The document discusses food chains and food webs. It defines producers, consumers, and decomposers. It explains how energy and nutrients flow through ecosystems via trophic levels from primary producers to higher level consumers. Food webs are more complex than linear food chains and illustrate interconnecting feeding relationships in a community. Destabilizing food webs through human activities can negatively impact ecosystem functioning.

1. University of the Punjab
Lahore

4. A group of organisms living in the
same environment.

5.  Producers
 Consumers
i. Primary consumers
ii. Secondary consumers
iii. Tertiary consumers
iv. Quaternary consumers
 Decomposers

6.  Plants are called producers because they are
able to use light energy from the Sun to
produce food (sugar) from carbon dioxide
and water. The process by which plants make
food is called photosynthesis.

7.  Animals cannot make their own food so they
must eat plants and/or other animals. They
are called consumers.
 There are mainly three groups of consumers
but sometimes we also include quaternary
consumers also.

8.  Animals that eat ONLY PLANTS are called
herbivores and are also called primary
consumers.

9.  Animals that eat OTHER ANIMALS are called
carnivores. Carnivores that eat herbivores are
called secondary consumers.

10. Carnivores that eat other carnivores are called
tertiary consumers.

11.  organisms that eat tertiary consumers.

12.  A final link in the food chain are
decomposers which break down the organic
matter of the tertiary consumers (or
whichever consumer is at the top of the
chain) and release nutrients into the soil.

15. History :
Food chains were first
introduced by the African-Arab
scientist and philosopher Al-Jahiz
in the 9th century and later
popularized in a book published
in 1927 by Charles Elton, which
also introduced the food web
concept.

16.  A food chain represents the series of
transfer of energy in different levels of
community.
 Example:
Grass Grasshopper Snake
Hawk Fungi

18.  The trophic level of an organism is the
position it occupies in a food chain.

21.  Food web can be defined as, "a network of food
chains which are interconnected at various
tropic levels, so as to form a number of feeding
connections amongst different organisms of a
biotic community".
 It is also known as consumer-resource system.
 It is a graphical description of feeding
relationships among species in an ecological
community. It is also a mean of showing
how energy and materials (e.g., carbon) flow
through a community of species as a result of
these feeding relationships.

23.  A node is one of the words/pictures that the
arrows go toward or away from. A node may
represent an individual species, or a group of
related species or different stages of a single
species (such as one node for adult frogs and a
second for juvenile tadpoles).
 A link connects two nodes. Arrows represent
links, and always go from prey to predator (as in
food chain).
 The lowest trophic level are called basal species
 The highest trophic level are called top
predators.
 Movement of nutrients is cyclic but of energy is
unidirectional and non-cyclic.

25.  Topological webs
 Flow webs
 Interaction webs

26.  Early food webs were topological. They
simply indicate a feeding relationship.
 One problem…
 Suppose individuals of species X eat 10,000
individuals of species Y, and one X is seen
eating one individual of species Q. A
topological web then shows an arrow from Y
to X, and an arrow from Q to X. This makes it
look as though both prey are equally
important to X. But they’re not!

27.  Bioenergetic webs, or flow webs, include
information on the strength of the feeding
interaction. This can be done in one of two
ways:
 Vary the size of the arrow. Thicker arrows
represent a larger percentage of the diet.
(interactions where more prey are eaten or
where more energy flows upward).
 The amount of energy moving between
nodes next to the arrow.

28.  An interaction web is similar to a topological
web, but instead of showing the movement
of energy or materials, the arrows show how
one group influences another.
 In interaction food web models, every link
has two direct effects.
 One of the resource on the consumer and
one of the consumer on the resource.
 The effect of the resource on the consumer
is positive, (the consumer gets to eat) and
the effect on the resource by the consumer
is negative (it is eaten).

29.  Soil food web
 Aquatic food web
 Food web in forest
 Food web of grassland
 Food web in terrestrial and aquatic
ecosystem

30.  The soil food web is the community of
organisms living all or part of their lives in
the soil.
 It describes a complex living system in the
soil and how it interacts with the
environment, plants, and animals.

31.  The soil food web is similar to the food chain,
except that the typical food chain is linear, while
the soil food web shows everything that can eat
or be eaten in a cyclical relationship.
 Soil is composed of two parts:
 Minerals, which make up the nonliving portion
of the soil.
 Minute creatures, also called soil biota, which
bring the soil to life. Soil biota come in many
forms. Some help to build healthy soil and
support healthy plants, and these are considered
beneficial. Others can cause many problems and
are considered pathogens.

32.  BACTERIA:
 Our native soils are full of bacteria, both beneficial
and pathogenic. In general, they help water move
through the soil more easily, they recycle organic
matter, and they help ward off soil diseases. There
are many types of bacteria, but one of the most
important groups is the nitrogen-fixing bacteria. They
create a waste product called bacteria manure that
adds new forms of organic content to soil. Many
plants absorb nutrients most efficiently through this
bacterial waste product, so the more nitrogen-fixing
bacteria in the soil, the better it is. Bacteria and
bacteria’s waste products are also eaten by fellow
soil dwellers of many kinds, so they feed other
organisms in the soil in addition to feeding plants.

33.  EARTHWORMS:
 Worms are among the most beneficial of soil
dwellers. Sadly, they are easily harmed or
killed by exposure to many common
pesticides and herbicides.
 Actually they are the soil builders. They do
the mixing of soil. They tunnel through heavy
soil to let air get down to plant roots.

35.  food chain which occurs in aquatic water is
called aquatic food chain.
 e.g.
Algae → Protozoa → Small
Insects → Large aquatic
Insects → Small fish → Large fish

36.  A balanced food web is essential to any
marine or fresh water system, and can be an
indicator of habitat quality.
 Planktonic algae are the foundation of
aquatic food webs.
 . The size and diversity of the planktonic
algae community determines the diversity of
the zooplankton community that can be
supported as well as the small fish
community.

38.  The main function of Aquatic food chain is
that:
 It depicts the structure of the living
components of hydrosphere.
 It transfers energy and materials.

44.  Ecosystem maintain themselves by cycling
energy and nutrients obtained from external
sources.

45. In ecology, energy flow, also called
the calorific flow, refers to the flow
of energy through a food chain.

47.  Gross primary production consists of the
amount of light energy that is converted to
chemical energy by photosynthesis per unit
of time. This chemical energy is going to two
places-- respiration and growth of new
biomass.

48.  Some fraction of this fixed energy is used by
primary producers for cellular
respiration and maintenance of existing
tissues. The remaining fixed energy is
referred to as net primary production .

49.  H. T. Odum analyzed the flow of energy
through a river ecosystem in Silver Springs,
Florida.
 His findings are shown here. The figures are
given in kilocalories per square meter per
year (kcal/m2/yr).

51.  At each trophic level, Net production is only
a fraction of gross production because the
organisms must expend energy to stay alive.
 Much of the energy stored in net production
was lost to the system by
 decay
 being carried downstream
 Conversions efficiencies are always much less
than 100%.

52.  Terrestrial not more than 5.
 Marine not more than 7.

53.  Solar energy is fixed by the photoautotrophs,
called primary producers, like green plants.
 Primary consumers absorb most of the
stored energy in the plant through digestion,
and transform it into the form of energy they
need, such as adenosine triphosphate (ATP),
through respiration.

55.  Secondary consumers, carnivores, then
consume the primary consumers, although
omnivores also consume primary producers.
 Tertiary consumers, which may or may not be
apex predators, then consume the secondary
consumers, with some energy passed on and
some lost, as with the lower levels of the
food chain.

56.  A final link in the food chain are
decomposers which break down the organic
matter of the tertiary consumers (or
whichever consumer is at the top of the
chain) and release nutrients into the soil.
 The energy is passed on from trophic level to
trophic level and each time about 90% of
the energy is lost

57.  Therefore, primary consumers get about 10%
of the energy produced by autotrophs, while
secondary consumers get 1% and tertiary
consumers get 0.1%.

59.  An ecological pyramid (or tropic pyramid) is
a graphical representation designed to show
the biomass or biomass productivity at each
tropic level.

62.  Food webs distinguish levels of producers and
consumers by identifying and defining the
importance of animal relationships and food
sources, beginning with primary producers such
as plants, insects and herbivores.
 Food webs are important tools in understanding
that plants are the foundation of all ecosystems
and food chains, sustaining life by providing
nourishment and oxygen needed for survival and
reproduction.
 In short the food web provide stability to the
ecosystem.

63.  man is disturbing the food chain and making
it short.
 The shortening of food chain due to man’s
activities leads to imbalance in the
functioning of an ecosystem and ultimately
the biosphere.