Ecological pyramids
An ecological pyramid is a graphical representation designed to show the number of
organisms, energy relationships, and biomass of an ecosystem. They are also called Eltonian
pyramids after Charles Elton, who developed the concept of ecological pyramids. Producer
organisms (usually green plants) form the base of the pyramid, with succeeding levels above
representing the different trophic levels Succeeding levels in the pyramid represent the
dependence of the organisms at a given level on the organisms at lower level.
Ecological pyramids represent the basic laws of energy. The first law of thermodynamics
states that the amount of energy remains constant. The second law states that "useful energy
decreases at each conversion." Therefore, ecological pyramids represent the transfer of energy
from one level to another. The laws of thermodynamics ensure the pyramid of energy to be a true
pyramid
There are three types of pyramids: of numbers, of biomass, and of energy.
Pyramid of Biomass
Biomass is organic (living) material. A pyramid of biomass is a representation of the amount of
energy contained in biomass, at different trophic levels for a particular time. It is measured in
grams per meter2, or calories per meter2. This demonstrates the amount of matter lost between
trophic levels. Each level is dependent on its lower level for energy; hence the lower level
determines how much energy will be available to the upper level. Also, energy is lost in transfer
so the amount of energy is less high up the pyramid.
There are two types of biomass pyramids: upright and inverted. An upright pyramid is one where
the combined weight of producers is larger than the combined weight of consumers. An example
is a forest ecosystem. An inverted pyramid is one where the combined weight of producers is
smaller than the combined weight of consumers. An example is an aquatic ecosystem.
Pyramid of Numbers
The pyramid of numbers represents the number of organisms in each trophic level. This pyramid
consists of a plot of relationships between the number herbivores (primary consumers), first level
carnivore (secondary consumers), second level carnivore (tertiary consumers) and so forth. This
shape varies from ecosystem to ecosystem because the number of organisms at each level is
variable
There are three types of Number Pyramids :Upright, partly upright and inverted. An aquatic
ecosystem is an example of upright pyramid where the number of organisms becomes fewer and
fewer higher up in the pyramid. A forest ecosystem is an example of a partially upright pyramid,
as fewer producers support more primary consumers, but there are less secondary and tertiary
consumers. An inverted pyramid of numbers is one where the number of producers are smaller
than the consumers . A parasitic food chain is an example.
Pyramid of Energy
The pyramid of energy represents the total amount of energy consumed by each trophic level. An
energy pyramid is always upright as the total amount of energy available for utilization in the
layers above is less than the energy available in the lower levels. This happens because during
energy transfer from lower to higher levels, some energy is always lost.
Food Chains.
The feeding of one organism upon another in a sequence of food transfers is known as a
food chain. Another definition is the chain of transfer of energy (which typically comes from the
sun) from one organism to another
Every organism needs to obtain energy in order to live. For example, plants get energy
from the sun, some animals eat plants, and some animals eat other animals.
Trophic levels
Trophic levels are the feeding position in a food chain such as primary producers,
herbivore, primary carnivore, etc. Green plants form the first trophic level, the producers.
Herbivores form the second trophic level, while carnivores form the third and even the fourth
trophic levels
A food chain is the sequence of organisms in an ecosystem where one organism eats
another to obtain nutrition. A food chain starts with the primary energy source, usually the sun or
boiling-hot deep sea vents. The next link in the chain is an organism that makes its own food
from the primary energy source an example is photosynthetic plants that make their own food
from sunlight (using a process called photosynthesis) and chemosynthetic bacteria that make
their food energy from chemicals in hydrothermal vents. These are called autotrophs or primary
producers.
Next come organisms that eat the autotrophs; these organisms are called herbivores or
primary consumers -- an example is a rabbit that eats grass. The next link in the chain is animals
that eat herbivores - these are called secondary consumers -- an example is a snake that eats
rabbits. In turn, these animals are eaten by larger predators -- an example is an owl that eats
snakes. The tertiary consumers are are eaten by quaternary consumers -- an example is a hawk
that eats owls. Each food chain ends with a top predator and animal with no natural enemies (like
an alligator, hawk, or polar bear).
The arrows in a food chain show the flow of energy, from the sun or hydrothermal vent to
a top predator. As the energy flows from organism to organism, energy is lost at each step. A
network of many food chains is called a food web.
When any organism dies, it is eventually eaten by detrivores (like vultures, worms and
crabs) and broken down by decomposers (mostly bacteria and fungi), and the exchange of energy
continues.
There are mainly two types of food chains operating in nature.
a) Grazing food chain
Grazing food chain is generally seen in ecosystems such as grassland, pond or lake
Characteristics of Grazing Food Chain
a) These are directly dependent upon solar radiations as the primary source of energy and the
producers (green plants) synthesize their plant biomass by the process of photosynthesis.
Producers form the first trophic level.
b) Herbivores or primary consumers eat upon the producers and form the second trophic level.
c) Herbivores are in-turn eaten by different categories of carnivores forming the higher trophic
levels.
d) Grazing food chains are longer food chains and they always end at decomposer level.
b) Detritus food chain.
Detritus food chain, as seen in a forest ecosystem, wherein the dominant primary consumers
(herbivores) are the insects, which usually consume less than ten percent of the net primary
production. The major remaining portion of more than 90% is consumed later as dead plant
material by small detritus feeding organisms such as micro arthropods, oligochaetes and
microorganisms.
The detritus feeding organisms process the detritus in their gut by reducing it into small pieces,
digesting it partially or completely, thus making organic material available for bacterial or fungal
attack. These microorganisms also act as food for many soil animals.
This food chain is decomposer organism based and is called 'detritus or decomposer food chain'.
Characteristics of Detritus Food Chain
a) Primary source of energy is dead organic matter called 'detritus' which are fallen leaves, plant
parts or dead animal bodies.
b) Primary consumers are 'detritivores' including protozoans, bacteria, fungi, etc which feed upon
the detritus saprophytically.
c) Detritivores are inturn eaten by secondary consumers such as insect larvae, nematodes, etc.
d) Detritus food chains are generally shorter than grazing food chains
e) In nature, detritus food chains are indispensable as the dead organic matter of grazing food
chain is acted upon by the detritivores to recycle the inorganic elements into the ecosystem.
Detritus food chain
Detritus
Detritivores
Detritivores Consumers
Small
Carnivores
Large
Carnivores
Mangrove
Fallen Leaves
and Dead
Bodies
Fungi,Bacteria
and Protozoans
Insect Larvae,Certain
Crustaceans,Molluscs and
Fishes
Minnows
Small game
fish etc.
Large
Fish,Fish
eating Birds
Differences between Grazing and Detritus food Chains
Characters
Grazing food
Detritus food chain
chain
Primary source of Solar
energy
radiations
Detritus
First trophic level All herbivores
Size
Long-sized
chains
Detritivores (a mixed group in terms of trophic levels and
may be herbivores, omnivores and primary carnivores)
Small-sized chains
Significance of Food Chains
Food chain studies help,
a) understanding the feeding relationships and the interaction between organisms in any
ecosystem.
b) comprehend the energy flow mechanism and matter circulation in ecosystems.
c) understand the movement of toxic substances and the problem of 'Biological magnification' in
the ecosystem.
d) analyse the biological diversity in an ecosystem.