Food web

Ayesha Ghaffar B11-26

Nimrah Zahid B11-17

Jannat Iftikhar B11-16

Amber Rubab B11-14

Tayyaba Latif B11-20

Aqsa Malik B 11-23

A group of organisms living in the

same environment.

Producers

Consumers

i. Primary consumers

ii. Secondary consumers

iii. Tertiary consumers

iv. Quaternary consumers

Decomposers

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.

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.

Animals that eat ONLY PLANTS are called

herbivores and are also called primary

consumers.

Animals that eat OTHER ANIMALS are called

carnivores. Carnivores that eat herbivores are

called secondary consumers.

Carnivores that eat other carnivores are called

tertiary consumers.

organisms that eat tertiary consumers.

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.

History :Food chains were first

introduced by the African-Arabscientist and philosopher Al-Jahizin the 9th century and laterpopularized in a book publishedin 1927 by Charles Elton, whichalso introduced the food webconcept.

A food chain represents the series oftransfer of energy in different levels ofcommunity.

Example:

Grass Grasshopper Snake

Hawk Fungi

The trophic level of an organism is the

position it occupies in a food chain.

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.

A node is one of the words/pictures that thearrows go toward or away from. A node mayrepresent an individual species, or a group ofrelated species or different stages of a singlespecies (such as one node for adult frogs and asecond for juvenile tadpoles).

A link connects two nodes. Arrows representlinks, and always go from prey to predator (as infood chain).

The lowest trophic level are called basal species

The highest trophic level are called toppredators.

Movement of nutrients is cyclic but of energy isunidirectional and non-cyclic.

Topological webs

Flow webs

Interaction webs

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!

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.

An interaction web is similar to a topologicalweb, but instead of showing the movementof energy or materials, the arrows show howone group influences another.

In interaction food web models, every linkhas two direct effects.

One of the resource on the consumer andone of the consumer on the resource.

The effect of the resource on the consumeris positive, (the consumer gets to eat) andthe effect on the resource by the consumeris negative (it is eaten).

Soil food web

Aquatic food web

Food web in forest

Food web of grassland

Food web in terrestrial and aquatic

ecosystem

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.

The soil food web is similar to the food chain,except that the typical food chain is linear, whilethe soil food web shows everything that can eator be eaten in a cyclical relationship.

Soil is composed of two parts:

Minerals, which make up the nonliving portionof the soil.

Minute creatures, also called soil biota, whichbring the soil to life. Soil biota come in manyforms. Some help to build healthy soil andsupport healthy plants, and these are consideredbeneficial. Others can cause many problems andare considered pathogens.

BACTERIA:

Our native soils are full of bacteria, both beneficialand pathogenic. In general, they help water movethrough the soil more easily, they recycle organicmatter, and they help ward off soil diseases. Thereare many types of bacteria, but one of the mostimportant groups is the nitrogen-fixing bacteria. Theycreate a waste product called bacteria manure thatadds new forms of organic content to soil. Manyplants absorb nutrients most efficiently through thisbacterial waste product, so the more nitrogen-fixingbacteria in the soil, the better it is. Bacteria andbacteria’s waste products are also eaten by fellowsoil dwellers of many kinds, so they feed otherorganisms in the soil in addition to feeding plants.

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.

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

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.

The main function of Aquatic food chain is

that:

It depicts the structure of the living

components of hydrosphere.

It transfers energy and materials.

Ecosystem maintain themselves by cycling

energy and nutrients obtained from external

sources.

In ecology, energy flow, also called

the calorific flow, refers to the flow

of energy through a food chain.

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.

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 .

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).

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%.

Terrestrial not more than 5.

Marine not more than 7.

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.

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.

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

Therefore, primary consumers get about 10%

of the energy produced by autotrophs, while

secondary consumers get 1% and tertiary

consumers get 0.1%.

An ecological pyramid (or tropic pyramid) is

a graphical representation designed to show

the biomass or biomass productivity at each

tropic level.

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.

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.