INDEX

1. Theory 3 - 68

2. Exercise 69 - 79

3. Answers Key 80
ECOLOGY 3

Ecology

1. Introduction
An ecosystem is a functional unit of nature, where living organisms interact among themselves and also with the surrounding
physical environment. The term ecosystem was introduced by A.G. Tansley (1935).
An ecosystem is an open system. It receives input in the form of solar energy and inorganic matter, which results in the synthesis of
organic food. Energy from food passes through various components of the ecosystem. Each component as well as the whole
ecosystem gives out energy as well as waste matter. It is called output.
Matter circulates in the ecosystem, whereas energy is lost. Therefore, a regular input of energy is essential for maintaining
any ecosystem.

Fig 14.2 Matter circulates in the ecosystem and energy is lost

1.1 Types of Ecosystem

Ecosystems vary greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a global
ecosystem, as a composite of all local ecosystems on Earth.
Ecosystems are broadly divided into two basic categories, namely the terrestrial and the aquatic.

Ecosystem

Aquatic/Water
Terrestrial/Land
Pond, lake, wetland, river, and
Forest, grassland, and desert
estuary
4 ECOSYSTEM

Fig 14.3 Terrestrial ecosystem

Fig 14.4 Marine ecosystem

Similarly, on the basis of human interference, ecosystems are of two types:

Ecosystem

Natural Man-made/Anthropogenic/Artificial
It develops in nature without human support or It is created and maintained by human beings. E.g.,
interference. E.g., forest, marine ecosystem. crop fields, garden, aquarium, spacecraft.

Aquarium Crop field

Fig 14.5 Man-made ecosystems

FUN FACT:
Agriculture or agrosystem is the largest man-made ecosystem.
ECOLOGY 5

2. Ecosystems - Structure and Functions

2.1 Structure
Interaction of biotic and abiotic components results in a physical structure that is characteristic for each type of ecosystem. The
various features of an ecosystem structure are:

Species
Composition

Standing State Stratification

Trophic
Standing Crop
Structure

Fig 14.6 Structural features of an ecosystem

 Species Composition:
Identification and enumeration of plant and animal species of an ecosystem give its species composition. It differs from one
ecosystem to another depending upon geography, topography, and climate. Maximum species composition occurs in tropical
rain forests and coral reefs. On the other hand, minimum species composition occurs in deserts and arctic regions.

Fig 14.7 Coral reefs: Maximum species composition Fig 14.8 Desert: Minimum species composition
 Stratification:
Vertical distribution of different species occupying different levels is called stratification.
E.g., the tropical rainforest has 5-7 strata, with emergent tall trees as the top vertical layer followed by a dense canopy of tall
trees, short trees, shrubs, and grasses (ground layer) (lowermost layer).
Stratification helps in the accommodation of large numbers and types of plants in the same area. It provides a number of
microhabitats and niches for various types of animals. Stratification is absent or rare in deserts.
6 ECOSYSTEM

Fig 14.9 Vertical Stratification in Tropical Rainforests

 Trophic Structure:
Ecosystem structure is influenced by the type, amount, and level at which food is available. Producers form the first trophic
level (T1), herbivores constitute the second trophic level (T2). Carnivores can have 1-3 trophic levels (T3, T4, T5). Each
ecosystem has specific food chains and food webs. E.g., grazing food chain in grassland.

Fig 14.10 Trophic structure

 Standing Crop:
Each trophic level has a certain mass of living material at a particular time called the standing crop. The standing crop is
expressed as the mass of living organisms (biomass) or the number of living organisms in a unit area of an ecosystem. The
biomass of a species is measured in terms of fresh or dry weight. Measurement of biomass in terms of dry weight is more
accurate. This is because the fresh weight is liable to be influenced by seasonal moisture differences.

Fig 14.11 Standing Crop

 Standing State:
ECOLOGY 7

It is the amount of inorganic nutrients present at any time in the soil/water of an ecosystem. It is not fixed and tends to vary
from ecosystem to ecosystem and season to season. The standing state determines the minerals available to the plants for growth.

Fig 14.12 Standing state

Differences between Standing Crop and Standing State

Standing Crop Standing State

It is the amount of biomass present in an ecosystem. It is the amount of inorganic nutrients found in an ecosystem.

It represents the entire living matter. It represents part of non-living matter.

It circulates between biotic and abiotic components of the

There is no circulation.
ecosystem.

Biomass is continuously synthesized and consumed. It is regularly depleted and replenished by living matter.

2.2 Functions
All the components of the ecosystem function as a unit with a number of delicately balanced and controlled processes. Plants
withdraw biogenetic nutrients from the soil. The nutrient availability depends on the decomposition and mineralization of organic
detritus. Animals found in the ecosystem are delicately balanced by the number of herbivores and the degree of herbivory.
Four important functional aspects of an ecosystem are as follows:
8 ECOSYSTEM

Productivity

Nutrient Cycling Decomposition

Energy flow

Fig 14.13 Functional aspects of an ecosystem

3. Components of Ecosystem
An ecosystem is made up of two main types of components: Biotic and Abiotic.

Components of an Ecosysten

Abiotic Biotic

Fig 14.15 Components of an Ecosystem

3.1 Abiotic Components

ECOLOGY 9

The non-living factors or the physical environmental factors prevailing in an ecosystem constitute the abiotic components. Abiotic
factors include the following:

Abiotic Components

Climatic factors Edaphic factors Topographic factors

 Climatic factors: It includes light, temperature, water, precipitation, wind, humidity, air currents.
 Edaphic factors: It includes factors related to the composition and structure of the soil, including its physical and chemical
properties.
 Topographic factors: It includes factors that are related to physical features of the earth such as valleys, slopes, mountains,
plains, etc.

Fig 14.16 Abiotic factors

3.2 Biotic Components

Different types of living organisms in an ecosystem are known as biotic components.

Fig 14.17 Biotic factors

Biotic factors are linked amongst themselves with food and a number of other relations. Living organisms are of three types:
producers, consumers, and decomposers.
10 ECOSYSTEM

Biotic Components

Producers Consumers Decomposers

Primary

Secondary

Tertiary

Top
3.1 Producers
 They are photosynthetic green plants that entrap solar energy through chlorophyll to manufacture organic food from inorganic
raw materials. Hence, they are known as autotrophs.
 They are also known as transducers or converters because they can change light energy into chemical energy stored in the
bonds of sugars.

Fig 14.18 Producers

 In a terrestrial ecosystem, major producers are herbaceous and woody plants.
 Likewise, producers in an aquatic ecosystem are various species like phytoplankton, algae, and higher plants.

3.2 Consumers
 They are animals that cannot synthesize their own food and are directly/indirectly dependent on producers for their survival.
Hence, they are known as heterotrophs.
 They are also called phagotrophs because they ingest their food.
 They are of the following types:
 Primary Consumers (PC) or First Order Consumers or Herbivores: They directly feed on producers. They are also
known as key industry animals and convert plant matter into animal matter.
Terrestrial ecosystem: Grasshopper, cow, deer, etc.
Aquatic ecosystem: Molluscs, tadpole, mosquito larvae, etc.
ECOLOGY 11

Fig 14.19 Cattle Fig 14.20 Tadpoles

 Secondary Consumers (SC) or Second Order Consumers or Primary Carnivores: They feed on herbivores.
Terrestrial ecosystem: Toad, spiders, lizards, centipedes, insectivorous birds, etc.
Aquatic ecosystem: Hydra, frog, some fishes, etc.

Fig 14.21 Hydra Fig 14.22 Spider

 Tertiary Consumers (TC) or Third Order consumers or Secondary Carnivores: They are carnivores that feed on
secondary consumers. E.g., large fishes like Pike (aquatic ecosystem), wolf, snakes (terrestrial ecosystem). Fourth order or
quaternary consumers that prey upon secondary carnivores may also exist.

Fig 14.23 Pike fish Fig 14.24 Wolf

 Top carnivores: The carnivores that are not eaten by others are known as top carnivores or apex predators. They may
belong to the category of primary, secondary, or tertiary carnivores. E.g., tiger, lions, panther, hawk, peacock, etc.
12 ECOSYSTEM

Fig 14.25 Lion Fig 14.26 Tiger

3.3 Decomposers
 They are saprophytic microorganisms that obtain their food material from organic matter present in the remains of dead animals
and plants by secreting digestive enzymes that convert complex organic substances into simpler substances.
 A part of the digested organic matter is assimilated by the microorganisms and the remaining part is broken down into simpler
inorganic substances for recycling.

Complex organic substances Simple organic substances Inorganic compounds

 Decomposers bring a cyclical exchange of materials between the biotic community and the environment. Hence, they are
considered to be very essential components of an ecosystem.
 Since they are capable of degradation and removal of dead bodies of organisms, they are also known as reducers.
 They are also known as micro-consumers because of their small size.
 E.g., fungi, bacteria, flagellates.
 Functions of decomposers:
 They reduce the organic waste of the earth. Hence, they are natural scavengers.
 They replenish the minerals in the soil naturally. These minerals are essential for plant growth and thus
ecosystem maintenance.
Some workers differentiate two more categories of living organisms amongst the biotic components of an ecosystem. They are
as follows:
 Scavengers or Detrivores:
 Animals that feed on dead bodies of other organisms are known as scavengers or detrivores.
 They clean the earth of organic garbages and help in the quick disposal of dead bodies.
 In the process, they leave small fragments for decomposers.
 E.g., Crows, Vultures, Carrion Beetles, Earthworms, Termites, etc
ECOLOGY 13

Vulture Carrion Beetles

Earthworms Termites
Fig 14.27 Scavengers/Detrivores

 Parasites: They belong to diverse groups. E.g., bacteria, fungi, protozoans, worms, etc. Every type of living being can be
attacked by parasites.

Bacteria Fungi
Fig 14.28 Parasites

DID YOU KNOW?

Detritivores ingest and digest dead organic matter internally whereas decomposers directly absorb nutrients through external
chemical and biological processes.
14 ECOSYSTEM

Fig 14.29 Relationship between biotic components of an ecosystem

Components of an ecosystem

Components of an Ecosystem

Abiotic Biotic

Producers Consumers Decomposers

Climatic factors
(Autotrophs) (Heterotrophs) (Saprotrophs)

Primary
Edaphic factors

Secondary

Topographic factors
Tertiary

Top
ECOLOGY 15

Differences between Biotic and Abiotic Components

Biotic Components Abiotic Components

They represent non-living materials and factors of the

They represent living components of an ecosystem.
ecosystem.

They include producers, consumers, and decomposers. They include inorganic nutrients and physical factors.

They depend on abiotic factors for survival and growth. They determine the livability of biotic components.

Example- plants, animals, microbes. Example- temperature, water, light, soil.

3.4 A Pond Ecosystem

A pond or lake is a natural aquatic ecosystem that is self-sustaining and complete. A pond is a shallow water body that comprises
all the structural components that work as a unit and shows all the four functional aspects of the ecosystem.

Fig 14.30 A Pond Ecosystem

3.4.1 Structure of a Pond Ecosystem
It comprises both abiotic and biotic components.
Abiotic Components:
 They include water with all the dissolved inorganic and organic substances and the rich soil deposit at the bottom of the pond.
 The solar input, the cycle of temperature, day-length, and other climatic conditions regulate the rate of function of the
entire pond.
Biotic Components:
 They include producers, consumers, and decomposers.
 Producers are autotrophs that include phytoplankton, some algae, and the floating, submerged, and marginal plants found at
the edges.
 The consumers include zooplankton, free-swimming, and bottom-dwelling animals.
 Consumers are differentiated into herbivores and carnivores.
16 ECOSYSTEM

 Herbivores include zooplankton, larvae, tadpole, and some fish.

 Primary carnivores include water scorpions, water beetle, dragonfly larvae, Hydra, and some fish.
 Secondary carnivores include larger fish and many water birds.
 The decomposers are the fungi, bacteria, and flagellates especially abundant in the bottom of the pond.

3.4.2 Functions of a Pond Ecosystem

This system performs all the functions of any ecosystem and of the biosphere as a whole.

Autotrophs convert inorganic materials

into the organic matter with the help of
the radiant energy of the sun. This is
primary productivity.

Autotrophs are consumed by

Minerals are released in the process
heterotrophs which build up their
that become available to autotrophs
own organic matter. This is
for reuse.
secondary productivity.

Decomposers act upon organic

wastes and dead organisms.

These events are repeated over and over again. Hence, there is cycling and recycling of matter. However, there is a unidirectional
movement of energy.

4. Productivity of Ecosystem

 A constant input of solar energy is the basic requirement for any ecosystem to function and sustain.
ECOLOGY 17

 The rate of biomass production at any trophic level per unit area in unit time is called productivity.
 It is expressed in terms of weight (g/m2/yr) or energy (kcal/m2/yr).
 It is divided into two types: Primary productivity and Secondary Productivity.

4.1 Primary Productivity

 It is defined as the amount of energy accumulation in green plants as biomass or organic matter produced per unit area over a
time period through photosynthesis.
 Primary productivity is of two types: Gross Primary Productivity and Net Primary Productivity.
 Gross primary productivity (GPP): It is the total amount of solar energy captured and total organic matter or biomass
manufactured by producers through photosynthesis per unit time per unit area.

Fig 14.31 Sugar produced is the biomass (GPP)

 Net primary productivity (NPP):

 NPP is the total energy or biomass stored by the producers per unit area per unit time.
 It can also be defined as the available biomass for consumption by heterotrophs (herbivores and decomposers).
 It is equal to organic matter synthesized by photosynthesis (GPP) minus utilization in respiration (R) and other losses.
18 ECOSYSTEM

NPP = GPP – R

Fig 14.32 Primary Productivity

Differences between Gross Primary Productivity and Net Primary Productivity

4.2 Secondary Productivity

 It is defined as the rate of formation of new organic matter by consumers.
 Consumers are heterotrophic. They obtain readymade organic matter.
 A part of this organic matter consumed is used to obtain energy in respiration and some is wasted as fecal matter.
 The rest is assimilated and used in the growth and bodybuilding of consumers.
 Gross secondary productivity (GSP) is the total energy/biomass assimilated by consumers. It is calculated by subtracting the
mass of fecal loss from the mass of food eaten.
GSP = Food eaten - Fecal loss
 Net secondary productivity (NSP) is the gain by consumers in energy or biomass remaining per unit area per unit time after
respiratory losses. It is calculated by subtracting the respiratory losses (R) from GSP.
NSP = GSP - R
 Respiration loss is about 20% for autotrophs, 30% for herbivores, and up to 60% for carnivores. Thus, net productivity decreases
with each trophic level.
ECOLOGY 19

Fig 14.33 Secondary Productivity

Please Note: NPP should not be confused with total biomass or standing crop of autotrophs. NPP is the rate at which biomass
accumulates. Standing crop is the biomass present in the ecosystem.

Primary Productivity Secondary Productivity

It is the rate of synthesis of organic matter by producers. It is the rate of synthesis of organic matter by consumers.

It is comparatively quite high. It is small and decreases with the rise of trophic levels.

It is due to the synthesis of fresh organic matter from

It is due to the synthesis of organic matter from organic matter.
inorganic raw materials.

4.3 Factors Affecting Primary Productivity

Several biotic and abiotic factors affect primary productivity.
 Solar Radiations:
 Sun is the ultimate source of energy. Maximum light is available in the tropics while poles receive minimum light.
 Due to this, photosynthesis is maximum and NPP is highest in the tropics.
 In aquatic ecosystems, productivity is less than in terrestrial ecosystems.
 In an aquatic ecosystem, light is the limiting factor for the productivity of the organisms because most of the organisms are
dependent on light which is not available at the deep-sea level.

Fig 14.34 Photosynthesis is maximum and NPP is highest in the tropics

20 ECOSYSTEM

 Temperature:
 Temperate forests have lesser productivity than tropical rainforests because the colder climates limit the
primary productivity.
 Arctic and alpine zones have very less productivity.

Fig 14.35 Alpine zones have very less productivity

 Moisture:
 Humidity and rain increase the productivity of an ecosystem.
 Productivity decreases with water scarcity.
 Deserts have the lowest primary productivity.

Fig 14.36 Deserts have the lowest primary productivity

 Nutrients:
 Nutrients are essential for the growth of producers.
 Nitrogen is deficient in oceans that limits the productivity in marine ecosystems.
 Desert soils are also deficient in nutrients and thus have low productivity.
 Estuaries and coral reefs are highly productive as nutrient supply is rich.
 Photosynthetic efficiency of Producers:
 C4 plants are more productive than C3 plants.
 Sugarcane is the most productive crop being efficient in trapping light.
ECOLOGY 21

Fig 14.37 Sugarcane (C4 plant) Fig 14.38 Wheat (C3 plant)
Productivity of Biosphere
 The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of organic matter.
 Of this, despite occupying about 70% of the surface, the productivity of the oceans is only 55 billion tons and for the terrestrial
ecosystem is 115 billion tons.

5. Decomposition

Fig 14.39 Decomposition

 It is the physical and chemical breakdown of complex organic matter into inorganic substances, like carbon dioxide, water, and
nutrients with the help of organisms called decomposers.
 In terrestrial ecosystems, the upper layer of the soil is the main site of decomposition.
 Organic remains (dead plant parts, animal remains, and excretions) are known as detritus which is the raw material
for decomposition.
 It is of two types:

Detritus

Above-ground Detritus
Below-ground Detritus
Leaf litter, Dried plant parts,
Dead roots, Underground dead animals
Animal remains, animal excreta
22 ECOSYSTEM

Differences Between Detritus and Litter

Detritus Litter

1. It is remains of plants and animals i.e., it is freshly 1. Litter is mostly dried fallen plant matter.
deposited organic matter.

2. It is of two types, above ground and below ground. 2. It is above ground.

5.1 Process of Decomposition

Decomposition completely disposes off the whole detritus. It helps in the recycling of nutrients and creates space for more
organisms. Three types of processes are involved in decomposition.
 Fragmentation
 Catabolism
 Leaching
All these processes occur simultaneously.
5.1.1 Fragmentation
Small invertebrates called detritivores contribute to the breakdown of large pieces of detritus into smaller fragments. E.g.,
earthworms, termites, ants, millipedes, snails, etc. Some part of the detritus is eaten by them which comes out in a highly pulverized
state in their feces. Due to fragmentation, the leftover detritus has a larger surface area.

5.1.2 Catabolism
Decomposers (bacteria, fungi, etc.) degrade detritus into simpler inorganic substances by secreting digestive enzymes over the
fragmented detritus.

Fig 14.41 Fungi on Detritus

5.1.3 Leaching
A part of soluble substances (inorganic nutrients, sugars) present in fragmented and decomposing detritus, get leached to deeper
layers of soils by percolating water. They get precipitated as unavailable salts.

Fig 14.42 Leaching

ECOLOGY 23

Fig 14.43 Diagrammatic representation of decomposition cycle in a terrestrial ecosystem

5.1.4 Humification and Mineralization

Decomposition process gives rise to two types of substances: Humus and inorganic nutrients (minerals). Processes involved in their
formation are called humification and mineralization, respectively.

Humification
 It is the process of partial decomposition of detritus to form humus.
 Humus is a dark-colored amorphous substance rich in lignin, cellulose, tannins, etc.
 It is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
 Being colloidal in nature, it serves as a reservoir of nutrients.

Fig 14.44 Humus

Mineralization
 It is the release of inorganic substances (e.g., CO2, H2O, minerals) from organic matter (humus).
 They become available to plants for utilization in the synthesis of organic matter.
 The process is slow because of trapping in humus and immobilization in decomposers/detrivores. This prevents their washing
out or leaching.
 Nutrients immobilized in decomposer microbes and detrivores are again exposed to humification and mineralization after the
death of these organisms.
24 ECOSYSTEM

Fig 14.45 Minerals

Fig 14.46 Processes involved in the decomposition of detritus

Differences between Production and Decomposition

Differences between Detrivores and Decomposers

ECOLOGY 25

5.2 Factors Affecting Decomposition

Rate of decomposition of detritus is controlled by a number of factors:

 Chemical nature of detritus

 If detritus is rich in lignin and chitin, the rate of decomposition is very slow.
 On the other hand, decomposition is rapid if detritus is rich in nitrogen and water-soluble substances (like sugars).
 Cellulose decomposition takes time.

 Temperature

 A soil temperature of 25℃ or more increases the rate of decomposition.

 Under low-temperature conditions (<10℃) of soils, the rate of decomposition is very slow (it may take up to several years
or even decades to decompose).
 As a result, in many temperate forests, detritus piles up at the ground level.

 Soil pH

 Neutral and slightly alkaline soils are rich in detritivores, earthworms, and decomposer microbes.
 Acidity decreases the number of detritivores and earthworms.
 Decomposer microbes occur in slightly acidic soils but their number begins to fall with a rise in acidity.
 Hence, decomposition of detritus is quite slow in acidic soils.
 Moisture
 An optimum moisture helps in the rapid decomposition of detritus.
 Reduction in moisture leads to a slow rate of decomposition.
 In tropical deserts, because of prolonged dryness, the rate of decomposition is very low, despite having high temperatures.
 Aerobic conditions
 Decomposition is largely an oxygen-requiring process. Hence, aerobic conditions are essential for the activity of
decomposer organisms.
 Anaerobiosis reduces decomposition and causes piling up of detritus.

6. Energy Flow
 Energy flow is a sequential process of the movement of energy in an ecosystem through a series of organisms.
 The Sun is the only source of energy for all ecosystems on Earth (except for the deep sea hydro-thermal ecosystem).
26 ECOSYSTEM

 Of the incident solar radiation, less than 50% of it is photosynthetically active radiation (PAR).

DID YOU KNOW?

Photosynthetically Active Radiation (PAR) is the amount of light available for photosynthesis. It is light in the 400 to 700 nm
wavelength range. PAR changes seasonally and varies depending on the latitude and time of day.

 Plants and photosynthetic bacteria (autotrophs), fix Sun’s radiant energy to make food from simple inorganic materials.
 Plants capture only 2-10% of the PAR (1-5% of total solar energy) for the synthesis of organic matter (Gross primary
productivity) and this small amount of energy sustains the entire living world.
 Around 20% of the total solar energy is consumed in respiration. Hence, net capture of energy (Net primary productivity) is
0.8-4% of incident radiation (1.6-8% of PAR).

Fig 14.47 Fate of solar energy incident on vegetation

 Energy does not remain trapped permanently in any organism.

 Solar energy captured by plants flows through different organisms of an ecosystem.
 All organisms are dependent for their food on producers, either directly or indirectly.
 Herbivores feed on producers.
 Part of the food energy is wasted in digestion and assimilation. Some of the assimilated food is broken down to release energy
for performing body activities. A very small portion becomes part of the body of the herbivore.
 Herbivores are eaten by primary carnivores which are further eaten by secondary carnivores, and so on.
 At every step, a lot of energy is wasted.
 Hence, there is a unidirectional flow of energy from the sun to producers and then to consumers.

Solar radiations Producers Herbivores Carnivores

ECOLOGY 27

Fig 14.48 Unidirectional flow of energy

 At each step, the energy becomes available to detrivores and decomposers after the organism dies or as fecal matter.

Fig 14.49 Energy flow in an ecosystem

Energy flow is in accordance with the laws of thermodynamics
 According to the first law of thermodynamics, energy is neither created nor destroyed, but can be transformed from one form
to another. Similarly, the energy of sunlight is transformed into the energy of food and heat.
 According to the second law of thermodynamics, no energy transfer occurs unless and until it is accompanied by degradation
or dissipation of energy from concentrated to dispersed form. Similarly, energy transfer from one organism to another is
accompanied by degradation and loss of a major part of food energy as heat. The energy of food is in concentrated form while
it is in a highly dispersed form as heat.

6.1 Lindeman’s Law

 The law was proposed by Lindeman in 1942.
 It is also known as the Ten Percent Law of Energy Transfer.
 This law states that the transfer of energy from one trophic level to another is accompanied by a loss of energy at each level
or step.
 The amount of energy decreases at successive trophic levels.
 Organisms at each trophic level depend on those at the lower trophic level for their energy demands.
 When a producer (plants) are eaten by a herbivore, about 10% of energy in the food is fixed into animal flesh while 90% is
consumed in ingestion, respiration, maintenance of body heat, and other processes.
 Similarly, when a carnivore feeds on this herbivore, only 10% of energy is fixed in the carnivore.
 Therefore, only 10% of the energy is transferred to each trophic level from the lower trophic level.
28 ECOSYSTEM

Carnivore II
(1 kcal)

Carnivore I
(10 kcal)

Herbivore
(100 kcal)

Producer
(1000 kcal)

Fig 14.50 10% Law of Energy Transfer

 As a result, the residual energy decreases drastically within 2-3 trophic levels. Hence, an ecosystem can support only a limited
number of trophic levels hardly, 3-5.
 The loss of energy in respiration increases gradually with each successive trophic level. It is 20%, 30%, and 60% respectively
at the producer, consumer, and top carnivore level.

Fig 14.51 Energy flow through different trophic levels

7. Food Chain and Food Web

7.1 Food Chain
 A food chain is a sequence of populations or organisms of an ecosystem through which the energy of food passes with each
member becoming the food of a latter member of the sequence.
ECOLOGY 29

Fig 14.52 Food Chain

 Food Chains are of three types:

Types of Food Chain

Grazing Detritus Parasitic

7.1.1 Grazing Food Chain (GFC)

 It is the most common food chain.
 It is also called the predator food chain as predation occurs at every step.
 In an aquatic ecosystem, GFC is the major conduit for energy flow.
 The source of energy for such a food chain is the sun.
Composition
 It consists of producers, consumers, and decomposers.
 The decomposers are often omitted as they operate at all levels of the food chain.
 Consumers are often of 3-5 types – first-order (primary), second-order (secondary), third-order (tertiary), fourth-order
(quaternary) consumers.
 Producers:
 They are autotrophic organisms that fix up the solar energy and manufacture their own food from inorganic raw material
by photosynthesis. Hence, they form the base of the food chain.
 Part of the food synthesized by them is used up in providing energy for various body activities and in overcoming entropy
while the rest is used in bodybuilding.
 Part or whole of the latter enters the food chain as food for consumers.
 Primary Consumers or Herbivores:
30 ECOSYSTEM

 These are animals that feed on green plants or their products.

 E.g., grasshoppers and several other insects, rabbit, hare, field mouse, deer, zooplankton, tadpoles, etc.
 A part of food eaten by herbivores becomes a constituent of their body while a major part is consumed in energy production
for fuelling various body activities.
 Secondary Consumers or Primary Carnivores:
 These are animals that feed on herbivores.
 E.g., frogs, predator insects, several birds, fishes, wild cats, etc.
 A part of flesh obtained from herbivores is used in bodybuilding by primary carnivores while the rest is consumed in
providing energy for various life processes.
 Tertiary Consumers or Secondary Carnivores:
 These are animals that feed on secondary consumers.
 E.g., wolf (feeds on fox), snake (prey upon frog).
 Top Carnivores:
 They are the last order consumers or carnivores which are not preyed upon by other animals owing to their size,
ferociousness, and agility.
 E.g., shark, crocodile, eagle, etc.
Examples of GFC
 Food Chains on Land:
 Grass → Grasshopper → Frog → Snake → Peacock/Falcon
 Vegetation → Rabbit → Fox → Wolf → Tiger
 Vegetation → Insect → Predator Insect → Insectivorous Bird → Hawk

Fig 14.53 Grassland ecosystem

 Food Chains in Water (Pond)

 Phytoplankton → Zooplankton → Small Crustaceans → Predator Insects → Small Fish → Larger Fish → Crocodile
 Phytoplankton → Zooplankton → Small Crustaceans → Predator Insects → Small Fish → Kingfisher/Stork
ECOLOGY 31

Fig 14.54 Aquatic ecosystem

7.1.2 Detritus Food Chain (DFC)

 It begins with detritus or dead organic matter.
 Detritus is eaten by three types of organisms - Scavengers (e.g., Crow, Vultures), detritivores (e.g., earthworms, termites, larvae
of blowfly maggots), and decomposers (bacteria and fungi).
 As a result, the food energy present in detritus passes into these organisms.
 Detrivores and decomposers are consumed by smaller carnivores which in turn become food for larger carnivores and so on.
 In a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC.
 A common DFC with earthworm as detritivore is:

Fig 14.55 Detritus Food Chain

7.1.3 Parasitic Food Chain (PFC)

 It is also known as the auxiliary food chain.
 It begins with the host and usually ends in a parasite.
 Examples:
 Producer → Parasite
32 ECOSYSTEM

 Herbivore → Parasite
 Carnivore → Parasite
 Example: Grass → Cattle → Pneumococcus.
 Some parasites can further be consumed by hyperparasites

Fig 14.52 Parasitic Food Chain

Differences between Grazing Food Chain and Detritus Food Chain

Grazing Food Chain Detritus Food Chain

It starts with the sun as the main source of It starts with the dead remains of organisms (detritus) as the main source of
energy. energy.

Producers form the base of the food chain. Detritivores and decomposers form the base of the food chain.

It adds energy to the ecosystem. It retrieves food energy from detritus and prevents its wastage.

It binds up inorganic nutrients into organic

It releases inorganic nutrients bound in organic matter to the cycling pool.
matter.

It provides organic matter to the detritus food

It provides inorganic nutrients to the grazing food chain.
chain.

7.2 Food Web

 Detritus food chain may be connected with the grazing food chain at some levels: some of the organisms of DFC are prey to
the GFC animals, and in a natural ecosystem, some animals like cockroaches, crows, etc., are omnivores.
 These natural interconnections of food chains make it a food web.
ECOLOGY 33

Fig 14.53 Food Web

 Food web increases the stability of an ecosystem by providing alternate sources of food to different organisms and allowing the
endangered population to grow in size.
 An animal may prefer a particular prey but if the prey has a small population, the predator may feed on some other prey.
 A single animal may be eaten by different animals and thus, different food chains get interconnected and one animal may be a
link in more than one food chain.
 Feedback checks operate in food webs that keep the populations of different species nearly constant.
 Food webs operate because of taste preference for a particular food and unavailability of food.
 One animal may feed upon organisms belonging to different positions in the food chain. E.g., snakes may feed upon mice
(herbivores) and frogs (carnivores), jackals are both carnivores and scavengers. Sparrow is a primary consumer when it eats
seeds, fruits, etc., and a secondary consumer when it eats insects and worms.

Fig 14.54 Terrestrial Food Web

34 ECOSYSTEM

Fig 14.55 Aquatic Food Web

8. Trophic Levels
Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic
level. The number of trophic levels is equivalent to the number of steps in the food chain. The two fundamental trophic levels are
producers and consumers.
A fundamental similarity of the organisms at all trophic levels is that they use a part of food in bodybuilding while a major part of
it is consumed in the liberation of energy during respiration.

Fig 14.56 Trophic levels in the ecosystem

 Producers belong to the first trophic level or T1.
 Herbivores or consumers of the first order constitute the second trophic level or T2.
 Consumers of the second-order or primary carnivores form the third trophic level or T3.
 There may be 2-3 levels of carnivores.
 The top carnivores belong to T4 or T5 trophic level.
 Decomposers form the last or detritus trophic level (e.g., T6). When an organism dies, it is converted to detritus or dead biomass
that serves as an energy source for decomposers.
 Parasites do not have any fixed trophic level as they feed on producers, herbivores as well as carnivores of various levels. E.g.,
aphids, ticks, mites, leeches, mosquitoes.
ECOLOGY 35

Fig 14.57 Diagrammatic representation of trophic levels in an ecosystem

 Organisms belonging to one trophic level have the same food habit. E.g., herbivory.
 However, each trophic level may have several resources like leaves, fleshy fruits, seeds, nectar, grasses, etc.
 A group of species belonging to a trophic level that exploit a common resource in a similar fashion is known as a guild. E.g.,
nectar-feeding birds, browsing animals, grazing animals.
 A trophic level is a functional level.
 Neither a guild nor a trophic level is occupied by a single species. A number of species may operate at it.
 Moreover, a single species may occupy more than one trophic level. A sparrow is a primary consumer if it feeds on seeds, fruits,
and peas. It is a secondary consumer if it feeds on insects and worms.
 Consumers that feed on all types of food are called omnivores. E.g., cockroach, crow. Human beings are also omnivores.
 Carnivorous (insectivorous) plants are both producers as well as carnivores though they digest small animals like saprotrophs.

9. Ecological Pyramids
 It is a graphical representation of ecological parameters, like biomass, energy, and the number of individuals present in various
trophic levels of a food chain. They were developed by Charles Elton. Hence, they are also called Eltonian pyramids.
 The base of each pyramid represents the producers or the first trophic level while the apex represents the tertiary or top-level
consumers. Quantity at each level is indicated by the length of the bar in the graph. Ecological pyramids are usually prepared
for three parameters: number of individuals, amount of biomass, and amount of energy.

9.1 Pyramid of Numbers

It is a graphical representation of the number of individuals per unit area of various trophic levels. Features of a pyramid of numbers
are as follows:
 In most cases, the pyramid of numbers is upright.
 The length of each bar is proportional to the number of individuals at that trophic level.
36 ECOSYSTEM

 The number of individuals is usually maximum at the producer level.

 Herbivores feeding on producers are less in number.
 Herbivores support fewer secondary consumers and so on.
 E.g., In a grassland ecosystem, a large number of grasses support a smaller number of herbivorous grasshoppers, which in turn
support fewer frogs, that are the prey of an even smaller number of snakes.

Fig 14.58 Pyramid of numbers in a grassland ecosystem. Only three top-carnivores

are supported in an ecosystem based on the production of nearly 6 million plants

 Similarly, in a pond ecosystem, a large number of phytoplankton support a smaller number of zooplankton, which in turn
support fewer small fishes, that are the prey of an even smaller number of large fishes.
 The large fishes are prey to an even smaller number of sharks (top consumers).

Fig 14.59 Pyramid of numbers in aquatic ecosystem

Variations in the Pyramid of Numbers

 The pyramid of numbers does not take into account the size of the individuals.
 A caterpillar, bird, rabbit, deer, elephant, whale, all are considered equal.
 Hence, a lot of variations are found in the pyramid of numbers: Inverted and spindle-shaped pyramids.
 Inverted Pyramid of Numbers: A single tree supports a number of herbivores or frugivorous birds. Each bird has a
number of ectoparasites and endoparasites.
ECOLOGY 37

Fig 14.60 Pyramid of Numbers: Inverted

 Spindle-shaped Pyramid of Numbers: A single tree supports a number of herbivorous birds. The birds are eaten by one or
two hawks of the area.

Fig 14.61 Pyramid of Numbers: Spindle-shaped

Differences between Upright Pyramid and Inverted Pyramid

Upright Pyramid Inverted Pyramid

The number or biomass of producers occupying the base is The number or biomass of producers is minimum and increases
maximum in an ecosystem. progressively with each trophic level.

The bar comprising producers is the largest and the apex The bar comprising producers is the smallest and the apex
comprising top consumers is the smallest. comprising top consumers is the largest.

The pyramid of energy is always upright. Pyramids of numbers and biomass may be inverted.

9.2 Pyramid of Biomass

The amount of living organic matter (expressed as weight) at any particular trophic level at a given time is called biomass or standing
crop. The pyramid of biomass is a graphical representation of biomass per unit area of different trophic levels.
 Only 10 to 20% of biomass is transferred from lower to higher trophic levels. The rest is consumed in providing energy for
giving heat, overcoming entropy, and performing various body activities.
 Maximum biomass occurs at the producer level. There is a progressive reduction of biomass found in herbivores, primary
carnivores, and so on.
38 ECOSYSTEM

Fig 14.62 Pyramid of biomass shows a sharp decrease in biomass at higher trophic levels

 The pyramid of biomass is usually upright for terrestrial ecosystems. E.g., tree and grassland ecosystems.
 Drawbacks of the pyramid of biomass:
 The biomass of a trophic level can be different in different periods of the year. For example, a deciduous tree has more
biomass in spring than autumn or winter.
 The rate of formation and accumulation of biomass is not taken into account.
 In aquatic ecosystems, the pyramid of biomass can be inverted or spindle-shaped.
 Inverted pyramid of Biomass:
 Biomass of phytoplanktons is lesser than that of zooplanktons. This is because the life span of zooplanktons is longer.
 The phytoplanktons multiply much faster but have a shorter life span. Therefore, a number of generations of phytoplanktons
can be consumed by a single generation of zooplanktons.
 The biomass of fish may still be larger because of their larger size and longer life span. Hence, a number of generations of
zooplanktons can be consumed by fishes.
 However, during transfer, only 10% of the biomass of one generation is passed on to the next trophic level.
 Sum total of biomass of benthic animals and brown algae exceeds the other producers and consumers in the
aquatic ecosystem.

Fig 14.63 Inverted pyramid of biomass- Small standing crop of

phytoplankton supports large standing crop of zooplankton

Fig 14.64 Aquatic Ecosystem

9.3 Pyramid of Energy

 It is a graphic representation of the amount of energy trapped per unit time and area in different trophic levels of a food chain
with producers forming the base and top carnivores at the tip.
 The energy content is expressed as kcal/m2/yr or KJ/m2/yr.
 Maximum energy is found at the producer level as they obtain energy directly from solar radiation.
 Only 10% of energy from producers accumulates into herbivores and so on as proposed by the 10% law of Lindeman.
 The pyramid of energy is always upright because when energy flows in a unidirectional manner from a particular trophic
level to the next trophic level, some energy is always lost as heat at each step.
 Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per
unit area.
 It is more accurate than a pyramid of biomass or pyramid of numbers.
ECOLOGY 39

Fig 14.65 An ideal pyramid of energy. Observe that primary producers convert only 1%
of the energy in the sunlight available to them into NPP.
Advantages:
 It provides information regarding the amount of energy required to support a trophic level in the ecosystem.
 It is based on productivity instead of biomass.
 It provides a comparative account among different ecosystems and different populations of the same ecosystem.
In most ecosystems, all the pyramids, of number, of energy, and biomass are upright, i.e., producers are more in number and biomass
than the herbivores, and herbivores are more in number and biomass than the carnivores. Also, energy at a lower trophic level is
always more than at a higher level.

9.4 Limitations of Ecological Pyramids

 It does not take into account the same species that can belong to two or more trophic levels. E.g., insectivorous plants.
 They are based on simple food chains, which almost never exist in nature.
 It does not accommodate a food web.
 Saprophytes, decomposers, microbes, and detrivores are not given any place in ecological pyramids, even though they play a
vital role in the ecosystem.

10. Ecological Succession

Fig 14.66 Ecological succession

 The gradual and fairly predictable change in the species composition of a given area is called ecological succession or
biotic succession.
 A series of biotic communities form at the same site over a period of time, one after the other, till a stable climax community
is reached. This climax community is well adapted to the climate of that region.
 Succession occurs because each community changes the environment of the area that is suitable for another community
than itself.
 Pioneer community: The first biotic community which develops in a bare area is called the pioneer community. It has very
little diversity. This stage takes the longest time to change the environment for the next community.
 Climax community: It is the stable, self-perpetuating, and final biotic community that develops at the end of biotic succession
that is in near equilibrium with the environment.
It has maximum diversity and niche specialization.
 Sere: The entire sequence of biotic succession from pioneer to climax community in a given area is called sere.
 Seral communities: The individual transitional communities that develop during succession are termed seral stages or
seral communities.

10.1 Changes During Biotic Succession

40 ECOSYSTEM

 Small short-lived plants (r-selection) to large long-lived plants (k-selection)

 Little diversity to a high degree of diversity
 Increase in biomass
 Increase in soil differentiation
 Increase in humus content of soil
 Aquatic or dry conditions to mesic conditions
 Unstable biotic community to stable community
 Simple food chains to complex food webs

10.2 Steps in a Biotic Succession

10.3 Type of Ecological Succession

Depending on the type of nudity in an area, succession is of two main types: Primary and Secondary.

10.3.1 Primary Biotic Succession

 It is a succession that occurs in a previously sterile or bare area.
 The establishment of a new biotic community is generally slow.
 Before a biotic community of diverse organisms can become established, there must be soil.
 Depending mostly on the climate, it takes natural processes several hundred to several thousand years to produce fertile soil on
bare rock.
 Examples of areas where primary biotic succession takes place are newly cooled lava, bare rock, newly created pond
or reservoir.
ECOLOGY 41

Fig 14.67 Primary succession

10.3.2 Secondary Biotic Succession

 Secondary biotic succession is a succession that occurs in an area that, somehow, lost all the living organisms that existed there.
 The reason for the destruction of the previous community may be flood, landslide, drought, forest fire, etc.
 Since some soil or sediment is present, succession is faster than primary succession.
 Underground parts, some seeds, remnant species, and invaders quickly form new communities as soon as conditions
become favorable.
42 ECOSYSTEM

Fig 14.68 Secondary Succession

Fig 14.69 Secondary Succession: Regrowth after Deforestation

Differences between Primary Succession and Secondary Succession

ECOLOGY 43

Based on the nature of the habitat – whether it is on very dry areas or it is water (or very wet areas) – the succession of
plants is called xerarch or hydrarch, respectively.
 Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions.
 Hydrarch succession takes place in wet areas and the successional series progress from hydric to mesic conditions.
 Hence, both hydrarch and xerarch succession lead to medium water conditions (mesic) – neither too dry (xeric) nor too
wet (hydric).

10.3.3 Xerarch Succession

 It is a sequence of successional stages that occur in xeric or dry environments like bare rocks.
 Stages in xerarch succession occurring on a bare rock is called lithosere. Because the bare rock is deficient in water, this lithosere
is also called xerosere.
 The bare rock habitat is extremely hostile to living organisms.
 The first pioneers of such a habitat are usually lichens in the temperate region and blue-green algae in tropical regions.
Stage 1- Lichen Stage
 The wet rock surface is occupied by pioneer crustose lichens that are able to secrete acids to dissolve rock, bringing about
weathering of rocks and soil formation.
 Later on, the crustose lichens are replaced by foliose lichens.

Fig 14.70 Lichen stage

Stage 2- Moss Stage
 Foliose lichens make conditions more suitable for hardy mosses. They shade the lichens and finally replace them.
 Mosses have a gregarious habit and their rhizoids penetrate deeper into the rocks.
 Mosses accumulate more soil and organic matter.
44 ECOSYSTEM

Fig 14.71 Moss stage

Stage 3- Annual Grass Stage
 More soil added by mosses makes substratum suitable for germination of seeds of annual grasses. E.g., Poa, Justicia,
Tridax, etc.
 The grasses grow, their roots penetrate deeper and cause further fragmentation. This increases the moisture and soil.
 Long-lived annual grasses grow rapidly.

Fig 14.72 Annual grass stage

Stage 4- Perennial Grass Stage
 Increased moisture and soil in the crevices invite perennial grasses.
 The perennial grasses have runners and rhizomes which rapidly spread the grasses. E.g, Themeda, Cymbopogon.
 Shade, moisture, soil, perennial vegetation, and seeds, invite small animals.

Fig 14.73 Perennial grass stage

Stage 5- Shrub stage
 Seeds and rhizomes of xerophytic shrubs invade the area. E.g., Zizyphus, Capparis.
 The roots of shrubs penetrate deeper, causing further cracks in the rocky substratum and increasing soil formation.
 Shrubs shade the area and enhance its moisture which invites trees and animals.
ECOLOGY 45

Fig 14.74 Shrub stage

Stage 6- Climax Community

 Hardy and light-demanding trees replace shrubs.
 The type of climax community depends on climate. So, it is also called the climatic climax community.
 In a moist tropical area, the climax community is rainforest; in temperate areas, it is deciduous forest.

Fig 14.75 Climax community

Fig 14.76 Xerarch succession

10.3.4 Hydrarch Succession
 Biotic succession occurring in aquatic environments is called hydrarch succession.
 The series of biotic communities that develop one after the other in a newly formed pond or lake is called hydrosere.
 There are different seral stages in hydrosere.
46 ECOSYSTEM

Stage 1- Phytoplankton Stage

 It is the pioneer stage of hydrosere.
 Spores of this stage reach into the water through wind or animals.
 Phytoplanktons (e.g., diatoms, green algae, etc.) appear first and multiply rapidly.
 A balance is created by the appearance of zooplanktons that feed on the phytoplanktons.
 Death and decomposition of plankton produce organic matter and make substratum suitable for the next stage.

Fig 14.77 Phytoplankton stage

Stage 2- Submerged Plant Stage
 The bottom is lined by soft mud having organic matter which is favorable for the growth of submerged plants like
Hydrilla, Vallisneria.
 They are rooted in the mud and have dense growth.
 As a result, sand and silt get deposited around the plants and the bottom layer rises slowly.
 The older plants get buried and make the substratum suitable for the next stage.

Fig 14.78 Submerged Plant Stage

Stage 3- Submerged Free-Floating Plant Stage

 The floating-leaved anchored plants appear where water is shallow. E.g., Nymphaea, Nelumbo.
 These plants make water rich in mineral and organic matter.
 It becomes suitable for the growth of free-floating plants. E.g., Lemna, Azolla.
 The rapid growth of floating plants builds up the bottom and water becomes shallow on the periphery.
ECOLOGY 47

Fig 14.79 Submerged Free-Floating Plant Stage

Stage 4- Reed Swamp Stage
 Amphibious plants grow where the water body becomes shallow. E.g., Phragmites, Typha.
 The plants of the swamp stage transpire huge quantities of water.
 They also produce abundant organic matter.

Fig 14.80 Reed Swamp Stage

Stage 5- Sedge or Marsh Meadow Stage
 The shores built up by the reed swamp stage are invaded by sedges like Cyperus.
 These plants transpire rapidly and add abundant humus.
 Therefore, soil is build up to invite the next stage.

Fig 14.81 Marsh Meadow Stage

Stage 6- Woodland or Scrub Stage
 The periphery of the sedge meadow stage is invaded by shrubby plants. E.g., Cornus.
 The shrubs shade away the sedges and invite trees capable of bearing bright light and waterlogging. E.g., Populus, Salix.
 The plants lower the water table by transpiration. They also build up more soil.
48 ECOSYSTEM

Fig 14.82 Woodland or Scrub Stage

Stage 7- Climax Forest
 New trees invade the area. They have shade-loving seedlings and grow to greater heights.
 The climax forest depends on the climate.

Fig 14.83 Climax Forest

ECOLOGY 49

Fig 14.84 Hydrarch succession

Differences between Xerarch Succession and Hydrarch Succession

10.4 Importance of Biotic Succession

 Maintenance of grasslands: It tells us about how a biotic seral stage like grasses and herbs of a pasture can be maintained by
not allowing the biotic succession to proceed further by interfering with grazing or forest fires.
 Care of dams: Dams are protected by preventing siltation so that biotic succession does not occur.
50 ECOSYSTEM

 Maintenance of monoculture forests: Monoculture forests are artificial forests. They are maintained so that they are not
replaced by the next species. E.g., Teak forest.

Fig 14.85 Teak Forest

 Reforestation and afforestation: Biotic succession provides information about the soil substratum of the area so that particular
species can be planted.

11. Nutrient Cycling

 Nutrients are inorganic substances representing the usable form of essential elements.
 They become part of biotic components and are called biogenetic nutrients. Since they are obtained from the earth, they are
also called biogeochemicals.
 The amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time, is referred
to as the standing state.

Fig 14.86 Nutrients

 The repeated circulation of nutrients between biotic and abiotic components of the ecosystem is called nutrient cycling.
 Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo: rocks, air, water).
 Nutrients are never lost from the ecosystems, rather they are recycled time and again indefinitely.
 They are the storehouse of biogenetic materials. They are of two types:
 Cycling or Nutrient Pool: It is the pool of biogenetic nutrients that is used again and again by producers and continuously
replenished by the activity of decomposition.
 Reservoir Pool: It is a storehouse of nutrients that are not readily available to producers but are being slowly transferred
to the cycling pool. E.g., phosphate in rocks, carbon from carbonate rocks, etc.
ECOLOGY 51

11.1 Types of Biogeochemical Cycles

Differences between Gaseous cycle and Sedimentary cycle

 Environmental factors like soil, moisture, pH, temperature, etc., regulate the rate of release of nutrients into the atmosphere.
 The function of the reservoir is to meet with the deficit which occurs due to an imbalance in the rate of influx and efflux.
11.1.1 Carbon Cycle
 Importance of Carbon- Carbon is the component of all organic substances. It constitutes 49% of the dry weight of organisms,
therefore, next only to water in abundance.
 The atmosphere only contains about 1% of the total global carbon.
 Oceanic reservoirs regulate the amount of carbon dioxide in the atmosphere.

Fig 14.57 Sources of Carbon

52 ECOSYSTEM

Carbon content and its recycling

 Carbon cycling occurs through the atmosphere, ocean, and through living and dead organisms.
 The cycling pool is the atmosphere and hydrosphere, the reservoir pool is the lithosphere.
 Carbon in the lithosphere is available only when it is burnt or changed chemically.
 Carbon present in the atmosphere and hydrosphere is picked up by producers and changed into organic compounds in the
process of photosynthesis. Oxygen is released as a by-product.

Fig 14.58 Carbon fixation by photosynthesis

 According to one estimate, 4 × 1013 kg of carbon is fixed in the biosphere through photosynthesis annually.
 Carbon fixed by producers enters the food chain and is passed to herbivores, carnivores, and decomposers.

Fig 14.59 Movement of carbon in the food chain

 The carbon in the atmosphere and hydrosphere is replenished by five methods:

 Respiration of organisms
 Decomposition of organic matter
 Burning of wood and fossil fuels
 Weathering of carbonate-containing rocks
 Volcanic eruptions, hot springs, and forest fires
 Some amount of the fixed carbon is lost to sediments and removed from circulation. It is added to the lithosphere by hard
carbonaceous shells, skeletons of animals, fossilization, formation, and sedimentation of carbonates.
ECOLOGY 53

Fig 14.60 Removal of fixed carbon from circulation

Fig 14.61 Carbon cycle

54 ECOSYSTEM

 Human activities have significantly influenced the carbon cycle.

 Rapid deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release
of carbon dioxide into the atmosphere.

Fig 14.62 Human activities increase the rate of release of carbon dioxide into the atmosphere

11.1.2 Phosphorus Cycle

 It is a sedimentary cycle where phosphorus circulates between biotic and abiotic components of the ecosystem.
 Importance of Phosphorus:
 It is a major constituent of biological membranes (phospholipids), nucleic acids, and cellular energy transfer
systems (ATP).
 Many animals also need large quantities of this element to make shells, bones, and teeth.

Fig 14.63 Importance of Phosphorus

 Main sources: The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates. Its cycling
pool is soil for terrestrial ecosystems and water for aquatic ecosystems.
 When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of
the plants.
 Phosphate in soil may occur in an insoluble form. It is dissolved by chemicals secreted by microorganisms and plant roots.
 The dissolved phosphate is absorbed by plants and changed to organic form.
 Humans add phosphate fertilizers to the soil to increase its availability.
 Herbivores and other animals obtain this element from plants.
 The waste products and the dead organisms are decomposed by phosphate-solubilizing bacteria releasing phosphorus.
ECOLOGY 55

 Unlike the carbon cycle, there is no respiratory release of phosphorus into the atmosphere.
 Inside soil, some phosphorus is lost through leaching.
 A sufficient amount of phosphorus combines with iron, aluminum, or calcium and becomes insoluble.
 It settles down at the bottom of lakes or oceans as sediments. Bones and teeth may also remain undegraded.
 Such phosphorus becomes part of the lithosphere. It is released only when rocks are exposed and weathered.

Fig 14.64 Phosphorus cycle

Fig 14.65 A simplified model of phosphorus cycling in a terrestrial ecosystem

56 ECOSYSTEM

Differences between Carbon Cycle and Phosphorus Cycle

12. Population Interactions

 No natural habitat on earth is inhabited just by a single species.
 For any species, the minimal requirement is one more species on which it can feed.
 Even a plant species, which makes its own food, cannot survive alone.
 It needs soil microbes to break down the organic matter in soil and return the inorganic nutrients for absorption.
 Plants need an animal agent for pollination.
 Animals, plants, and microbes do not and cannot live in isolation but interact in various ways to form a biological community.
 Different species are dependent on each other for survival and so they interact.
 Different populations interact differently.
 Interspecific interactions arise from the interaction of populations of two different species.
 They could be beneficial, detrimental, or neutral (neither harm nor benefit) to one of the species or both.
 A ‘+’ sign for beneficial interaction, a ‘-’ sign for detrimental, and ‘0’ for neutral interaction are usually assigned.
 Based on the nature of interactions, we can classify them into the following categories:

NOTE:
ECOLOGY 57

Predation, parasitism, and commensalism share a common characteristic– the interacting species live closely together.

12.1 Mutualism (+ , +)
 Mutualism is an interaction between two organisms of different species where both partners benefit and help each other in
survival.
 Examples- lichens, mycorrhiza, cellulose digestion in animals, seed dispersal, etc.

12.1.1 Lichens
 An intimate mutualistic relationship between a fungus (provides water, minerals, and shelter) and photosynthesizing algae
(provides food) or cyanobacteria.
12.1.2 Mycorrhizae
 Associations between fungi and the roots of higher plants.
 The fungi help the plant in absorption of essential nutrients from the soil while the plant, in turn, provides the fungi with
energy-yielding carbohydrates.

Lichen (left) and Mycorrhizae (right)

12.1.3 Termites and cellulose digesting protozoa
 Termites feed on the dead wood. They depend on cellulose digesting flagellates like Trichonympha campanula to provide
the enzymes to digest wood.
 These protozoa would die outside of the termite, and the termite would starve if it did not have the protozoa to aid in
digestion.
58 ECOSYSTEM

Fig 13.91: Termites

12.1.4 Plant-animal relationships
 Plants need the help of animals for pollinating their flowers (entomophilous flowers) and dispersing their seeds.
 Plants offer rewards or fees in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersers.

Pollen and nectar for pollinators (left) and Nutritious fruits for seed dispersers (right)

 This mutually beneficial system should also be safeguarded against ‘cheaters’, for example, some animals try to steal nectar
without helping in pollination.
 Plant-animal interactions often involve co-evolution of the mutualists, i.e., the evolution of the flower and its pollinator species
are tightly linked with one another.
Fig and wasps
 In many species of fig trees, there is a tight one-to-one relationship with the pollinator species of wasp.

Wasps and fig flower

 It means that a given fig species can be pollinated only by its ‘partner’ wasp species and no other species.
 The female wasp uses the fruit not only as an oviposition (egg-laying) site but uses the developing seeds within the fruit for
nourishing its larvae.
 The wasp pollinates the fig inflorescence while searching for suitable egg-laying sites.
 In return for the favor of pollination, the fig offers the wasp some of its developing seeds, as food for the developing
wasp larvae.
ECOLOGY 59

Wasps pollinating fig inflorescence

Orchid and bee
 Orchids show a bewildering diversity of floral patterns.
 Many have evolved to attract the right pollinating insect (bees and bumblebees) and ensure guaranteed pollination by it.
 Not all orchids offer rewards.
 The Mediterranean orchid Ophrys employs ‘sexual deceit’ to get pollination done by a species of bee.
 One petal of its flower bears an uncanny resemblance to the female of the bee in size, color and markings.
 The male bee is attracted to what it perceives as a female, ‘pseudo copulates’ with the flower, and is dusted with pollen from
the flower.
 When this same bee ‘pseudo copulates’ with another flower, it transfers pollen to it and thus, pollinates the flower.
 This is how co-evolution operates.
 If the female bee’s color patterns change even slightly for any reason during evolution, pollination success will be reduced,
unless the orchid flower co-evolves to maintain the resemblance of its petal to the female bee.
60 ECOSYSTEM

Ophrys flower with bee

12.2 Competition (- , -)
 It is a rivalry between two or more organisms for obtaining the same resources.
 It can be of two types:

Types of Competition
 Darwin was convinced that interspecific competition is a potent force in organic evolution in the struggle for existence and
survival of the fittest.
 It is generally believed that competition occurs when closely related species compete for the same resources that are limiting,
but this is not entirely true.
 Firstly, totally unrelated species also compete for the same resources (Interspecific competition).
 For instance, in some shallow South American lakes visiting flamingoes and resident fishes compete for their common food,
the zooplankton in the lake.
 Secondly, resources need not be limiting for competition to occur.
 In interference competition, the feeding efficiency of one species might be reduced due to the interfering and inhibitory
presence of the other species, even if resources (food and space) are abundant.
ECOLOGY 61

 Therefore, competition is best defined as a process in which the fitness of one species (measured in terms of its ‘r’, the intrinsic
rate of increase) is significantly lower in the presence of another species.
12.2.1 Principle of competitive exclusion
 Gause found that when two species of Paramecium (P. aurelia and P. caudatum) are grown together, one is eliminated.
 Two species competing for the same resources cannot co-exist.
 A competitively inferior one will be eliminated eventually if resources are limited.

Competitive exclusion in Paramecium

 The Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, due to
the greater browsing efficiency of the goats.

12.3 Predation (+, -)

 Predation is a biological interaction where one organism─ the predator, kills and eats another organism─ its prey.
62 ECOSYSTEM

Predation in Nature

 With the terms predator and prey, usually animals come to mind, but a sparrow eating any seed is also a predator.
 Animals eating plants are categorized separately as herbivores, however, in a broad ecological context, they are not very
different from predators.
12.3.1 Importance of Predation
 Transfer of energy
 Predation is nature’s way of transferring to higher trophic levels the energy fixed by plants.
 Predators act as ‘conduits’ for energy transfer across different trophic levels.

Transfer of energy from one trophic level to the next

 Predators keep prey populations under control.

 For example- the prickly pear cactus, introduced in Australia caused havoc by spreading rapidly because its natural predator
was not present.
 It was brought under control after introducing a predator (a moth) from its natural habitat.
Prey- Cactus (left) and Predator- Larvae of moth feeding on cactus (right)

Predator-prey relationship
ECOLOGY 63

 Maintaining species diversity

 It is done by
 reducing interspecific competition in a community,
 reducing the intensity of competition among competing prey species.
 For example- In the rocky intertidal communities of the American Pacific Coast, the starfish Pisaster is an
important predator.
 In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of
invertebrates became extinct within a year, because of interspecific competition.

Pisaster
Why are predators ‘prudent’?
 If a predator is too efficient and over-exploits its prey, then the prey might become extinct.
 Predators will also become extinct for lack of food. That is why predators in nature are ‘prudent’.
 Prey species have evolved defense mechanisms to lessen the impact of predation.
12.3.2 Defense Against Predation in Animals
 Some species of insects, and other organisms (e.g., frog, grasshopper, chameleons) are cryptically-colored (camouflaged) to
avoid being detected by the predator.

Chameleon (left) and Frog (right)

 The Monarch butterfly is highly distasteful (bitter) to its predator (bird) because of a special chemical present in its body.
 The butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed.

Monarch butterfly (left) and Caterpillars feeding on weed (right)

64 ECOSYSTEM

 Some animals are poisonous and therefore avoided by the predators, e.g., Snakes.

12.3.3 Defense Against Predation in Plants

 For plants, herbivores are the predators.
 Nearly 25 percent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants).
 The problem is particularly severe for plants because, unlike animals, they cannot run away from their predators.
 Plants, therefore, have evolved an astonishing variety of morphological and chemical defenses against herbivores.
Morphological means of defense
 Thorns (Acacia, Bougainvillea) and spines (Cactus) are the most common.

Thorns (left) and Spines (right)

Chemical means of defense

 Many plants produce and store chemicals that make the herbivore sick when they are eaten.
 Such chemicals inhibit feeding or digestion, disrupt herbivores’ reproduction or even kill it.
 A wide variety of chemical substances extracted from plants on a commercial scale (nicotine, caffeine, quinine, strychnine,
opium, etc.) are actually produced by them as defenses against grazers and browsers.
 The weed Calotropis growing in abandoned fields produce highly poisonous cardiac glycosides and that is why no cattle or
goats browse on this plant.

12.4 Parasitism (+ , -)
 It is a relationship between two organisms, in which one organism─ the parasite, thrives at the cost of the other─ the host.

Worm (parasite) and Human intestine (Host)

 Many parasites have evolved to be host-specific (they can parasitize only a single species of the host) in such a way that both
host and the parasite tend to co-evolve.
 If the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to counteract
and neutralize them in order to be successful with the same host species.
Adaptations of a parasite
 Loss of unnecessary sense organs
ECOLOGY 65

 Presence of adhesive organs like hooks or suckers to cling on to the host

 Loss of digestive system
 High reproductive capacity
 The life cycle of parasites is often complex, involving one or two intermediate hosts or vectors to facilitate the parasitization of
its primary host.
 The human liver fluke (a trematode parasite) depends on two intermediate hosts (a snail and a fish) to complete its life cycle.

Life cycle of Human liver fluke

 The malarial parasite needs a vector (mosquito) to spread to other hosts.
 The majority of the parasites harm the host; they may reduce the survival, growth, and reproduction of the host and reduce its
population density.
 They might render the host more vulnerable to predation by making it physically weak.
Types of Parasites
66 ECOSYSTEM

Ectoparasite- Lice on hairs (left) and Cuscuta on hedge plants (right)

Endoparasite
Different types of Parasites

Brood Parasitism
 Brood parasitism is when a bird lays its eggs in the nest of another bird.
 The host bird (the owner of the nest) is then responsible for raising and feeding the parasite bird chick, e.g., Cuckoo in the
crow's nest.
 During the course of evolution, the eggs of the parasitic bird have evolved to resemble the host’s egg in size and color to reduce
the chances of the host bird detecting the foreign eggs and ejecting them from the nest.

Cuckoo eggs in crow’s nest (left), Cuckoo and Crow (right)

12.5 Commensalism (+, 0)

 It is the interaction in which one species benefits and the other is neither harmed nor benefited.
 Examples-
 Barnacles grow on the back of a whale benefit (shelter) while the whale does not derive any apparent benefit.
ECOLOGY 67

Barnacles on the back of a whale (left) and Barnacles (right)

 An orchid growing as an epiphyte on a mango branch. Epiphytes obtain water from air through epiphytic roots and grow
on other plants for space.
 The cattle egret and grazing cattle are commonly seen in close association in farmed rural areas. The egrets always forage
close to the grazing cattle because the movement of cattle stirs up vegetation and flushes out the insects that otherwise
might be difficult for the egrets to find and catch.

Orchid on mango tree (left), Cattle and egrets (right)

 Clownfish and sea anemones- The fish gets protection from predators which stay away from the stinging tentacles of
anemones. The anemone does not appear to derive any benefit by hosting the clownfish.

Clownfish and Sea anemone

12.6 Amensalism (- , 0)
 Amensalism is an interaction between two individuals of different species in which an organism does not allow another
organism to grow or live near it.
 Inhibition is achieved through the secretion of chemicals called allochemics.
 For the commercial production of antibiotics, these types of interactions are very useful.
68 ECOSYSTEM

 Examples-
 Penicillium does not allow the growth of Staphylococcus bacteria.
 Convolvulus arvensis is a common weed that inhibits the germination and growth of wheat.

Penicillium inhibiting Staphylococcus (left) and Convolvulus growing in wheat field (right)

 Black walnut produces a chemical named juglone. It is toxic to apples, tomatoes, and Alfalfa. The phenomenon of inhibiting
the growth of other organisms through the secretion of toxic chemicals is known as allelopathy.
ECOLOGY 69

EXERCISE (Basic Exercise) (d) The absence of soil organisms

5. Which of the following would appear as
1. During ecological succession
the pioneer organisms on bare rocks?
(a) the gradual and predictable change
(a) Liverworts
in species composition occurs in a given
(b) Mosses
area
(c) Green algae
(b) the establishment of a new biotic
(d) Lichens
community is very fast in its primary
6. The term ecosystem was coined by
phase
(a) AG Tansley
(c) the numbers and types of animals
(b) E Haeckel
remain constant
(c) E Warming
(d) the changes lead to a community
(d) EP Odum
that is in near equilibrium with the
7. In which of the following both pairs
environment and is called pioneer
have the correct combination?
community
(a Gaseous Carbon
2. Which ecosystem has the maximum
) nutrient and
biomass?
cycle nitrogen
(a) Forest ecosystem
Sedimentar Sulphur
(b) Grassland ecosystem
y nutrient and
(c) Pond ecosystem
cycle phosphoru
(d) Lake ecosystem
s
3. Th primary producers of the deep-sea
(b Gaseous Carbon
hydrothermal vent ecosystem are
) nutrient and
(a) green algae
cycle Sulphur
(b) chemosynthetic bacteria
Sedimentar Nitrogen
(c) blue-green algae
y nutrient and
(d) coral reefs
cycle phosphoru
4. Which one of the following is a
s
characteristic feature of cropland
(c Gaseous Nitrogen
ecosystem?
) nutrient and
(a) Least genetic diversity
cycle Sulphur
(b) The absence of weeds
Sedimentar Carbon
(c) Ecological succession
70 ECOSYSTEM

y nutrient and A. Earthworm 1. Pioneer

cycle phosphoru species
s B. Succession 2. Detritivore
(d Gaseous Sulphur C. Ecosystem 3. Natality
) nutrient and service
cycle phosphoru D. Population 4. Pollination
Sedimentar s Carbon growth
y nutrient and (a) A -1; B -2; C -3; D -4
cycle nitrogen (b) A -4; B -1; C -3; D -2
(c) A -3; B -2; C -4; D -1
8. Vertical distribution of different species (d) A -2; B -1; C -4; D -3
occupying different levels in a biotic 12. Secondary productivity is rate of
community is known as formation of new organic matter by
(a) divergence (a) producer
(b) stratification (b) parasite
(c) zonation (c) consumer
(d) pyramid (d) decomposer
9. Secondary succession takes place on/in 13. Which one of the following processes
(a) bara rock during decomposition is correctly
(b) degraded forest described?
(c) newly created pond (a) Fragmentation-Carried out by
(d) newly cooled lava organisms such as earthworm
10. The mass of living material at a tropic (b) Humification-Leads to the
level at a particular time is called accumulation of a dark coloured
(a) gross primary productivity substance humus, which undergoes
(b) standing state microbial action at a very fast rate
(c) net primary productivity (c) Catabolism-Last step in the
(d) standing crop decomposition under fully anaerobic
11. Match the following and select the condition
correct option. (d) Leaching-Water soluble inorganic
Column I Column II nutrients rise to the top layers of soil.
ECOLOGY 71

14. Which one of the following is not a (a) Energy flow

gaseous biogeochemical cycle in (b) Decomposition
ecosystem? (c) Productivity
(a) Oxygen cycle (d) Stratification
(b) Phosphorus cycle 18. The upright pyramid of number is
(c) Nitrogen cycle absent in
(d) Carbon cycle (a) pond
15. Identify the possible link A in the (b) forest
following food chain (c) lake
Green plant → Insect → Frog → A → (d) grassland
Eagle 19. Which one of the following statements
(a) rabbit is correct for secondary succession?
(b) wolf (a) It occurs on a deforested site
(c) cobra (b) It follows primary succession
(d) parrot (c) It is similar to primary succession
16. Given below is an imaginary pyramid of except that it has a relatively fast pace
numbers. What could be one of the (d) It begins on a bare rock
possibilities about certain organisms at 20. Which one of the following statements
some of the different levels? for pyramid of energy is incorrect,
whereas the remaining three are
correct?
(a) It shows energy content of different
trophic level organisms
(b) It is inverted in shape
(a) Level PC is insects and level SC is
(c) It is upright in shape
small insectivorous birds.
(d) Its base is broad
(b) Level PP is phytoplanktons in sea
21. Mass of living matter at a trophic level
and whale on top level TC
in an area at any time is called
(c) level one PP is pipal trees and the
(a) Detritus
level SC is sheep
(b) Humus
(d) Level PC is rats and level SC is cats
(c) Standing state
17. Which one of the following is not a
(d) Standing crop
functional unit of an ecosystem?
72 ECOSYSTEM

22. Of the total incident solar radiation the 26. Which one of the following types of
proportion of PAR is organisms occupy more than one tropic
(a) about 60% level in a pond ecosystem?
(b) less than 50% (a) Phytoplankton
(c) more than 80% (b) Fish
(d) about 70% (c) Zooplankton
23. The biomass available for consumption (d) Frog
by the herbivores and the decomposers 27. About 70% of total global carbon is
is called found in
(a) net primary productivity (a) grasslands
(b) secondary productivity (b) agro-ecosystems
(c) standing crop (c) oceans
(d) gross primary productivity (d) forests
24. Which one of the following is one of the 28. The slow rate of decomposition of
characteristics of a biological fallen logs in nature is due to their
community? (a) low moisture content
(a) Stratification (b) poor nitrogen content
(b) Natality (c) anaerobic environment around them
(c) Mortality (d) low cellulose content
(d) Sex-ratio 29. Consider the following statements
25. The correct sequence of plants in a concerning food chains
hydrosere is (i) Removal of 80% tigers from an area
(a) Oak → Lantana → Scirpus → resulted in greatly increased growth of
Pistia → Hydrilla → Volvox vegetation
(b) Volvox → Hydrilla → Pistia → (ii) Removal of most of the carnivores
Scirpus → Lantana → Oak resulted in an increased population of
(c) Pistia → Volvox → Scirpus → deers
Hydrilla → Oak → Lantana (iii) The length of food chains is
(d) Oak → Lantana → Volvox → generally limited to 3-4 trophic levels
Hydrilla → Pistia → Scirpus due to energy loss
(iv) The length of food chains may vary
from 2 to 8 trophic levels
ECOLOGY 73

Which two of the above statements are 34. The bacteria which attack dead animals
correct? are
(a) ii and iii (a) first link of the food chain and are
(b) iii and iv known as primary producers.
(c) i and iv (b) Second link of the food chain and
(d) i and ii are herbivorous
30. Which of the following ecosystem types (c) third link of the food chain and are
has the highest annual net primary tertiary consumers
productivity ? (d) the end of food chain and are
(a) Tropical rain forest decomposers.
(b) Tropical deciduous forest 35. Animals take phosphorus from
(c) Temperate evergeen forest (a) water
(d) Temperate deciduous forest (b) plants
31. Which one of the following is not used (c) rock
for construction of ecological (d) soil.
pyramids? 36. Most animals that live in deep oceanic
(a) Dry weight waters are
(b) Number of individuals (a) Tertiary consumers
(c) Rate of energy flow (b) Detritivores
(d) Fresh weight (c) Primary consumers
32. Mr. X is eating curd/yoghurt. For this (d) Secondary consumers
food intake in a food chain he should be 37. Energy flow in an ecosystem is
considered as occupying (a) unidirectional
(a) first trophic level (b) bidirectional
(b) second trophic level (c) multi-directional
(c) third trophic level (d) All the these
(d) fourth trophic level. 38. In a stable ecosystem, which of the
33. What is PAR range? following limits the number of trophic
(a) 200 nm - 800 nm levels?
(b) 400 nm - 700 nm (a) Biomass
(c) 350 nm - 550 nm (b) The number of nutrients
(d) 600 nm - 100 nm (c) Availability of nutrients
74 ECOSYSTEM

(d) Presence of contaminants that (c) secondary productivity

increase in concentration along the food (d) net productivity
chain 43. If 20 J of energy is trapped at producer
39. The amount of nutrients, such as level, then how much energy will be
carbon, nitrogen, phosphorus, calcium, available to peacock as food in the
etc. present in the soil at any given time, following chain? Plant → mice →
is referred to as the snake → peacock
(a) Nutrient status of soil (a) 0.02 J
(b) Standing state (b) 0.002 J
(c) Standing crop (c) 0.2 J
(d) Mineral state. (d) 0.0002 J
40. What type of ecological pyramid would 44. Pheretima and its close relatives derive
be obtained with the following data? nourishment from
Secondary consumer: 120 g (a) Sugarcane roots
Primary consumer: 60 g (b) Decaying fallen leaves and soil
Primary producer: 10 g organic matter
(a) Inverted pyramid of biomass (c) Soil insects
(b) Pyramid of energy (d) Small pieces of fresh fallen leaves of
(c) Upright pyramid of numbers maize
(d) Upright pyramid of biomass 45. Which one of the following statements
41. Presence of plants arranged into well- is correct for secondary succession?
defined vertical layers depending on (a) It occurs on a deforested site
their height can be seen best in: (b) It follows primary succession
(a) Tropical Rain Forest (c) It is similar to primary succession
(b) Grassland except that it has a relatively slow pace
(c) Temperate Forest (d) All of the above
(d) Tropical Savannah 46. Which of the following ecological
42. In an ecosystem the rate of production pyramids is generally inverted?
of organic matter during photosynthesis (a) Pyramid of biomass in a sea
is termed as (b) Pyramid of numbers in grassland
(a) net primary productivity (c) Pyramid of energy
(b) gross primary productivity (d) Pyramid of biomass in a forest
ECOLOGY 75

47. In relation to Gross primary (b) (a) – (iv); (b) - (iii); (c) - (ii); (d) –
productivity and Net primary (i)
productivity of an ecosystem, which (c) (a) – (i); (b) - (ii); (c) - (iii); (d) –
one of the following statements is (iv)
correct? (d) (a) – (ii); (b) - (iii); (c) - (iv); (d) –
(a) Gross primary productivity is (i)
always more than Net primary 49. Which of the following statements is
productivity. incorrect?
(b) Gross primary productivity and Net (a) Biomass decreases from first to
primary productivity are one and same. fourth trophic level
(c) There is no relationship between (b) Energy content gradually increases
Gross primary productivity and Net from first to fourth trophic level
primary productivity. (c) Number of individuals decreases
(d) Gross primary productivity is from first trophic level to fourth trophic
always less than net primary level
productivity (d) Energy content gradually decreases
48. Match the trophic levels with their from first to fourth trophic level
correct species examples in the green 50. Which of the following statements is
land ecosystem incorrect regarding the phosphorus
cycle?
(a) Fourth (i) Cow (a) Phosphates are the major form of
trophic level phosphorus reservoir
(b) Second (ii) Vulture (b) Phosphorus solubilizing bacteria
trophic level facilitate the release of phosphorus from
(c) First trophic (iii) Rabbit organic remains
level (c) There is the appreciable respiratory
(d) Third (iv) Grass release of phosphorus into the
trophic level atmosphere
Select the correct option: (d) It is a sedimentary cycle
(a) (a) – (iii); (b) - (ii); (c) - (i); (d) – 51. The rate of decomposition is faster in
(iv) the ecosystem due to the following
factors EXCEPT:
76 ECOSYSTEM

(a) Detritus rich in sugars (b) B

(b) Warm and moist environment (c) C
(c) Presence of aerobic soil microbes (d) D
(d) Detritus richer in lignin and chitin 54. In the equation GPP-R = NPP
52. Identify the likely organisms (a), (b), (c) represents:
and (d) in the food web shown below: (a) Environment factor
(b) Respiration losses
(c) Radiant energy
(d) Retardation factor
55. Which of the following statements is
not correct?
(a) Pyramid of energy is always upright.
(b) Pyramid of numbers in a grassland
(a) (a) – dog; (b) - squirrel; (c) - bat;
ecosystem is upright.
(d) – Dear
(c) Pyramid of biomass in sea is
(b) (a) – Rat; (b) - dog; (c) - Tortoise;
generally inverted.
(d) – crow
(d) Pyramid of biomass in sea is
(c) (a) – squirrel; (b) - cat; (c) - rat; (d)
generally upright.
– Pigon
56. Given below are two statements:
(d) (a) – Dear; (b) - Rabbit; (c) - frog;
Statement I: Decomposition is a
(d) – Rat
process in which the detritus is
53. Which of the following representations
degraded into simpler substances by
shows the pyramid of numbers in a
microbes.
forest ecosystem -
Statement II: Decomposition is faster if
the detritus is rich in lignin and chitin.
In the light of the above statements,
choose the correct answer from the
options given below:
(a) Statement I is correct incorrect but
statement II is correct
(b) Both statement I and II are correct

(a) A
ECOLOGY 77

(c) Both statement I and statement II are (a) Low temperature inhibits
incorrect decomposition
(d) Statement I is correct but statement (b) Warm and moist environment
II is incorrect favours the process
57. Which one of the following will (c) The process is anaerobic
accelerate phosphorus cycle? (d) It is slower if detritus is rich in
(a) Rain fall and storms proteins and carbohydrates
(b) Burning of fossil fuels (e) Detritus is degraded into simpler
(c) Volcanic activity inorganic substance by fungal
(d) Weathering of rocks and bacterial enzymes
58. Detritivores breakdown detritus into Choose the correct answer from the
smaller particles. This process is called: options given below:
(a) Decomposition (a) (b) and (c) only
(b) Catabolism (b) (c) (a) and (d) only
(c) Fragmentation (c) (c) and (d) only
(d) Humification (d) (c) (d) and (e) only
59. Identify the correct set of statements 61. Given below are two statements:
with regard to properties of humus Statement -I: Pyramid of energy is
(a) Highly resistant to microbial action always upright and is the most efficient
(b) Dark-colored amorphous substance Statement-II: Pyramid of biomass in sea
(c) End product of detritus food chain is generally inverted
(d) Reservoir of nutrients In the light of the above statements,
(e) Undergoes decomposition very fast choose the most appropriate answer
Choose the correct answer fro the from the options given below:
options given below: (a) Statements-I is correct but
(a) (a), (b) and (d) only statement-II is incorrect
(b) (a) (b) and (e) only (b) Statements-I is incorrect but
(c) (a) and (b) only statement-II is correct
(d) (b), (c) and (a) (c) Both statement-I and statements-II
60. Which of the following are not correct are correct
regarding decomposition of wastes ? (d) Both statement-I and statement-II
are incorrect
78 ECOSYSTEM

62. When certain exotic species are (d) Competitive Inclusion

introduced into a geographical area they 65. Which of the following is not an
become invasive mainly because: ectoparasite?
(a) The invaded land has unlimited (a) Lice on humans
resources for the introduced species (b) Copepods on marine fishes
(b) The invaded land does not have its (c) Mistletoe on other plants
natural predator (d) Female Anopheles on humans
(c) The population of the introduced 66. To get pollinated by a bee, the
species in the invaded land is very low Mediterranean Orchid, Ophrys,
(d) Introduced species do not face any employs:
competition in the introduced land (a) Sexual deceit
63. In a field experiment, when all Pisaster (b) Pseudo-copulation
starfish were removed from an enclosed (c) Reward in the form of Nectar
intertidal area, the result was: (d) Place for laying eggs
(a) Increase in diversity of invertebrates 67. The plant Cuscuta is a:
(b) Extinction of many invertebrate (a) Partial root parasite
species (b) Partial stem parasite
(c) Inability of the Pisaster to enter the (c) Total root parasite
area again (d) Total stem parasite
(d) Replacement of Pisaster by other 68. No predator can become proficient at
starfish acquiring prey because:
64. A species whose distribution is (a) Predators are not as intelligent as
restricted to a small geographical area prey
because of the presence of a (b) Predators are too large to be fast
competitively superior species is found enough
to expand its distributional range (c) Prey populations evolve more
dramatically when the competing rapidly than predator populations
species is experimentally removed. This (d) Prey populations evolve
is called: antipredatory traits.
(a) Competitive Exclusion 69. In general, which of the following is not
(b) Competitive Release an adaptation seen in parasites in
(c) Competitive Supremacy accordance with their life style?
ECOLOGY 79

(a) Loss of unnecessary sense organs (b) They keep prey populations under
(b) Presence of adhesive organs control
(c) Low reproductive capacity (c) They help in the stabilization of the
(d) Loss of digestive system ecosystems
70. Which of the following is not a function (d) They decrease the species diversity
of predators? in a community
(a) They act as conduits for energy
transfer across trophic levels
80 ECOSYSTEM

Answers Key
EXERCISE (Basic Exercise)
1. (a) 2. (a) 3. (b) 4. (a) 5. (d)
6. (a) 7. (a) 8. (b) 9. (b) 10. (d)
11. (d) 12. (c) 13. (a) 14. (b) 15. (c)
16. (a) 17. (d) 18. (b) 19. (a) 20. (b)
21. (d) 22. (b) 23. (a) 24. (a) 25. (b)
26. (b) 27. (c) 28. (a) 29. (a) 30. (a)
31. (d) 32. (c) 33. (b) 34. (d) 35. (b)
36. (b) 37. (a) 38. (c) 39. (b) 40. (a)
41. (a) 42. (b) 43. (a) 44. (b) 45. (a)
46. (a) 47. (a) 48. (d) 49. (b) 50. (c)
51. (d) 52. (d) 53. (c) 54. (b) 55. (d)
56. (d) 57. (d) 58. (c) 59. (a) 60. (c)
61. (c) 62. (b) 63. (b) 64. (b) 65. (d)
66. (a) 67. (d) 68. (d) 69. (c) 70. (d)