
community
unit
maybe large (forest
community) or small
(community
of
invertebrates)
• Different community
occurs in different
habitat
• The composition and character of a community is
an indicator of the type of environment that is
present
cont…
• The structure of a community is dependent on:
a) the number of species
b) the relative number of individuals in each
species
• Communities are constantly changing. The
replacement of one community by another is
called community succession. The final stage in
community succession is a climax community
• Species diversity indices give quantitative
expression of community structure
IntraCommunity
Classification and
Concept of Ecological
Dominance
Ecological dominance
• is the degree to which a taxon 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.
• few species or species groups exert the major
controlling influence by virtue of their numbers,
size, production or other activities.
• Major communities largely control the energy
flow and strongly affect the environment of all
other species
cont…
• Natural communities may have an even larger number
of species. Even so, a relatively few species often
control the community and are said to be dominant.
• Removal of the dominant would result in important
changes not only in the biotic community but also in
the physical environment.
• Removal of a non-dominant species would produce
much less change
• Generally, dominants are those species in trophic
groups which have the larges productivity or biomass
Intracommunity Classification
therefore…
 goes beyond taxonomic listing and attempts to evaluate the
actual importance of organisms in the community.
bluegrass
white clover
oak trees
beef cattle
dairy cattle
chickens
turkeys
sheep
horses
48 acres
2 acres
2 individuals
2 individuals
48 individuals
6 individuals
2 individuals
1 individual
1 individual
Species Diversity in
Communities
Species Diversity in Communities
• Species diversity is the key features of biological
communities
• Species diversity affects the stability and
productivity of communities
• Species diversity declines as latitude increases
• small percent of individuals are
abundant while large percent are rare
usually
cont…
• Few common species or dominants largely
account for the energy flow in each tropic group
• It is the large number of rare species that largely
determine the species diversity of trophic groups
and whole communities
• Species diversity tends to be low in physical
controlled ecosystem while high in biologically
controlled ecosystem
• Diversity is positively correlated with stability
Pattern in
Communities
Pattern in Communities
1)
2)
3)
4)
5)
6)
7)
8)
Stratification pattern (vertical layering)
Zonation pattern (horizontal segregation)
Activity pattern (periodicity)
Food web pattern (network organization in food
chain)
Reproductive pattern (parent-offspring
association, plant clones, etc.)
Social pattern (flocks and herds)
Coactive pattern (resulting from competition,
antibiosis, mutualism, etc.)
Stochastic patterns (resulting from random
forces)
Example of stratification
Example of zonation
Activity pattern
The rhythmic changes occur in the activities of
organisms.
• Seasonal periodicity- temperate, rainfall and
photoperiod determine the reproductive cycle
of its inhabitants
• Dial periodicity- animals of terrestrial
community active during the day and inactive
during the night
Example of Food web pattern
Reproductive pattern
Asexual reproduction –relies entirely on mitosis
1. Fission 2. budding 3. fragmentation
Sexual reproduction
1. Parthenogenesis – eggs develop w/out being
fertilized. Ex: bees, wasps, etc.
2. Hermaphroditism – Some fertilize themselves
but most fertilize mutually where each donates
and receives sperms
3. Sequential hermaphroditism – an organism
changes its gender throughout its lifetime
Ecotones and
Concept of Edge
effect
Ecotones and Edge effect
• Ecotones, also called transition
zone
• was coined from a combination
of eco(logy) plus -tone, from the
Greek tonos or tension (a place
where ecologies are in tension).
• The zone where two or more
different communities meet and
integrate
• It is a junction zone or tension
belt but is narrower than the
adjoining community
cont…
• The zone maybe narrow
or wide, local (field and
forest)
or
regional
(forest and grassland)
• Ecotone contain both
communities
• Species in ecotone is
greater than in adjoining
communities
• It may also include a
number
of
highly
adaptable species that
tend to colonize such
areas
cont…
• the tendency of increased variety and density at the
community border and spend the greatest amount
of their time in junctions between communities is
known as edge effect.
• the ecotone between the field and the forest act as
a refuge for species formerly found in the ploughed
area
• Some species requires to be in ecotone as part of
their life cycle