Ecological Succession, Food Chain, Food Web, Ecological pyramids

Ecological Succession

Primary succession

Primary succession is one of two types of biological and ecological succession of plant life, occurring in an environment in which new substrate devoid of vegetation and other organisms usually lacking soil, such as a lava flow or area left from retreated glacier, is deposited.

• From a pioneer community (initiation) to a climax community (Final)
• Rare & takes a long time to generate.

Secondary succession

• Development of a community which forms after the existing natural vegetation that constitutes a community is removed, disturbed or destroyed by a natural event like hurricane or forest fire or by human related events like tilling or harvesting land.
• A secondary succession is relatively fast as, the soil has the necessary nutrients as well as a large pool of seeds and other dormant stages of organisms.

 Food Chain

• Plants are eaten by insects, which are eaten by frogs; these frogs are eaten by fish, which are eaten by human beings. This sequence is known as Food chain.
• Plant > insect > frog > fish > human
• Each step in the food chain is called a “Trophic level” as in above food chain – 5 tropic levels

Type of food Chain

• Grazing: Starts with green plants e.g., Grass > Grasshoppers > Birds > Snakes > Hawks
• Parasitic: Also starts with green plants but here smaller organisms depending on larger organism g. Grass > cow > lice
• Detritus*/saprophytic: Starts with dead plant/animal/ waste material > decomposers

*Detritus = dry leaves, dead plant, animal remains, dead skin cells, other organic waste (urine, excreta)

Trophic level

• Trophic level to which an organism belongs, indicates how far it is away from plants in the food chain
• Energy Flow in food chain is unidirectional, means energy flow can never be from carnivores to herbivores or herbivores to producers
• In grazing food chain, primary source of energy is living plant biomass while in detritus food chain, source of energy is dead organic matter or detritus

Energy Flow in the Ecosystem

• When energy is passed from one tropic level to next trophic level, some part of energy is wasted, So energy declines as we move up in the chain/ web / pyramid in :

• Body heat (Metabolism) + Respiration + Capturing the prey
• Remains trapped in skin, hair, bone and teeth of a prey, however this energy is later utilized when scavenger (hyena) comes into picture, as Hyena’s stomach acid is so powerful, it can digest the skin, hair, bone, teeth and other remnants of a prey corpse

• Generally, only 1/10^th of the energy passes to next tropic level

Food Web

Food chain assumes the isolated linear line. But in real life, frog could be eating other insects apart from grasshopper. Fish could be eating smaller fishes apart from frog. So there exists an interconnected Network of (Food Chain + Food Chain + Food chain…). This interconnected network of food chains is known as food web.

Bio-accumulation

• Refers how pollutant enters a food chain means concentration of pollutant from the environment to the first organism in a food chain.
• Occurs when an organism absorbs a toxic substance at a rate greater than that at which he can digest

Bio-magnification

• Increase of toxic chemicals conc. up the food chain
• a man-induced process
• occurs with mobile & non-degradable chemicals / fat soluble pollutants only
• DDT concentration

Biotic Potential

• Unlimited food + ideal environmental conditions [arr] A species can produce offspring at maximum rate, known as Biotic potential
• Can be high or low, depending on how many offspring can a species produce in ideal conditions.

Ecological pyramids 

Ecological pyramids represent the trophic structure or trophic function of the ecosystem and and is mainly of 3 types:

Pyramid of Number

• Depicts the number of individual organisms at different trophic levels of food chain
• May be inverted or upright or spindle shaped

Pyramid of Biomass

• Depicts total dry weight of all organisms at each tropic level at a particular time, measured in g/m2
• May be upright or inverted

Pyramid of Energy

• a graphic representation of the amount of energy trapped per unit time and area in different trophic level of a food chain with producers forming the base and the top carnivores at the tip
• Always upright