Organisms and

population
 He
What is the Age pyramid? What are
the different types of age pyramids?
-
Ans: In a population of an organism, the geometrical diagrammatic
representation of different age groups is referred to as the Age of pyramids.
-

- -
These are of three types:-
-

i) Expanding pyramid:- It is a broad-based, triangular pyramid that

represents a population containing a large number of young people. It is a
rapidly expanding population with a high birth rate.

...
ii) Stable pyramid:- A moderate proportion of young to old is represented by
-
this pyramid. As the rate of growth becomes slow & stable i.e.- pre-
- -
reproductive & reproductive age groups become more or less equal in size.
- -

iii) Declining Pyramid:- The type of pyramid of population decreasing in size is

--
characterized by a narrow base because there are fewer pre-reproductive
- -

individuals than in the other two age categories.

-
 I -

[ I
>
-

Stable
Expanding
Declining
 Birth rate

Death rate
Population attributes
Sex Ratio

Age distribution
I with Rate
It refers to per capita births
individuals added
We of
Natality Lo of individuals
[B]
-

existing
-
.

Rate -
per capitan deaths
individuals died
No .

of
Mortality DI
of individuals
=

Total no
 artio
·
atio
-
A
population has a seas

a) Attribution
Percent individuals of different
-

ages
The shape of the pyramids reflects the growth status of the
population -whether it is
a) Growing
b) Stable
c)Declining
Population size or population density (N):
Number of individuals of a species per unit area or volume
-

E.g. population density of Siberian cranes at Bharatpur

-
wetlands in any year is <10. In some cases, population size
-

is measured in % cover or biomass.

-

Total number is a difficult measure for a huge population.

In such cases, relative population density (without knowing
-

--
absolute population density) is used.
-
In some other cases, indirect estimation of population sizes is
-
performed. E.g. Tiger census in national parks & tiger reserves
--
based on pug marks & fecal pellets
-
In an area, if there are 200 Parthenium plants but only a single
-
huge banyan tree with a large canopy, stating that the population
-

density of banyan is low relative to that of Parthenium amounts to

-

underestimating the enormous role of the Banyan in that

-

community.
-

In such cases, the per cent cover or biomass is a more meaningful

-
measure of the population size. Total number is again not an easily
- -

adoptable measure if the population is huge and counting is

-

impossible or very time-consuming

-
 The four basic processes that fluctuate the population
density. -

y Natality
(B]

- Increase S
a) Mortality [D

of Immigration [I] X
- Decreases
4) Emigration [E
POPULATION GROWTH
Population size changes in time, depending-
on various factors like
-
food availability, predation pressure & weather
--

4 basic processes that fluctuate the population density

(1). Natality (B): It is the number of births in a population during

-
a given period
(
(2). Mortality (D): It is the number of deaths in a population during
-

a given period.
-
(3). Immigration (I): It is the number of individuals of the same species
-

that have come into the habitat from elsewhere during a given
-
time period.

(4). Emigration (E) : It is the number of individuals of the population

-
who left the habitat and gone elsewhere during a given time period.
--
 I
Immigration
(I)

B +
O D

+ -
O
Natality O Population
Density (N)
Morality
Mortality
⑰
(D)
(B)
6
-

Emigration
(E)

E
If N is the population density at time t,
then its density at time t+1 is,
-

Nt+1=Nt+ [(B+I)- (D+E)]

#Neteete
POPULATION GROWTH
MODELS
 GROWTH MODELS
Exponential versus logistic population growth
Population Density

exponential growth logistic growth

carrying capacity (K) of environment
wil -

eit
population size

population size
a
resome
un
0 Time 0 Time

S-shaped s-shaped
 Exponential growth

Resource (food and space) availability is

-

obviously essential for the unimpeded growth of a

-
population. Ideally, when resources in the habitat are
-

unlimited, each species has the ability to realise fully its

-
innate potential to grow in number, as Darwin observed
- -

while developing his theory of natural selection. Then the

-

population grows in an exponential or geometric fashion

--
suponentialLet
Time
I Growth Model
Exponential -

shaped
I
-

I ame

↓N =vN
-

dt

Where , v in the is
"Intrinsic
eqn -

natural increase
rate
- I
Any species growing exponentially under unlimited resource
-

conditions can reach enormous population densities in a short

time.
-
-
-

Darwin showed how even a slow growing animal like elephant

-

could reach enormous numbers in the absence of checks. The

- -
following is an anecdote popularly narrated to demonstrate
-

dramatically how fast a huge population could build up when

-
growing exponentially
-

-
Logistic Growth

There is no population in nature having unlimited resources for

exponential growth. This leads-
to competition between individuals
for limited resources.
-

In nature, a given habitat has enough resources to support a

-
maximum possible number, beyond which no further growth is
-
possible. It is called Carrying capacity (K)

capacity
--

Carrying (k)
No population of any species in nature has at its
disposal unlimited resources to permit exponential growth.

This leads to competition between individuals for limited resources.

Eventually, the ‘fittest’ individual will survive and reproduce.

The governments of many countries have also realised this fact and
introduced various restraints with a view to limit human population
growth. In nature, a given habitat has enough resources to support a
maximum possible number, beyond which no further growth is possible.
Let us call this limit as nature’s carrying capacity (K) for that species in
that habitat
No population of any species in nature has at its
disposal unlimited resources to permit exponential growth.

This leads to competition between individuals for limited resources.

Eventually, the ‘fittest’ individual will survive and reproduce.

The governments of many countries have also realised this fact and
introduced various restraints with a view to limit human population growth.

In nature, a given habitat has enough resources to support a maximum

possible number, beyond which no further growth is possible. Let us call this
limit as nature’s carrying capacity (K) for that species in that habitat
 Model
2) Logistic
--
Growt
k
.
(origin
apau
Sigmad ↓
=
- curve

- vNk
Lk3
-
N
=

At
-

capacity
migl
-

Verhulst-Peaal Mode
A population with limited resources ———a lag phase,
followed by phases of acceleration & deceleration and finally an
asymptote, when the population density reaches the carrying capacity.

This type of population growth is called Verhulst-Pearl Logistic Growth. It

is described by following equation: -> sigmoid curve : S'ae

( )
dN/dt = rN K-N
K
Where N = Population density at time t
r = Intrinsic rate of natural Increase
K = Carrying capacity

Since resources for growth for most animal populations are finite the
logistic growth model is more realistic one.
Some organisms breed only once in their lifetime (Pacific salmon fish,
bamboo) while others breed many times during their lifetime (most birds
and mammals).

Some produce a large number of small-sized offspring (Oysters, pelagic

fishes) while others produce a small number of large-sized offspring
(birds, mammals).

So, which is desirable for maximising fitness? Ecologists suggest that life
history traits of organisms have evolved in relation to the constraints
imposed by the abiotic and biotic components of the habitat in which
they live. Evolution of life history traits in different species is currently
an important area of research being conducted by ecologists
POPULATION INTERACTIONS
3
Pe

Species A Species B Name of Interaction

+ + Mutualism

- - Competition
+ - Predation

+ - Parasitism

+ 0 Commensalism
- 0 Amensalism
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.

And then, how will the plant manage pollination without an animal
agent? It is obvious that in nature, animals, plants and microbes do not
and cannot live in isolation but interact in various ways to form a
biological community. Even in minimal communities, many interactive
linkages exist, although all may not be readily apparent
Intraspecific Interaction - In blooz spas.

Interspecific Interaction Two diff spac

 --

I competition
-

Both the harmed

species
are
-

of Parasitism + -

benefitted
One species (parasite) is

harmed
-

and other species (host) is

-
.
 -
Spredator
+

Predation secies
One
/other
3) :

is bebefitted arch species

-
harmed
(pray)
-
is o

O
harmed
-

4Iand Amenza lism : One species

is
-

live
the other is
-
interacting species
-
closely together .
Predation
Predator Catches Preg
W for food which will control over population of a
species. It helps energy flow in a food chain.
Predators are important for ecosystem. When starfish Pisaster was
removed from its ecosystem, 10 Species of invertebrates extinct from
that habitat.
Predation is nature’sway of transferring to higher trophic levels
the energy fixed by plants.

Predators keep prey population under control

Predators maintain species diversity in a community.

For plants,herbivores are the predators. About 25
percent of all insects are known to be phytophagous
ie; feeding on plant sap and other parts of plants.
Competition

The abington tortoise in Galapagos Islands became

extinct within a decade after goats were introduced on
the island, due to greater browsing efficiency of the
goats.
Competition
When resource is limited, there may be inter specific of intraspecific
competition.
Gause in his experiment found that when resources are limited superior
species will eliminate other species.
eg: When Goats introduced into Galapagos Island, Abingdon tortoises
cohere extinct
Competitive release :
- A species whose distribution is restricted to a small geographical
area due to superior Species, is found to expand its distributional
range dramatically when competing species is removed.

Connell's elegent field experiment:

- showed that supertor barnacle called Balanus dominates intertidal
area of Scotland and excludes smalled barnacles Chathamalus.

Gause's Competitive Exclusion Principle 1.-

Two closely related species competing for the same V
sesocuces cannot co-exist
indefinitely and competitively. inferior one will be eliminated eventually.
Resource partitioning
If two species compete for the same resource, they could
avoid competition by choosing, for instance,
differenttimesfor feedingordifferentforagingpatterns.
↑

Warblers
Eg :
Parasitism
free lodging & meals from host species.
Mostly host & parasite co-evolve.
Parasites have parasitic adaptations like hooks, Suckers, absence of
sense organs, loss of digestive system, high reproduction capacity etc.

Ectoparasite lice on humans, ticks on dogs, Cuscuta.

Endopalasite - live f
bluke
Brood parasitism - Cuckoo ley egg in nest of Crow.
 Adaptations of parasites
mob
A Loss of sense organs
Pres ence of adhesive organs or suckers to cling on
-

A -

*
to the host.
* Loss of digestive system
-

High reproductive capacity

* -
 Parasites that feed on the external surface of the host organism are called
Ectoparasites.
-

The most familiar examples of this group are the lice on humans and ticks on dogs.
Many marine fish are infested with ectoparasitic copepods. Cuscuta, a parasitic plant
that is commonly found growing on hedge plants, has lost its chlorophyll and leaves in
the course of evolution. It derives its nutrition from the host plant which it parasitises.
-
-
-

The female mosquito is not considered a parasite, although it needs our blood for
reproduction.
- -

Endopa
-
rasites are those that live inside the host body at different sites (liver, kidney,
lungs, red blood cells, etc.).

- Brood parasitism in birds is a fascinating example of parasitism in which the

parasitic bird lays its eggs in the nest of its host and lets the host incubate them.
cuckoo (koel) and the crow
Commensalism
One species is benefited & other is neither hamed or benefited.
eg: Orchid Cepiphyte) on mango., Cattle egret & grazing Cattle,
--
sea anemone and clown fish.
-

Mutualism
Both species one benefited.
-
eg: Lichen, Mycorrhizae, pollinating insect & plant
-
Commen Sa lism Clown Sea
4
fish
:

- anemone

Examples :
[t (0)
tree
1 .
Orchic-
(H)
MangoI
Barnacks -
Whale
2
(0)
.

C3
Cattle
3 - Cattle
(t)
Egret -

(0)
 Fig tree& Wasp
I

al Lichens
- -> Algas Fungi
+

Mycorhiza > Roots + Fungs

C
4) ‘Sexual deceit’of Ophyrus orchid
-

Pollination
->
Pseudocopulation
Helps in
-

Bee
-> Male
(a) Which type of growth curve does it represent?
(b) What do the following notations represent?
(a) N (b) r (c) K

.Given below is a table which shows inter- specific interaction of populations.

We assigned '+' for beneficial, for detrimental and 'O' for neutral interaction.
Fill in th blanks
Species A Species B Name of Interaction
+ Parasitism
-
- - competition
+ + Mutualism
Commensalism
+ 0
- 0
Ammensalism
Name the type of interaction that is
detrimental to both the species.
What type of interaction is shown by
sparrows eating the seeds?
What is Brood parasitism? Give an
example. What adaptation evolved in
this phenomenon?
Brood parasitism refers to the phenomenon in which one bird species by
its eggs in the nests of another bird species Evolution has occurred in
such a way the eggs of the parasitic birds resemble those of the host
bird in size, color, etc to avoid host bird detecting the foreign eggs &
ejecting them from the nest e.g. cuckoo bird lays eggs in the nest of
crow.

It is considered as a parasitic type of interspecific interaction because

in this relationship the parasite i.e. eggs of cuckoo birds depend on the
crow's nest for its food & shelter but the crow is harmed because
there is competition for limited food and shelter amongst the crow's
egg & cuckoo's egg thus, in parasitic interspecific interaction the
parasite is benefited while the host is harmed.
Which one of them is ideal for a
population & why?
Ans: Among the three, a stable
population is ideal because it has an
identical birth death rate.
Orchid flower, Ophrys co-evolves to maintain a
resemblance of its petal to female bees. Explain
how and why does it do so?
Ans: They employ 'Sexual deceit'. one petal bears an uncanny
resemblance to the female of the bee. The male bee is
attracted to what it perceives as a female 'pseudocopulation,'
during which pollen dusted on the male bee is a body. A male
bee transfers pollen to another flower when the same bee
pseudocopulation with another flower. Ophrys does this in
order not to make pollination success reduce unless it co-
evolves with the female bee.
Describe the logistic growth model of the
population along with a suitable curve.
Why is this curve more realistic?
The logistic growth curve shows a sigmoid or an S-shaped curve. It has
three phases:-

i) Lag-phase:- It is considered to be an early phase showing little or no

growth. The lag phase is one in which the under the population of cells
adapt to or stabilize with the growth conditions before embarking on their
multiplication.

ii) Log phase or Exponential phase:- It is the middle phase of rapid or

geometric rise. Once stabilized cells start to multiply rapidly when the small
population is stabilized, the multiply becomes faster because of the plenty
of food & other requirements of life.
iii) Stationary phase or steady phase:- Soon after the
number of food decreases in proportion to the number
of cells & this results in the onset of the stationary
phase.

So in this phase, the number of new cells formed becomes

approximately equal to the number of cells dead & thus there is no
net increase in the number of cells
-

c dN
million
2005
14)
-

>
-

dt
loyrs
=

z B >
-
0 .
028
-

0 00$
-
D
.

0028-0
z = 0 . 020
- 2

2015-

00
 N205- Noos
= N dN =

14 Y

dN
a
To=
0 020
. .

x14
=

dN 0 020 X10 X
14
.

dN =
Nois - N20s
=> N205 =
dN + Not
2·
8 + 14 = 16 .
8 =
If milor
z
&
-

-
G
 dN UN mi
020x14
=

E = 0 .

Eloy

-
-
-

e
2 8
Naois-Nivoj
= .

dN + Vort

>
- Nos
=

-
= -

-
-

-
-

mensalism
 - - -

-
-

-
- -

- -

- -

-
-

-
4)

t
-

-
-

--

--
- -

-
-

-
--
-
--
-

-
&
--

--

--- ⑩
 -

--

-
 -

- - -
-
-

⑨
ECOSYSTEM
E
The term ecosystem was first coined by A G Tansley

The functional unit of nature, where living organisms

=
interact among them selves and also with the surrounding
physical environment.
-

Many ecologists regard the entire biosphere as a global

-

ecosystem
-
 ECOSYSTEM
Natural Artificial

Terrestrial Aquatic Man made ecosystem

Forest Pond Crop fields

Grassland Lake Aquarium
Desert Wetland
River
Estuary
 ECOSYSTEM -Structure and Function
• Entire biosphere is regarded as global ecosystem.
In an ecosystem, biotic and abiotic components interact
-living
Non-living
and function as a unit.
• Vertical distribution of different species occupying different
levels is called stratification. E.g. In a forest, trees occupy top
strata (layer), shrubs the second and herbs & grasses the
bottom layers.

Emergent layer

Canopy layer

Understory layer

Shrub layer

Ground layer
 Structure of Ecosystem

Habitat
-> specific area occupied by the
living
organisms
Species composition ->Identification & enumeration
of plant and animal species

4
Stratification -

Based nutrition of food

on -
Trophic levels
,
->

organisms occupy
a
specific placein
- the food chain

st Standing crop and standing state

-
Vertical distribution of different species occupying
-

different levels is called Stratification.

-

For example, trees occupy top vertical strata or layer of

-

a forest, shrubs the second and herbs and grasses occupy

-
-
the bottom layers.
-
 1
Emergent Layer

Canopy Layer

Understory Layer

Immature Layer

Herb Layer
 Standing crop and standing state

Each
- -
tropic level has a certain mass of living material at a
particular time called as the standing crop.
-

Biomass or no. of organisms in a unit area.

Biomass is expressed in terms of dry weight.

Nutrients in soil- standing state

 Structure and function of ecosystem.
• The structure of ecosystem consists of biotic and abiotic
components.
The abiotic components are non-living components.
They are air, water, solar radiation, temperature etc.
 Levels
tropic
-
The biotic components are

Producers : synthesis there own food. Photoautotroph

and chemoautotroph.
Consumers : pri consumer (herbivores), sec - consumer
(pri.Carnivores), tertiary consumer (sec.Carnivores) etc.
Decomposers : Bacteria and fungi.
The components of the ecosystem are seen to function as a unit
when you consider the following aspects:

(i) Productivity
(ii) Decomposition
(iii) Energy flow
(iv) Nutrientcycling.
PRODUCTIVITY

Productivity
The rate of biomass production per unit area during
a given period of time is called productivity.

It is measured in terms of weight (g−2) or energy (kcal m−2).

It is used to compare productivity of different ecosystems.

Primary productivity:
It is the amount of biomass produced per unit area in
a given time period by Plants during Photosynthesis.
GPP-Gross Primary Productivity : It is the rate of production
of organic matter during photosynthesis.
NPP-Net Primary Productivity.
R-respiration loss.
<PP -
R =
NPP
z
-

GPP-R = NPP
-

GPP is not equal to NPP bcoz, considerable amount of GPP

-- -
is utilized by plants in respiration
-
 -

--

Brass
-

>
hopper
1
-
Frog >
- Snake
-

- -

-
Discuss the main reason for the low
-

productivity of ocean.
-
Reason for ocean'slow productivity:
In aquatic ecosystems,
-

the limiting factor for productivity is light as the producers

--

depend on light which is scanty in deeper layers.

-

The amount of minerals in oceanic water is also low compared

- -
to soil in the terrestrial ecosystem.
-

The producers in the ocean ecosystem are mainly free floating

-
phytoplankton, which are either very small or unicellular, compared
-
to terrestrial system in which the producers are big multicellular plants
-
having many chlorophyll containing cells.
-
Photosynthetic capacity is a measure of the maximum rate
-

at which leaves are able to fix carbon during photosynthesis.

- -

It is typically measured as the amount of carbon dioxide that

-
is fixed per metre squared per second.
-

The photosynthetic capacity of the terrestrial plants is more

-

compared to very low photosynthetic capacity of the producers

--
of the oceanic ecosystem.
-
Therefore, despite occupying the 70%
of the surface of the earth, the productivity
of ocean is very low.
The productivity of land is 170 billion tons while
the productivity of the ocean is only 55 billion tons.

Coral reefs, sea grasses and brown alqal beds are

the systems in marine waters offering maximum
productivity.

In cool waters, dense forests are formed by the kelps

(brown algae belonging to genera Macrocystis and Laminaria)
in the sublittoral zone of the rocky coasts.
1) In the second step of trophic level, the energy storage
is primarily associated with

(a) gross primary productivity

(b) net primary productivity
(c) secondary productivity
(d) none of the above
2) The second trophic level in a lake is...............

(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes
3)Food chain in which microorganisms breakdown the food
formed by primary producers

(a) Parasitic food chain

(b) Detritus food chain
(c) Consumerfoodcahin
(d) Predator food cahin
4)What is true of ecosystem?

(a) Primary consumers are least dependent upon producers

(b) Primary consumers out number producers
(c) Producers are more than primary consumers
(d) Secondary consumers are the largest and most powerfull
5) Which of these statements is correct?

(a) The base of the energy pyramid contains the largest

trophic level.
(b) About 10% of energy available in food is actually incorporated
into any trophic level.
(c) Humans are at the top of energy pyramids.
(d) All of these
 DECOMPOSITION
If
Earthworm being referred to as the farmer’s ‘friend’
the earthworm being referred to as the farmer’s ‘friend’
-

This is so because they help in the breakdown of complex

organic matter as well as in loosening of the soil.
-

--

Similarly, decomposers break down complex organic matter into -

-
inorganic substances like carbon dioxide, water and nutrients
and the process is called decomposition.
-
-

-
Decomposition
flowers
Detritus (eedead remains7 ,

① Fragmentation
Defrivores
(Earthworms) ② leaching
③ Catabolism
⑤
# humification ,
mineralization
I

particles
-
smaller
Dead plant remains such as leaves, bark, flowers and
-

dead remains of animals, including fecal matter,

-

constitute detritus, which is the raw material for

-

decomposition.
-

The important steps in the process of decomposition are

fragmentation, leaching, catabolism, humification and
mineralisation.
 Detritivores

&
(e.g., earthworm) break down detritus into smaller particles.
This process is called fragmentation.
-

* By the process of leaching, water- soluble inorganic nutrients go

down
- into the soil horizon and get precipitated as unavailable salts.

* Bacterial and fungal enzymes degrade detritus into simpler

---
inorganic substances. This process is called as catabolism.
-
A Humification and mineralisation occur during decomposition in the soil.
--

*
Humification leads to accumulation of a dark coloured amorphous
substance called humus that 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.

--

# The humus is further degraded by some microbes and release of

inorganic nutrients occur by the process known as mineralisation.
- -

- -
* Decomposition is largely an oxygen-requiring process. The rate of -

decomposition is controlled by chemical composition of detritus

and climatic factors.
-
-

** In a particular climatic condition, decomposition rate is slower if

detritus is rich in lignin and chitin, and quicker, if detritus is rich
-

in nitrogen and water-soluble substances like sugars.

-

--

* Temperature and soil moisture are the most important climatic

-
factors that regulate decomposition
-

through their effects on the activities of soil microbes. Warm and moist environment favour decomposition whereas

low temperature and anaerobiosis inhibit decomposition resulting in build up of organic materials.
-
Decomposition is largely an oxygen-requiring process. The rate of decomposition
is controlled by chemical composition of detritus and climatic factors.

In a particular climatic condition, decomposition rate is slower if detritus is

rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-
soluble substances like sugars.
Temperature and soil moisture are the most important climatic factors that
regulate decomposition through their effects on the activities of soil microbes.
-

Warm and moist environment favour decomposition whereas low temperature

and anaerobiosis inhibit decomposition resulting in build up of organic
--

materials. -
-
State why at the herbivore level, the rate of
-
assimilation of energy is called as secondary
-

productivity.
It is because the biomass available to the
-

consumers
-
for further consumption is formed by
the autotrophs as a product of primary
-

productivity.
-
D i f f e r e n t i a t e b e t w e e n h u m i fi c a t i o n a n d
-

mineralization.
-
-

- -

-
-

-
Write a difference between net and gross
primary productivity
Define decomposition. Describe the many steps
involved in decomposition.
ENERGY FLOW
I

Except for the deep sea hydro-thermal ecosystem, sun is the only
-

source of energy for all ecosystems on Earth.

-

e
Of the incident solar radiation less than 50 per cent of it is
-
photosynthetically active radiation (PAR).
-

We know that plants and photosynthetic bacteria (autotrophs), fix

-
Sun’s radiant energy to make food from simple inorganic materials.
 -
Plants capture only 2-10 per cent of the PAR and this small
amount of energy sustains the entire living world.
-

So, it is very important to know how the 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.

-
So you find unidirectional flow of energy from the sun to
producers and then to consumers.

Further, ecosystems are not exempt from the Second Law of

thermodynamics.
They need a constant supply of energy to synthesise the
molecules they require, to counteract the universal tendency
toward increasing disorderliness.
The green plant in the ecosystem are called 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.
--
The chain or web is formed because of this
interdependency.
-

No energy that is trapped into an organism remains in it for

ever.

The energy trapped by the producer, hence, is either

passed on to a consumer or the organism dies. Death of
organism is the beginning of the detritus food chain/web.
All animals depend on plants (directly or indirectly) for their food
needs.
They are hence called consumers and also heterotrophs.
If they feed on the producers, the plants, they are called primary
consumers, and if the animals eat other animals which in turn eat
the plants (or their produce) they are called secondary consumers.

Likewise, you could have tertiary consumers too.

Obviously the primary consumers will be herbivores. ommon herbivores are insects, birds and mammals in

terrestrial ecosystem and molluscs in aquatic ecosystem.

The consumers that feed on these herbivores are carnivores, or
more correctly primary carnivores (though secondary consumers).

Those animals that depend on the primary carnivores for food

are labelled secondary carnivores.

A simple grazing food chain (GFC) is depicted below:

The detritus food chain (DFC) begins with dead organic matter. It
is made up of decomposers which are heterotrophic organisms,
mainly fungi and bacteria.

They meet their energy and nutrient requirements by degrading

dead organic matter or detritus.

These are also known as saprotrophs (sapro: to decompose).

Decomposers secrete digestive enzymes that breakdown dead and

waste materials into simple, inorganic materials, which are
subsequently absorbed by them.
In an aquatic ecosystem, GFC is the major conduit for energy
flow.

As against this, in a terrestrial ecosystem, a much larger fraction

of energy flows through the detritus food chain than through
the GFC.

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 interconnection of food chains make it a food web.

Trophic level

Organisms occupy a place in the natural surroundings or in a

community according to their feeding relationship with other
organisms.

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.
 6 -

C -

-o -

-
-

- 8 --
The important point to note is that the amount of energy
-

decreases at successive trophic levels.

-

When any organism dies it is converted to detritus or dead

biomass that serves as an energy source for decomposers.
-

- -

Organisms at each trophic level depend on those at the lower

-

trophic level for their energy demands.

-

-
 Standing crop and standing state
-

Each tropic level has a certain mass of living material at a

particular time called as the standing crop.

Biomass or no. of organisms in a unit area.

Biomass is expressed in terms of dry weight.

Nutrients in soil- standing state

Energy flow through different trophic levels
The ten percent rule of transfer of energy
Raymond Lindeman

- The ten -percent rule of transfer-of energy from one trophic

level to the next is being credited to Raymond Lindeman
(1942).
-

&

The 10 percent law of energy flow states that when the o

-
energy is passed on from one trophic level to another, only
-

10 percent of the energy is passed on to the next trophic

-

--
level.
The number of trophic levels in the grazing food chain is
-

restricted as the transfer of energy follows 10 per cent law

- -

– only 10 per cent of the energy is transferred to each

trophic level from the lower trophic level.
-

In nature, it is possible to have so many levels – producer,

-
herbivore, primary carnivore, secondary carnivore in the
grazing food chain
-

100005 100 05 1005 105

Green >
- Rabbit >
-
For -how ↑

lar
 ECOLOGICAL PYRAMIDS
ECOLOGICAL PYRAMIDS

The base of a pyramid

-
is broad and it narrows towards the apex. One
gets
--
a similar shape, whether you express the food or energy
relationship between organisms at different trophic levels.
-

This, relationship is expressed in terms of number, biomass or

-
energy. The base of each pyramid represents the producers or the first
- -
-

trophic level while the apex represents tertiary or top level consumer
--
The three types of ecological pyramids that are usually
studied are

(a) pyramid of number M

(b) pyramid of biomass andM
(c) pyramid of energy M
1
-
 .

upright pyramid
Pyramid of number

Grassland ecosystem
Pyramid of biomass
=
W

⑧
Pyramid of biomass shows a sharp decrease in biomass at higher
trophic levels
 .
Invertedpyramid

Inverted pyramid of biomass-small standing crop of phytoplankton supports large

- -
standing crop of zooplankton
-
 ht
Pyramid of energy allways aprig

C
O

An ideal pyramid of energy. Observe that primary producers convert only 1% of

the energy in the sunlight available to them into NPP
One must remember that the trophic level represents a functional
level, not a species as such.

A given species may occupy more than one trophic level in the same
ecosystem at the same time; for example, a sparrow is a primary
consumer when it eats seeds, fruits, peas, and a secondary
consumer when it eats insects and worms
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
Pyramid of energy is always upright, can never be inverted,
because when energy flows 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
Why is the length of a food chain in an ecosystem
=
generally limited to 3 - 4 trophic levels? Explain
with an example.
The amount of energy flow decreases with successive trophic levels as only
-

10% of energy is transferred from one trophic level to the next successive
trophic level. The energy is lost in the form of respiration and other vital
activities to maintain life. If more trophic levels are present the residual
-

energy will be limited and decreased to such an extent that it cannot further
-

support any trophic level by the flow of energy. so, the food chain is
-

generally limited to 3--4 trophic levels only.

-
Leaching is one of the important step of decomposition. During
-

leaching, which of the following nutrient go down into the soil

horizon?
- -

-
(a) Water soluble inorganic substance
(b) Water insoluble inorganic substances
(c) Water soluble organic substances
(d) Both water soluble organic substances and inorganic substances
Which of the following chemical will not reduce
the rate of decomposition of detritus
(a) Lignin
(b) Chitin
(c) Cutin
(d) Sugars
Ques. Energy transfer from one trophic level to
other, in a food chain, is

(a) 10% (b) 20% (c) 1% (d) 2%.

-
-
 -

--

-
---

--
-
①
⑪
 R =
GPP-NP GRE
NPP =
UPP = NPPAR
-

--

--

A- NVPP =
1254/m/day
B- NPP =
2157/m
--Sim
i

2
woodpecker
consumer

i Fleas

Animal 10
consumer
Insects

Grass
producer Free
 ⑳
-

- -
-
 Level
Trophic 2

Trophic Level 1

--
 -
③
-

-
 -

--
-

O
CASE

stupt ⑭