UNIT 2

• Community ecology-Community structure

• Species interaction
• Biodiversity- types and uses
• Concept of Ecotone
• Methods of studying communities
 COMMUNITY ECOLOGY

• It is a study of the organization and functioning of communities which are

assemblages of interacting populations of the species living within a particular
area or habitat

• Community ecology represents the population of all species living and interacting
in an area at a particular time.
 STRUCTURE OF COMMUNITY

• Structure of community describes what creatures are present in a given

ecosystem, in what quantities, and how they interact.
• Many variables influence community structure, including abiotic influences,
species interactions, disturbance levels, and random events.
• Foundation species and keystone species, for example, play critical roles in
shaping the structure of their ecosystems.
 Structure of a Community

1. Community and Population

• A community refers to all the populations of various species that live in a particular area and
interact with one another.
• In contrast, a population is a group of individuals from the same species living in the same area
and interacting.
2. Biotic Components
• Communities consist of biotic components, meaning all living organisms in a particular area.
These organisms interact through processes such as competition, predation, and symbiosis.
Examples of communities:
• A coral reef teeming with fish, corals, and invertebrates.
• A stand of pine trees hosting birds, insects, and fungi.
• Organisms in aquatic environments like lakes, streams, or rivers.
3. Community Structure
The structure of a community is shaped by several factors and can be measured by:
• Species richness: The total number of different species present.
• Species diversity: A combination of species richness and evenness, which accounts for the
distribution of individuals across species.
Example: In a tropical rainforest, the structure may include hundreds of species coexisting, whereas
an Arctic tundra may have far fewer species but still form a well-defined community.
4. Influences on Community Structure
Several factors affect how communities are structured:
• Abiotic influences: Non-living environmental factors like temperature, water availability, and
soil type.
• Species interactions: Relationships like competition, predation, and mutualism.
• Disturbance levels: Events like fires, floods, and storms that can shape which species dominate.
• Random events: Unpredictable factors that may cause changes in community composition.
5. Foundation Species and Keystone Species
• Foundation species: Species that play a significant role in creating or maintaining a habitat, such
as corals in coral reefs or trees in forests.
• Keystone species: Species with a disproportionately large impact on the community relative to
their abundance, like sea otters in kelp forests or wolves in Yellowstone.
6. Variation in Community Types
• Communities vary in structure depending on geographic location and environmental conditions.
• Example: Tropical rainforests, known for high species richness, contrast with Arctic
communities, where few species are adapted to harsh conditions.
 CHARACTERISTICS OF A COMMUNITY

The characteristics of a community in ecology refer to the key aspects that define the organization,
composition, and interactions of species within an ecological community. Here are the main characteristics:
1. Species Diversity
• Species Richness: The number of different species present in the community.
• Species Evenness: The relative abundance of individuals across different species, contributing to the
balance within the community.
• Species Diversity: A combination of species richness and evenness, often measured using indices like the
Shannon-Wiener index.
2. Species Composition
• Refers to the identity of the species present in the community. It defines which species exist in a particular
area and their role in the ecosystem.
• Example: The species composition of a desert community includes cacti, reptiles, and certain bird species,
while a rainforest might have various tree species, insects, birds, and mammals.
3. Dominance
• Dominant species: Species that are most abundant or have the largest biomass and significantly
influence the environment and interactions within the community.
• Example: Oak trees in a forest can dominate in terms of biomass, providing habitat and resources
for many species.
4. Trophic Structure
• Describes the feeding relationships between species in the community and is typically represented
as food chains or food webs.
• It includes producers (plants), consumers (herbivores and carnivores), and decomposers (fungi,
bacteria).
• The trophic structure helps in understanding the energy flow and nutrient cycling within a
community.
5. Stability
• The ability of a community to maintain its structure and function over time, even in the face of
disturbances like natural disasters or human impacts.
• Resilience: The ability of a community to recover after disturbance.
• Resistance: The ability to remain unchanged when subjected to disturbance.
6. Stratification (Spatial Structure)
• Communities often have a vertical structure or stratification, especially in environments like
forests or aquatic systems. Different species occupy different layers, creating a multi-level
organization.
Example: In a forest, there are layers like the canopy, understory, shrub layer, and ground layer,
each supporting different species.
7. Succession The process by which community structure changes over time, especially after a
disturbance. There are two types:
o Primary Succession: Occurs in lifeless areas (e.g., volcanic islands).
o Secondary Succession: Occurs in areas where a community has been disturbed but soil and
life remain (e.g., after a forest fire).
8. Niche Structure
• The role of each species in the community, including how they use resources and interact with
others. Niches can be fundamental (potential role) or realized (actual role due to competition or
other limiting factors).
9. Zonation
• Communities are often structured into zones based on environmental gradients such as
temperature, moisture, or altitude.
• Example: Zonation can be observed in mountain ecosystems, where different species inhabit
different altitude zones, or in marine ecosystems, where species differ based on depth and
proximity to the shore.
10. Interactions Between Species
• Communities are shaped by species interactions such as:
o Competition: Species vie for the same resources (e.g., food, space).
o Predation: One species feeds on another.
o Mutualism: Species interact in ways that benefit both.
o Commensalism: One species benefits while the other is unaffected.
11. Keystone and Foundation Species
• Keystone species: Species with a disproportionately large impact on community structure and
function.
• Foundation species: Species that create or modify habitats and thereby influence the community’s
structure.
 TYPES OF ECOLOGICAL COMMUNITIES

Major Minor Natural Artificial Open Close

Communities in ecology are classified into different types based on their structure, scale, and environmental
conditions

1. Major (Climax) Communities

• Definition: These are relatively stable, self-sustaining communities that are the final stage of ecological
succession. They develop over time and remain in equilibrium with the local climate and environment.
• Example: A temperate deciduous forest is a major community that has developed after a long succession
process, consisting of large trees like oaks, maples, and a variety of animal species such as deer, birds, and
insects.
2. Minor (Subclimax) Communities
• Definition: These are communities that exist temporarily or are in an early stage of succession. They do
not represent the final stage of succession and may change due to disturbances or environmental shifts.
• Example: A grassland that forms after a fire or other disturbance and before the forest re-establishes itself
is a subclimax community.
3. Natural Communities
• Definition: Communities that have developed naturally through ecological processes, without
significant human intervention. They maintain themselves over long periods, shaped by the
natural environment.
• Example: A coral reef is a natural community that forms in shallow tropical oceans, consisting of
corals, fish, mollusks, and other marine organisms that interact and maintain a complex
ecosystem.
4. Artificial Communities
• Definition: Communities that are created or significantly influenced by human activity. These
communities are often less stable and may require human intervention to maintain.
• Example: A crop field is an artificial community where humans plant and manage specific species
(e.g., wheat, corn), along with associated organisms like insects, weeds, and soil microbes.
7. Open and Closed Communities
• Open Communities:
o Definition: Communities that have gradual boundaries and allow species to move in and
out. The transition between this community and others is not sharp.
o Example: A prairie transitioning into a forest is an open community, where grassland
species gradually give way to woodland species.
• Closed Communities:
o Definition: Communities that have well-defined boundaries and show sharp distinctions
from other communities.
o Example: An island ecosystem can be a closed community, with clearly defined
boundaries due to its isolation from other ecosystems.
 Elements of Communities

• Primary producers (autotrophs) plants and algae make their own

food through photosynthesis.
• Secondary consumers (herbivores)-Feed on primary Producers
• Tertiary Consumers ( Carnivores or Predators) Feed on herbivores
• Omnivores Feed on plants and Animals
• Its also includes the flow of energy through various trophic levels.
 SPECIES COMPOSITION
The collection of species present in a community. It refers to which species are found in a specific
area and how they interact with one another.

1. Native Species –are those species that typically live and thrive in particular ecosystem and have
been present there for a long period of time. Example Kangaroo, American bison
2. Non-Native species -are species which are either deliberately or accidentally introduced into an
ecosystem. Example Zebra Mussel, European Rabbit
3. Indicator species –are species which are particularly sensitive to environmental change and so
serve as signs of early warning of damage to a community. Example Mayfly Larvae, Lichens
4. Keystone species are the species that play a more important role in ecosystem than would be
suggested by their population. Example Sea otters, Beavers, Wolves, Elephants.
 SPECIES INTERACTIONS

Positive Negative

Competition (- / -)
•Definition: Competition occurs when two or more species vie for the same resources (such as food, space, or
light), which are limited in supply. In this interaction, both species are negatively affected because they have to
share resources.
•Types of Competition:
• Intraspecific Competition: Occurs between individuals of the same species.
• Interspecific Competition: Occurs between individuals of different species.
•Example:
• Plants Competing for Light: In a dense forest, trees and understory plants compete for sunlight. Taller
trees may overshadow smaller plants, limiting their access to light.
• Lion and Hyena: Lions and hyenas compete for the same prey, such as antelope, leading to intense
competition in African savannas.
•Outcomes:
• Competitive Exclusion Principle:
• Resource Partitioning
Predation (+ / -)
•Definition: Predation is an interaction where one species (the predator) hunts,
kills, and consumes another species (the prey). The predator benefits, while the
prey is harmed.
•Example:
• Lion and Zebra: Lions prey on zebras in the African savanna. The lion
benefits by gaining food, while the zebra population is reduced.
• Eagle and Fish: Eagles hunt fish by swooping down and capturing them
from lakes or rivers, benefitting the eagle while reducing the fish population.
•Adaptations:
• Predators: Adaptations include sharp teeth, claws, speed, camouflage, and
keen senses to locate and capture prey.
• Prey: Prey species may evolve defensive adaptations such as camouflage,
warning coloration, mimicry, or behaviors like fleeing or forming herds for
protection.
Parasitism (+ / -)
•Definition: Parasitism is an interaction in which one species (the parasite)
benefits by living in or on another species (the host), which is harmed but not
immediately killed. Parasites rely on their hosts for food and resources.
•Example:
• Tapeworm in Mammals: Tapeworms live in the intestines of mammals,
absorbing nutrients from the host's food. The tapeworm benefits, while
the host may suffer malnutrition.
• Ticks on Deer: Ticks feed on the blood of deer, gaining sustenance while
potentially transmitting diseases and causing harm to the host.
•Types of Parasites:
• Ectoparasites: Live on the outside of the host (e.g., fleas, ticks).
• Endoparasites: Live inside the host (e.g., tapeworms, heartworms).
Mutualism (+ / +)
•Definition: Mutualism is a type of interaction where both species
benefit from the relationship. Mutualistic interactions are often
crucial for the survival of the species involved.
•Example:
• Bees and Flowers: Bees gain nectar from flowers as food,
while they help pollinate the flowers, allowing them to
reproduce.
• Coral and Zooxanthellae: Corals form a mutualistic
relationship with algae (zooxanthellae) that live inside their
tissues. The algae provide the coral with food through
photosynthesis, and the coral provides the algae with
protection and access to sunlight.

•Types of Mutualism:
• Obligate Mutualism: The species involved are so dependent on each other that they cannot
survive without the mutualistic relationship (e.g., lichen, which is a combination of algae and
fungi).
• Facultative Mutualism: The species can survive independently, but their fitness is increased
when they engage in mutualistic interactions. Ants farmed aphids for honeydrops
Commensalism (+ / 0)
•Definition: Commensalism is an interaction where one species benefits while the other is neither
helped nor harmed. This relationship often involves one species using another as a platform or
habitat.
•Example:
• Barnacles on Whales: Barnacles attach themselves to the skin of whales, gaining a ride
through the ocean and access to food particles in the water. The whale is unaffected by the
barnacles' presence.
• Epiphytic Plants on Trees: Some plants, such as orchids, grow on the branches of trees,
gaining better access to sunlight. The tree is neither harmed nor benefited by this interaction.

Amensalism (- / 0)
•Definition: Amensalism is an interaction where one species is harmed while the other is
unaffected. This interaction is less common than others and usually involves a situation where one
species accidentally harms another.
•Example:
• Tree Shading Small Plants: Large trees may unintentionally block sunlight, causing harm to
small plants growing underneath, while the tree remains unaffected.
• Cattle Trampling Grass: As cattle move through a field, they may trample and destroy
plants without any direct benefit or harm to themselves.
The concept of ecotone refers to a transitional area where two distinct ecosystems or biological communities meet
and blend. This boundary region can occur naturally between ecosystems such as forests and grasslands, rivers
and oceans, or deserts and savannas. Ecotones exhibit characteristics of both adjacent ecosystems and often have
unique species and ecological conditions.

Key Features of Ecotones:

1.Transitional Nature:
1. An ecotone is a transition zone where species from the adjacent ecosystems interact. It represents a
gradual or sharp shift in environmental conditions like temperature, moisture, or light.
2. Increased Biodiversity:
Ecotones often support a higher diversity of species compared to the adjacent ecosystems.
This is because species from both ecosystems, along with species unique to the ecotone itself,
can coexist in the region.
3. Species Interaction and Adaptation:
1. Species living in ecotones may exhibit adaptations that allow them to survive in the
changing conditions of the boundary zone. These species may be better equipped to deal
with environmental variability.
2. Ecotones often have indicator species that are specially adapted to the conditions in the
transitional area.
4.Environmental Gradient:
1. Ecotones represent a gradient in environmental factors such as light, soil moisture, nutrient
availability, and other abiotic factors. This gradient influences which species are present
and how they interact.
5.Sensitive to Changes:
1. Ecotones are sensitive to environmental changes such as climate change, land-use changes,
and human activity. They can serve as early indicators of ecological shifts because of their
location at the intersection of different ecosystems.
 TYPES OF ECOTONES
1.Natural Ecotones:
1. These occur naturally between ecosystems. Examples include:
1. Forest-Grassland Ecotone: Where a forest gradually gives way to grassland.
2. Riverbank Ecotone: The transition from aquatic to terrestrial ecosystems along the edge
of a river.
3. Mangrove Ecotone: The zone where land meets the sea, often found in tropical coastal
areas.
2.Anthropogenic Ecotones:
1. These are human-created ecotones, often resulting from activities like deforestation,
agriculture, or urbanization. An example is the boundary between agricultural land and a
forest.
Examples of Ecotones:
•Forest to Grassland Transition: The area between a forest and a grassland supports species from
both environments. You may find both tree species and grassland species in this transitional zone.
•Estuaries: Where freshwater rivers meet the saltwater of the ocean. This ecotone supports unique
species adapted to the mix of salt and freshwater conditions.
•Mountain Ranges: As altitude increases, there is a transition from forests at lower elevations to
alpine meadows and eventually to rocky, barren land. Each zone has its own distinct communities,
with transitional zones in between.
Importance of Ecotones:
1.Biodiversity Hotspots:
1. Ecotones often act as hotspots for biodiversity, housing species from both adjoining
ecosystems and those unique to the ecotone itself.
2.Ecological Indicators:
1. Because ecotones are sensitive to environmental changes, they can serve as indicators of
ecological shifts, such as climate change or habitat degradation.
3.Species Movement:
1. Ecotones serve as important corridors for species migration, particularly for animals moving
between ecosystems in response to changes in food availability, breeding sites, or seasonal
conditions.
4.Ecological Stability and Adaptation:
1. The diverse mix of species and environmental conditions in ecotones can promote ecological
stability and increase the resilience of ecosystems to disturbances such as fires or floods.
Edge Effect in Ecotones:
•The edge effect refers to the tendency for greater biodiversity and species interactions in ecotones.
Species from both adjoining ecosystems converge in the ecotone, creating a rich and diverse
community. However, the edge effect can also lead to increased predation or competition, as species
from both ecosystems interact more frequently.
Field Surveys and Observations
•Description: This method involves direct observations and surveys of the community in its natural
environment to document the species present, their abundances, and their interactions.
•Techniques:
• Quadrat Sampling: Small, defined areas (quadrats) are randomly or systematically selected to study
species composition and density within them. Quadrats are particularly useful for studying plant
communities or immobile species.
• Transect Sampling: A line or tape measure (transect) is laid across a habitat, and species are recorded
at regular intervals along the line to study community composition and gradients.
• Point Counts: Commonly used for mobile species (e.g., birds), point counts involve standing at fixed
locations and recording all individuals seen or heard within a set distance.
2. Species Interaction Studies
•Description: This method focuses on understanding how species interact within a community, such as
predation, competition, mutualism, and facilitation.
•Techniques:
• Experimental Manipulation: Ecologists may remove or add species (e.g., predators or competitors) to
study the effects on other species and community dynamics.
• Mark-Recapture: Used to study species interactions, particularly in predator-prey relationships or
population dynamics of mobile species.
• Stable Isotope Analysis: Helps trace the flow of energy and nutrients through different species in a
community, giving insights into food webs and species interactions.
 4. Long-Term Ecological Monitoring
•Description: Long-term studies track the composition, structure, and function of communities over
extended periods, often across decades, to observe how communities respond to natural or human-induced
changes.
•Techniques:
• Permanent Plots: Areas that are revisited periodically to monitor changes in species composition,
diversity, and abundance.
• Remote Sensing and GIS: Satellite imagery and geographic information systems (GIS) allow for
large-scale and long-term monitoring of changes in habitats and communities over time.

Diversity and Composition Metrics

•Description: These methods focus on measuring the richness and diversity of species within a community
and comparing these across different communities or over time.
•Techniques:
• Species Richness: The total number of species in a community.
• Shannon-Wiener Index: A measure of species diversity that takes into account both richness and
evenness of species.
• Simpson’s Diversity Index: A measure of the probability that two individuals randomly selected from
a sample will belong to the same species.
The Shannon-Wiener Index (H'), also known as the Shannon Diversity Index, is a widely used measure of species diversity
in a community. It accounts for both species richness (the total number of species) and species evenness (the relative
abundance of different species). The index quantifies the uncertainty in predicting the species of a randomly selected
individual from a community, with higher values indicating greater diversity.
Formula:
The Shannon-Wiener Index is calculated using the following formula:
Interpretation of Shannon-Wiener Index:
•Higher values of H′ indicate greater species diversity.
Communities with both high species richness and
evenness will have higher Shannon-Wiener Index values.
•Lower values indicate lower diversity, suggesting either
fewer species or uneven distribution of individuals
among species.
Simpson’s Diversity Index is a measure used to quantify the biodiversity of a community by assessing species richness
(the number of species) and species evenness (the relative abundance of each species). It measures the probability that
two individuals randomly selected from a sample will belong to the same species. Simpson’s Index gives more weight to
dominant species, meaning communities with more even distribution of species will have higher diversity.
Formula:
The most commonly used form of Simpson’s Index is Simpson’s
Diversity Index (D), which can be calculated as:

Interpretation of Simpson’s Diversity Index:

•Values close to 1 indicate high diversity, meaning a low
probability that two individuals randomly selected from
the community will belong to the same species.
•Values close to 0 indicate low diversity, meaning one or
a few species dominate the community.
The term Biodiversity was the first coined by Walter G Rosen In 1986. Biological diversity known as
biodiversity represent the sum total of various life forms such as unicellular and multi cellular organisms
at various biological levels. It is the degree of variation of life forms within a ecosystem or Biome or entire
planet called biodiversity.
Types of Biodiversity:
Biodiversity can be categorized into three major types:
1. Genetic Diversity:
•Definition: Genetic diversity refers to the variety of genes within species. It includes variations in the genetic
makeup of individuals within a population, as well as between populations of the same species.
•Importance:
• Provides species with the ability to adapt to environmental changes (e.g., climate change, disease
resistance).
• Supports natural selection and evolutionary processes.
•Example: The different breeds of domesticated dogs or the variety of corn types grown in agriculture.
2. Species Diversity:
•Definition: Species diversity refers to the variety of species within a habitat or a region. It includes both species
richness (the number of species) and species evenness (the relative abundance of each species).
•Importance:
• Maintains ecological balance through complex species interactions like predation, competition, and
mutualism.
• Ensures ecosystem productivity and resilience.
•Example: A tropical rainforest with a wide range of species, from insects to large mammals, or a coral reef with
numerous fish species.
3. Ecosystem Diversity:
•Definition: Ecosystem diversity refers to the variety of ecosystems in a given geographic area. It encompasses
the different habitats, ecological communities, and environmental interactions.
•Importance:
• Ecosystem diversity supports a range of services, including nutrient cycling, water purification, and
climate regulation.
• Provides habitats for species and genetic diversity.
•Example: Forests, deserts, wetlands, grasslands, and coral reefs are different ecosystems that support various life
forms.

Uses of Biodiversity:
1. Ecological Services:
•Ecosystem Stability and Resilience: Diverse ecosystems are more stable and resilient to
environmental changes, disturbances, and disasters.
•Nutrient Cycling: Biodiversity plays a critical role in recycling nutrients such as nitrogen, carbon,
and phosphorus.
•Pollination: Many plant species rely on insects, birds, and other animals for pollination, ensuring
food production and plant diversity.
•Soil Formation and Protection: Microorganisms and plants contribute to soil formation and
erosion control, which is essential for agriculture and natural habitats.
2. Economic Benefits:
•Agriculture and Food Security: Biodiversity ensures a wide variety of crops and livestock,
providing food security. It also allows for genetic resources to improve crop resistance and
productivity.
•Pharmaceuticals: Many medicines are derived from plants, animals, and microorganisms found in
diverse ecosystems. For example, aspirin originates from willow trees, and certain cancer
treatments come from rainforest plants.
•Raw Materials: Forests, oceans, and other ecosystems provide timber, fish, fibers, and other raw
materials essential for industries and human livelihood.
•Ecotourism: Natural environments with high biodiversity, such as national parks and coral reefs,
attract tourists, contributing to local and global economies.

3. Cultural and Recreational Value:

•Spiritual and Aesthetic Value: Biodiversity enriches cultural practices and provides inspiration
for art, religion, and cultural identity. Many indigenous communities deeply value and depend on
local biodiversity for their traditions and livelihood.
•Recreational Use: Biodiverse ecosystems offer recreational activities like hiking, bird watching,
diving, and nature photography, which foster a connection to nature and well-being.
4. Climate Regulation:

•Carbon Sequestration: Forests, wetlands, and oceans absorb and store carbon dioxide, helping to regulate
global climate and mitigate climate change.
•Climate Adaptation: Diverse ecosystems provide natural buffers against extreme weather events, such as
mangroves protecting coastlines from storm surges.
5. Scientific and Educational Value:
•Research: Studying biodiversity helps scientists understand ecological processes, evolutionary biology, and
species interactions, leading to new discoveries.
•Education: Biodiversity provides a living laboratory for students and researchers to learn about biology,
conservation, and the environment.