Ecology
Created time January 9, 2025 634 PM
Segment
Contents
Meaning and definition
Branches of ecology
Factors Influencing Ecology
Biotic factors
Abiotic factors
Levels of ecological study
Population ecology
Age distribution in population
January 11, 2025
Patterns in age distribution(Age-sex pyramid)
Factors Affecting Population Growth
Patterns of population growth
Survivorship curve
Population stabilisation
Community ecology
Interspecific relations in a community
January 13, 2025
Ecotones
Examples of Ecotones in India
Keystone species
Ecological niche
Principle of competitive exclusion
Ecological guild
Ecological equivalent
Ecological succession
Types of Ecological Succession
Ecosystem ecology
Food Chain
Parasitic food chain
Detritus food chain
Grazing food chain(Aka predator food chain)
Ocean food chain
Meaning and definition
According to Elton(1927), the study of animals and plants in relation to their habits and habitats. According to Odum(1971), it
is the scientific study of structure and function of nature.
The term "ecology" was coined by German zoologist Ernst
Haeckel in 1866. He derived it from the Greek words
"oikos" meaning "house" or "dwelling place" and "logos"
meaning "study of."
Haeckel first introduced this term in his work "Generelle
Morphologie der Organismen" where he defined ecology
as the study of the relationship between organisms and
their environment.
Ernst Haeckel, German zoologist
Although Haeckel coined the term, the concepts of ecological relationships had been studied before him by various
naturalists and scientists. However, his formal definition helped establish ecology as a distinct scientific discipline.
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Branches of ecology
Autecology is the study of individual species in relation to Synecology is study of group of organisms or many
their environment. It is comparatively simpler. It studies: species or communities in relation to their environment.
It is comparatively complex. It studies ecological
Life history patterns
communities:
Morphology
Community structure
Taxonomy position
Species interactions
Population dynamics
Succession patterns
Species distribution
Other Important Branches
Population Ecology: Studies populations and their Landscape Ecology: Spatial patterns and processes
changes
Conservation Ecology: Preservation of species and
Community Ecology: Species interactions habitats
Ecosystem Ecology: Energy flow and nutrient cycling
Factors Influencing Ecology
Abiotic Factors Non-living components): Biotic Factors Living components):
Temperature and Climate Autotrophs, heterotrophs, decomposers
Light and Solar Radiation Competition between Species
Water Availability Predator-Prey Relationships
Soil Type and Composition Symbiotic Relationships
pH and Chemical Factors Human Activities
Atmospheric Conditions Disease and Parasitism
Biotic factors
Autotrophs are organisms that can produce their own
food using carbon through photosynthesis or
chemosynthesis. They are considered producers in an
ecosystem and form the foundation of food chains. The
organisms which use energy sources(oxidation of
inorganic substance, radioactive rocks, hydrothermal
vents, etc) other than sunlight for synthesis of foods
are called chemoautotrophs and this process is called
chemosynthesis.
Heterotrophs are organisms that cannot produce their own food and must obtain nutrition by consuming other
organisms. They can be further classified into herbivores (plant-eaters), carnivores (meat-eaters), omnivores (both
plant and meat-eaters), and detritivores (feed on dead organic matter).
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Decomposers are organisms that break down dead organic matter and waste materials, converting them into simpler
forms that can be reused in the ecosystem. They play a crucial role in nutrient cycling and are essential for maintaining
ecosystem health.
Abiotic factors
Light energy or sunlight is the primary source of energy to all the ecosystems. They are used by green plants during
photosynthesis. The factors of light which play important role on ecology are— quality of light, intensity of light and
length of light.
a Quality: plants absorb blue and red colour for conducting photosynthesis i.e. the photosynthetic ability or rate will
be the highest when plants are exposed to the blue and red light.
b Intensity: Because of the tilt of the earth different parts of earth receive different intensity of light at different times
of the year. It varies with season and latitude.
c Length Different plants respond differently to different lengths of the day. This response is known as
photoperiodism. Based on photoperiodism, plants are classified into three categories:
Type Definition Examples
Flower when days are longer than critical day length 12
Long-day Plants Wheat, spinach, radish
hours)
Flower when days are shorter than critical day length 12 Rice, chrysanthemum, coffee, cotton, soyabean,
Short-day Plants
hours) jowar
Day-neutral
Flower regardless of day length Tomato, cucumber, sunflower
Plants
Temperature: It influences ecology in various ways like weathering, erosion. Different plants and animals have different
tolerances for heat and cold.
Water: water is an important component in weathering or generation of soils and also erosion. The quality, quantity and
timing of water can affect the growth and survival of plants and animals. The terrestrial and fresh water ecosystems
requires animals and plants to evolve ways to adopt to the environment. Based on this the animals can be classified
into terrestrial, aquatic and amphibians. Plants can be clasified as Xerophytes(xeric conditions), mesophytes(moderate
water requirement) and hydrophytes(living under water).
Atmosphere: The atmosphere consists of various gases and factors that influence ecological processes:
Composition: Primarily nitrogen 78%, oxygen 21%, and other gases
Carbon dioxide: Essential for photosynthesis and affects global climate
Humidity: Affects transpiration rates and organism survival
Wind: Influences pollination, seed dispersal, and weather patterns
Air pressure: Changes with altitude affecting species distribution
Soil: It is a crucial abiotic factor that supports life and influences ecology through:
Soil texture: Determines water retention and root penetration
Soil pH Affects nutrient availability and microbial activity
Organic matter: Provides nutrients and improves soil structure
Mineral content: Essential for plant growth and development
Soil moisture: Influences plant growth and soil organism activity
Physiographic factors:
a Latitude: change in latitude will change temperature, rainfall, winds, etc and hence different plants and animals will
grow in different latitudes.
b Slope: the degree of slope changes the kind of plants and animals growing in that area. Slope affects run-off and
drainage and has huge influence on the moisture of the soil. Slope modifies the intensity of insolation and affects
the temperature of the soil. It also affects the erosion and humus content of the soil and hence affects the
vegetation.
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c Aspect: is the direction towards which the slope faces. It determines the amount of insolation received by hillside.
This influences the presence of plants and animals.
d Altitude aka elevation: higher elevation generally have cooler temperatures and limits the types of plants species
that can grow. Elevation also influences the precipitation and hence the kind of plants and animals present in that
area.
Living Fossils: These are species that have remained relatively unchanged for millions of years and closely
resemble their ancient ancestors found in fossil records. They have survived various extinction events and
maintained similar morphological characteristics over long periods. Some examples include:
Coelacanth: A prehistoric fish thought extinct until discovered alive in 1938
Horseshoe crab: Exists relatively unchanged for over 445 million years
Ginkgo biloba: A tree species dating back 270 million years
Nautilus: A marine mollusk that has survived since the Cambrian period
Tuatara: A reptile from New Zealand that has remained largely unchanged for 200 million years
Levels of ecological study
Ecological studies are conducted at different hierarchical levels, each focusing on different aspects of nature's
organization:
Individual Level: Studies single organisms, their physiology, behavior, and adaptations to their environment.
Population Level: Examines groups of individuals of the same species, including population dynamics, growth rates,
and genetic variation.
Community Level: Analyzes interactions between different populations living in the same area, including competition,
predation, and symbiosis.
Ecosystem Level: Studies the interactions between living organisms and their physical environment, including energy
flow and nutrient cycling.
Biosphere Level: Examines life and ecological processes on a global scale, including climate patterns, biogeochemical
cycles, and global species distribution.
Each level builds upon the previous one, creating a comprehensive understanding of ecological processes from
microscopic to global scales.
Population ecology
Itʼs a branch of ecology that studies the structure and dynamics of a population. Population is the smallest unit of
ecological analysis and is defined as a group of interbreeding and interactive individuals of the same species inhabiting the
same area at a given point of time.
Age distribution in population
In most types of population individuals are of different age. The proportion of individuals in each group is called the age
structure of the population. The ratio of various age groups in a population determines the current reproductive state and
thus anticipating the future. From the ecological point of view there are three major age groups—
Pre-reproductive Stage
Reproductive stage
Post-reproductive stage
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Patterns in age distribution(Age-sex pyramid)
The age-sex pyramid graphically represents the age and sex composition of a population. There are three main patterns:
Expansive pyramid: Shows a broad base that tapers towards the top. Indicates a growing population with high birth
rates and death rates. Common in developing countries.
Constrictive pyramid: Has a narrow base and bulges in the middle. Shows declining birth rates and an aging
population. Typical of developed nations.
Stationary pyramid: Nearly vertical sides with a more rounded top. Indicates relatively equal numbers across age
groups, suggesting stable population growth.
These patterns help ecologists understand population dynamics and predict future trends in species populations.
Stage 1 This pyramid indicates a rapidly growing population with both high birth and death rates. This stage is
characterized by poverty, illiteracy, lack of basic amenities, famines, wars, and absence of vaccination.
Stage 2 The pyramid takes a triangular shape. It shows high birth rates but decreasing death rates due to agricultural
revolution, government-provided basic amenities, and cures for diseases. Life expectancy increases, though reproductive
behaviors remain unchanged.
Stage 3 This pyramid indicates a stationary population. The growth rate becomes slow and stable, with reduced birth
rates and low death rates. Better medical facilities and modern contraceptives lead to increased longevity. The pyramid
takes a bell shape.
Stage 4 This pyramid indicates a declining population, with both low birth and death rates. This stage results from
urbanization, modernization, and changing societal values. The pyramid takes an urn shape.
Factors Affecting Population Growth
Population growth is influenced by various factors that can be broadly categorized into biotic and abiotic factors:
Natality Birth Rate): The number of births per unit time in the Immigration: The number of individuals
population. It's affected by: entering a population from other areas. Affects:
Fertility rates Genetic diversity
Age at first reproduction Population size
Reproductive period length Age structure
Number of offspring per reproduction Emigration: The number of individuals leaving
a population. Impacted by:
Mortality Death Rate): The number of deaths per unit time in
the population. Influenced by: Resource availability
Disease and predation Population density
Competition for resources Environmental conditions
Natural disasters These factors work together to determine whether
a population grows, remains stable, or declines
Age structure of population
over time.
Environmental Resistance: Factors that limit population
growth:
Food availability
Space constraints
Climate conditions
Competition with other species
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Term Definition Key Points
The actual reproductive
Measured by number of
Fertility performance of an individual or
offspring actually produced
population
The potential reproductive Maximum possible number of
Fecundity
capacity of an organism offspring under ideal conditions
Total number of births in a
Raw birth count without
Absolute Natality population during a given time
considering population size
period
Birth rate relative to the Usually expressed as births per
Real Natality
population size 1000 individuals per year
Patterns of population growth
The pattern of population growth can take two types of growth curve— exponential or geometric growth and logistic or
sigmoid growth.
Exponential growth: the population keeps increasing exponentially until some resources runs out or encounters some
other limitations. It takes J-shaped curve.
Logistic growth: a growth pattern where resources are limited, population growth has upper limit and is defined by
carrying capacity(in any natural ecosystem the biotic and abiotic factors work in such a way that the population must
have an upper size limit).
Survivorship curve
A survivorship curve is a graphical representation of the
survival pattern of a population over time, showing the
number or proportion of individuals surviving to different
ages. There are three main types of survivorship curves:
Type I Convex curve): Shows high survival in early
and middle life, followed by rapid decline in later life.
Common in large mammals, including humans in
developed nations. Few offsprings and high parental
care. They are called Iteroparus organisms.
Type II Diagonal curve): Shows a constant mortality rate throughout the organism's life span. Death occurs randomly.
Common in birds and small mammals.
Type III Concave curve): Shows very high mortality in early life, but high survival rate for those that survive this
period. Common in semelparous organisms called that produce many offspring but provide little parental care, like fish
and insects.
These curves help ecologists understand population dynamics, life history strategies, and evolutionary adaptations of
different species.
Population stabilisation
Population stabilization is regulated by two factors: density-dependent and density-independent factors. Density refers to
the concentration of individuals within a species in a specific geographical location. In nature, both these factors limit
population size and growth.
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Density-dependent: These biological factors regulate population growth rate based on population density. Examples
include predation, food availability, pathogens, and waste accumulation. As population density increases, the death
rate rises.
Density-independent: These physical, chemical, and geographical factors influence mortality regardless of population
density. Examples include temperature, floods, natural disasters, and pollution.
Community ecology
It is an assemblage of species population that has potential of interaction.
It is an interactive assemblage of species occurring together within a particular geographical
area whose ecological function and dynamics are some way interdependent.
Putman(1994)
Interspecific relations in a community
Interaction Type
Definition
Nature (+/0/-)
Clownfish and sea anemones
Lichen (algae and fungi)
Mycorrhizae(fungus and plant
roots)
Mutualism Both species benefit from the
Rhizobium bacteria and
(+/+) interaction
legume roots
Fig tree and fig wasp
Coral polyps(cnidarians) and
zooxanthalae
Both species benefit with the
Bees and flowers
Proto-cooperation association but their relationship
Crow and buffaloes
is non-obligatory
Lions and tigers competing for
prey
Plants competing for sunlight
Competition Both species compete for and nutrients
(-/-) limited resources Birds competing for nesting
sites
Different species of butterflies
competing for nectar
Owls hunting mice
Predation One species feeds on another Cheetahs preying on gazelles
(+/-) species Spiders catching insects
Whales feeding on krill
Tapeworms in human
intestines
Parasitism One species lives on/in and Ticks on mammals
(+/-) derives nutrients from another Mistletoe on trees
Cuckoo birds laying eggs in
other birds' nests
Orchids growing on trees
Remora fish attached to
Commensalism One species benefits while
sharks
(+/0 other is unaffected
Cattle egrets following cattle
Barnacles on whales
Amensalism One species is harmed while Penicillium fungi inhibiting
0/-) other is unaffected bacterial growth
Large trees shading smaller
plants
Sheep trampling grass
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Interaction Type
Definition
Nature (+/0/-)
Black walnut trees releasing
juglone
Squirrels and earthworms
Neutralism Neither species affects the Bears and butterflies
0/0 other Penguins and kangaroos
Cacti and zebras
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Ecotones
An ecotone is a transition area between two different biological communities or ecosystems. It is where two communities
meet and integrate, creating unique environmental conditions different from either community.
Key characteristics of ecotones:
Edge effect: Ecotones often support greater biodiversity than either of the adjacent communities
Unique species: Some species are found only in these transition zones
Dynamic nature: These areas are sensitive to environmental changes and can shift over time
Gradient changes: Environmental factors gradually change across the ecotone
Common examples of ecotones include:
Forest-grassland transitions: Areas where forests gradually blend into grasslands
Shorelines: Transitions between aquatic and terrestrial ecosystems
Mangrove swamps: Transitions between marine and freshwater environments
Treeline: The boundary between forest and alpine tundra in mountains
Ecological significance of ecotones:
Biodiversity hotspots: Support species from both adjacent communities plus unique ecotone species
Environmental indicators: Changes in ecotones can signal broader environmental changes
Wildlife corridors: Often serve as important migration routes and wildlife passages
Research value: Provide opportunities to study species interactions and adaptation
Examples of Ecotones in India
Sundarbans Mangrove Forest: A unique ecotone between marine and freshwater ecosystems in West Bengal, where
rivers meet the Bay of Bengal
Western Ghats: Transition zones between mountain forests and coastal plains, creating diverse microhabitats along
the elevation gradient
Thar Desert Edge: The boundary between the arid desert and semi-arid regions of Rajasthan, showing gradual
changes in vegetation
Brahmaputra Valley: Transitions between riverine ecosystems and grasslands, supporting unique flora and fauna
Eastern Himalayan Foothills: Ecotones between mountains and plains, characterized by distinct subtropical vegetation
patterns
These Indian ecotones are particularly important for biodiversity conservation as they often serve as critical wildlife
corridors and harbor several endemic species.
Keystone species
A keystone species is an organism that has a disproportionately large effect on its environment relative to its population
size. A small impact on keystone species could cause major disruption for the whole ecosystem and the ecosystem may
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