Ecological Pyramid 
Answer of Ecological Pyramid

    We can compare the tropic levels in a food chain using ecological pyramids.

Pyramid of numbers
anwer of Pyramid of number

A pyramid of numbers allows as to compare the number of organisms present in each trophic level at a particular time.

How can we construct  a pyramid of number ?
Answer of pyramid of number

Let us suppose that there are 10 hawks in a given area, and each hawk needs to feed on 1 snake every day.In 1 month the 10 hawks will need  300 snakes to keep them alive.If each snake eats 1 rabbit every 2 days, 300 snakes will need 4500 rabbits in 1 month.If each rabbit eats about 20 grass plants every day, 4500 rabbits will need about 2700000 greass plants in one month.The number of organisms at each trophic level can be used to construct a pyramid of numbers.For this food chain, the pyramid will be broad at the base and narrow towards the top.

Pyramid of  biomass

A pyramid of biomass allows us to compare the mass of organisms present in each trophic level a particular time.

The pyramid of biomass is constructed based on the dry mass of organisms in each trophic level at any one time.This is called the standing mass of organisms.

How can we contruct a pyramid of biomass ?? ( Ecological Pyramid )

Consider the food chain.Let us suppose that there are 1000 rabbits in a given area at one time we can determine the biomass of rabbits in a given area at one time as follows;

1.Dry 10 rabbits in a given area at 100 C until a construct mass is obtained.Let us say the dry mass of the rabbit is A g.The biomass of 1000 rabbits is therefore 100 A g.

2.Repeat step 1 for all the other trophic levels.

3.Construct a pyramid of biomass using the information obtained in step 1 and 2

For the food chain we have just considered, the pyramid of biomass has a similar shape of that pyramid of numbers.All the grasses together have a large biomass than the rabbits.All the rabbits together have a large biomass than the snakes.All the snakes together have a large biomass than the hawks.

Variations in ecological pyramids

Most ecological pyramids are pyramid-shaped, bu there are important exceptions.

1. Pyramid of numbers may be upside down or inverted if;

> Organisms of one trophic level are parasitic on organisms of another trophic level.

> Many small organisms of one trophic level feed on a large organisms of another trophic level.Consider the following food chain.

 Tree > aphid > protozoa

In this case , the pyramid of numbers is inverted.The bottom of the pyramid is represented by only one tree.Many aphids are parasitic on  the tree and many protozoa are parasitic on the aphids.

However, the pyramid of biomass remains broad at the bottom and narrow towards the apex.This is because one tree has a comparatively large biomass to support the other populations.

2. Pyramids of biomass for rapidly reproducing organisms are also not pyramid shaped.Since the pyramid of biomass based on standing mass , it does not take into account the rate of reproduction of organisms.This is a disadvantages when considering organisms that reproduce rapidly.Consider the following food chain;

                                Phytoplankron > Zooplankton > Small fish > Large fish

Phytoplankton are microscopic plant like organisms that can make food by photosynthesis.Zooplankton are microscopic primary consumers that feed on phytoplankon.The pyramid gives the impression that the biomass of phytoplankton is smaller than that of zooplankton, which is not possible.What happens is that rate of reproduction of phytoplankton is fast enough to replace the organisms that were eaten by zooplankton.

Pyramid of Energy ( Ecological Pyramid )

The total energy in the various trophic levels of a food chain can be represented in the form of a pyramid.This is called a pyramid of energy.

Unlike the pyramid of biomass, we need to determine the energy content in each trophic level over a period of time, say one year.This means we have to take into consideration the rate at which organisms in each trophic level reproduce.The average energy content of each trophic level can then be calculated using special techniques.Knowing the energy content in each trophic level we can construct a pyramid of energy.

The pyramid of energy is thus constructed based on the total energy level in each trophic level over a certain period of time, for example, one year.

A lot of energy is lost to the envioronment as food is transferred from one trophic level to the next.Energy may be lost to the environment;

1. as heat during respiration at every trophic level;

2. in uneaten body part;

3. through undigested matter egested by consumers; and

4. through waste products excreted by consumers for example urea

Heat energy is wasted energy since it cannot be recycled in any way in the ecosystem.

More and more energy is lost as we go down a food chain.The total  energy is highest at the first trophic level and lowest at the last trophic level and lowest at the last trophic level.Hence a pyramid of energy is always broad at the base and narrow towards the top.A large number of producers may be required to support just a few consumers at the end of a food chain.

Pyramid of biomass ( Ecological Pyramid )

1. Related to the biomass of organisms

2. Constructed based on the biomass at any give time.

3. Does not consider the rate of reproduction of organisms.

Pyramid of energy  ( Ecological Pyramid )

1. Related to the energy content of organisms.

2. Constructed based on energy content over a period of time.

3.Takes into consideration the rate of reproduction of organisms.

Short food chain are more efficient in every transfer ( Ecological Pyramid )

Since energy is lost at each trophic level , less and less energy is available for the organism at the next level as we go down the food chain.Hence , food chains are generally short.A shorter food chain means more energy is lost to the environment.We say that shorter food chains are more efficient than long food chains.For example , more energy will be available to a man if he feeds directly on crop plants grown in a given area , rather than eating the cattle that feed on his crop plants.

Key Ideas ( Ecological Pyramid ) means related to Pyramid ( Ecological Pyramid )

1. We can study the trophic level in food chains using ecological pyramids.

2. A pyramid of numbers allows us to compare the number of organisms present in each trophic level at a particular time.

3. A pyramid of biomass allows us to compare the dry mass of organisms present in each trophic level at a particular time.

4. A pyramid of energy allows us to compare the total energy in each trophic level over a period of time for example one year.

5. Energy is lost as heat energy at each trophic level.Heat energy cannot be recycled in any way in an ecosystems.A food chain is usually short because of the loss of energy at the each trophic level.