Question

- What are ecological pyramids and how are used to predict the change in populations over time?

- What is biomagnification and how does it occur?

Answer 1

Ecological pyramid is a graphic representation that shows the relationship between organisms at various trophic levels in a food chain. The ecological pyramids are of three types. They are

1. Pyramid of energy

2. Pyramid of biomass

3. Pyramid of numbers

Pyramid of energy  is a type of pyramid that represents the flow of energy from the producers to the final consumers. It is always upright.

Pyramid of biomass represents the amount of biomass of the organisms present at each trophic level. Biomass is nothing but the weight of the organisms.

Pyramid of numbers is constructed based on the number of organisms in each trophic level. As we go up the levels of the pyramid, the number of organisms decreases. The producers are present in large numbers so they are placed at the bottom of pyramid.

  In general, all ecological pyramids are upright, but in certain cases the pyramid of numbers is not upright eg.detritus food chain. It is because many organisms feed on one dead plant or animal. The pyramid of biomass in an ocean is also inverted. But pyramid of energy is always upright because the flow of energy is always unidirectional.

Organisms in an ecosystem can be divided in to trophic levels. Producers are the base of the ecosystem. They are usually plants, but it can be any organism that can make their own food, like some bacteria. Primary consumers are herbivores that eat the producers. Secondary consumers eat the primary consumers. Tertiary consumers are called top predators, that eat both the primary and secondary consumers.

When all the populations are in balance, the ecosystem is at equilibrium. But, altering just one population may produce catastrophic effects on the ecosystem and homeostasis.Producers form the base of the food web. Recently, deforestation has become problem.Without the producers, there is less food for the primary consumers. Without the primary consumers, secondary consumers have less food. With fewer secondary consumers, the top predators,won't have enough food. This is called a population crash, is a common occurrence with man-made disturbances in the ecosystem.

  Even secondary consumers are important in a food web. Example for a secondary consumer is sea otter. The sea otter is a keystone species(essential for maintaining balance in an ecosystem). The sea otter eats sea urchins. Without this control on the sea urchin population, they grow out of control in a population boom, eating all the kelp and causing a population crash. Thus pyramids can also be used to predict change in population over time.

2. Biomagnification is the increase of contaminated substances or toxic chemicals in food chains. These substances often present in contaminated environments. This substances include heavy metals like mercury, arsenic, pesticides such as DDT, and polychlorinated biphenyls (PCBs) compounds which are then taken up by organisms because of the food they consume.

The concentration of these toxic chemicals and pollutants is very low when released in different environments, it is then accumulates and gets absorbed by lower organisms in the food chains such as fish, earthworms, and plants. When the lower organisms are eaten by other organism and the process goes up and these organisms starts to accumulate toxic materials inside the body. They can accumulate more chemicals than lower organisms of the food chain as a result, biomagnifiaction occurs.