Phy Geo (Unit 4-Topic 1) Food Web and Food Chain & Major Biomes of the World

Physical Geography (Topic 1-Unit 4)

 Food Web and Food Chain

The living community of plants and animals in any area together with the non-living components of the environment such as soil, air and water, constitute the ecosystem.

Every living organism is in some way dependent on other organisms. Plants are food for herbivorous animals which are in turn food for carnivorous animals. Thus there are different tropic levels in the ecosystem.

The transfer of energy from the source in plants through a series of organisms by eating and\being eaten constitutes food chains. At each transfer, a large proportion of energy is lost in the form of heat. Hence green plants occupy the first level, herbivores the second level, carnivores the third level and secondary carnivores the fourth level.

Food chains show one producer being eaten by one consumer and perhaps another consumer eating the first consumer. Food chains are not that simple in real ecosystems. Producers are usually eaten by many different consumers, and most consumers are eaten by more than one predator. For example, a squirrel eats several different types of seeds, fruits, and nuts. The squirrel may be eaten by a fox, a hawk, or a raccoon. The raccoon also feeds on frogs, clams, birds’ eggs, and corn. The fox will also eat mice and grasshoppers; the hawk will also eat frogs, mice, and snakes. Most organisms are part of several food chains. A model that shows the connections between several different food chains is called a food web.

In a food chain, energy is lost in each step of the chain in two forms: first by the organism producing heat and doing work, and second, by the food that is not completely digested or absorbed. Therefore, the food web depends on a constant supply of energy from producers and nutrients that are recycled by the decomposition of organisms. As food is passed along the food chain, only about 10% of the energy is transferred to the next level. For example, 10% of the energy phytoplankton received from the sun can be used by zooplankton at the next level. From one level to the next about 90% of the energy used by the previous level is lost. This means that there has to be a lot more organisms at the lower levels than at the upper levels. The number of organisms at each level makes a pyramid shape and is called a food pyramid.

Food chain refers to a linked feeding series in an ecosystem. A food chain illustrates the order in which a chain of organisms feed upon each other and the  sequence of organisms through which energy and materials are transferred, in the form of food, from one tropic level to another. The following graphics shows a simple food chain.

The food chains are not isolated and are inter-linked to each other. For example, a Hawk can eat snakes as well as other smaller birds. A mouse can eat grass, bread or even grasshoppers. A Lizard can eat insects of different types. Thus, various food chains are intertwined in each other making a food web. A Foodweb is thus a system of interlocking and interdependent food chains. A typical Foodweb is shown in the below graphics.
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Major Biomes of the World

Vegetation comprises of plants growing over the surface of the earth. The plant geographers have divided the vegetation of the world into four great biochores :

The Forest Biochore : Defined as plant formation consisting of trees growing close together  nd forming a layer of foliage that shades the ground.

The Savanna Biochore : It is a combination of trees and grasslands.

The Grassland Biochore : An upland vegetation of herbs which include grasses or grasslike plants and herbs. 

The Desert Biochore : It is associated with arid climate and thinly dispersed plants. According to varied climate and density of vegetation cover, the vegetation of world is divided into three types.

1. Forests Forests are classified on the basis of coverage, density and greenery.

(a) Tropical Rainforests : These are known as equatorial forests and found in Amazon Basin, Zaire Basin and other wetter areas  in the monsoon regions. These are broad-leaved hardwoods composed of trees like Mahogany, Rubber, Cinchona, etc.

(b) Monsoon Forests : These are found in areas having 100 to 200 cm of rainfall. They are hardwood forests and generally deciduous.

(c) Coniferous Forests : These are evergreen, needlelike softwood forests found in North America and South America.

2. GrasslandsGrasslands are characterized by less rainfall.

(a) Savannas : These are tropical grasslands, occuring as a transitional belt between  hot desert and monsoon regions and are areas of thick high grasses. These are known by different names like Parkland in Africa, Illonos in Venezuela, Campos in Brazil and Downs in Australia.

(b) Steppes : These are short, shallow rooted grasses growing in bunches. These are found in low latitudes and middle latitudes. These are reduced to weedy plants due to overgrazing.

(c) Prairies : These are temperate grasslands. The grasses are tall and deep rooted. These are found in Southern Russia, Central Europe and Argentina. The original vegetation in these regions is destroyed and the land turned into agricultural land.

(d) Meadows : These are grasslands maintained artificially and known as pastures; common in England and North Kalahari desert.

3. Desert Shrubs Desert shrubs consist of bushy plants in hot sandy deserts and mosses in cold tundras. These occur in parts of Atacama desert in South America.