Understanding Trophic Levels, Food Chains, and Ecological Pyramids in Ecosystems

1. RAHUL MALAKAR ASST. PROFESSOR DEPT. OF BOTANY MANGALDAI COLLEGE

2. Concept of trophic level in an ecosystem (Greek word ‘trophic’ = to food or feeding) A trophic level refers to the position of an organism in the food chain. The number of trophic levels is equal to the number of steps in the food chain. The green plants (producers) occupying the first trophic level (T1) are called producers. The energy produced by the producers is utilized by the plant eaters (herbivores) they are called primary consumers and occupy the second trophic level (T2). Herbivores are eaten by carnivores, which occupy the third trophic level (T3). They are also called secondary consumers or primary carnivores. Carnivores are eaten by the other carnivores, which occupy the fourth trophic level (T4). They are called the tertiary consumers or secondary carnivores. Some organisms which eat both plants and animals are called as omnivores (Crow). Such organisms may occupy more than one trophic level in the food chain.

3. FOOD CHAIN The sequence of eating and being eaten in an ecosystem is known as food chain. e.g. in grassland ecosystem, in forest ecosystem,

4. Two types of food cains – a) Grazing food chain b) Detritus food chain a) Grazing food chain: It starts with green plants, its primary producers and terminates in carnivores. The grazing food chain derive its energy basically from green plants. They are found only in natural ecosystem. e.g. In pond ecosystem, Phytoplankton Zoo plankton Small fish Carnivorous fish

5. b) Detritus food chain: It starts with death organic matters which are consumed by the detrivores and decomposers. Partially decompose death organic matters and even the decomposers are consumed by detrivores and their predators. Detritus food chains obtain energy, primarily from plant biomass and secondarily from microbial biomass and tertiarilly from carnivores.

6. e.g. In mangrove or esturine ecosystem, Leaf litters Saprotrophs + Small carnivorous fish Large carnivorous fish Small algae Detrivores ( crabs, insect larva, nematode, small fishes)

7. FOOD WEB Food web is a network of food chains, where different types of organisms are connected at different trophic levels so that there are number of options of eating and being eaten at each trophic level.

8. ❖Significance of food chain and food web: a) Food chains and food webs play a very significant role in the ecosystem because the two most important functions of energy flow and nutrient cycling take place through them. b) Food chain also helps in maintaining and regulating the population size of different animals and thus helps in maintaining the ecological balance. c) Food chain shows a unique property of biological magnification of some chemicals.

9. d) Food web is constructed to describe species interaction called direct interaction. e) Food web can be used to illustrate indirect interactions among different species. f) Food can be used to study bottom-up or top down control of community structure. g) Food web can be used to reveal different patterns of energy transfer in terrestrial and aquatic ecosystems.

10. ECOLOGICAL PYRAMID The graphical representation of trophic structure and function of an ecosystem starting with producers at the base and successive trophic levels forming the apex is known as ecological pyramids. There are 3 types of ecological pyramids: a) Pyramid of Number b) Pyramid of Biomass c) Pyramid of Energy

11. a) Pyramid of Number: It represents the number of individual organisms at each trophic level. Depending upon the types of ecosystem and food chains pyramids of number are of two types – 1. Upright pyramid 2. Inverted pyramid Grassland ecosystem and pond ecosystem show upright pyramid of number.

12. Upright pyramid of number in grassland ecosystem Upright pyramid of number in pond ecosystem

13. The pyramid of number in forest ecosystem looks spindle shaped.

14. The pyramid of number in a parasite ecosystem is always inverted .

15. b) Pyramid of Biomass: A graphical representation of the amount of organic material (biomass) present at each successive trophic level in an ecosystem is called pyramid of biomass. It is based upon the total biomass each trophic level in a food chain. It can be upright or inverted.

16. Grassland and forest ecosystems show upright pyramids of biomass.

17. The pyramid of biomass for pond ecosystem is always inverted in shape.

18. c) Pyramid of Energy: A graphical representation of energy flow at each successive trophic level in an ecosystem is called pyramid of energy. The bottom of the pyramid of energy is occupied by the producers. There is a gradual decrease in energy transfer at successive tropic levels from producers to the upper levels. Therefore, the pyramid of energy is always upright.

19. Pyramid of energy