Concept of Habitat & Ecological Niche

{Habitat & Ecological Niche}

“The habitat of an Organism is the place where it lives, or the place where one would go to find it.” Habitat is also defined as

“The sum total of environmental factors of an individual, population or community in locality.” Thus, the habitat of the water “backswimmer” Notonecta is the swallow vegetation-choked areas (Littoral Zone) of ponds & lakes; that is where one would go to collect this particular organism.

Habitat commonly refers to a large area or the place occupied by entire community. E.g.: - Pond, Lake, River, Estuary, Ocean, Forest, Desert, Grassland, Wood-land etc. Like the habitat of the sand sage grassland community is the series of sandy soil occurring along the north sides of rivers in the Southern Great Plains region of the United States.

However, it may be as smaller as a Burrow, Bark of tree or intestine of an Ant.

On the other hand “Ecological Niche, is a more inclusive term that includes not only the physical space occupied by an organism but also its functional role in the community (e.g.: - its trophic position) and its position in environmental gradients of temperature, moisture, pH, Soil and other condition of existence.” Grinnel (1971) used term Niche.

These three aspects of the ecological niche can be conveniently designated as the: -

      1. Spatial or Habitat Niche: It refers to the Physical Space occupied by an organism. E.g. Distribution of seven species of Millipedes in forest floor of a Maple Oak forest (O’Neill, 1971).

      2. Trophic Niche: It deals with the trophic position of an organism.

E.g. Notonecta & Corixa live in the same aquatic habitat i.e. Pond, but are of different trophic niche. Notonecta is a Predator while Corixa feeds largely on decaying vegetation.

      3. Multidimensional or Hyper volume niche: It’s considered as “abstract n-dimensional inhabitant hype volume (By G.E.Hutchinson, 1965).

Consequently, the ecological niche of an organism depends not only on where it lives but also on what it does (how it transforms energy, behaves, responds to and modifies its physical & biotic environment) & how it is constrained by other species.

By analogy, Ecologist E.P.Odum said that “the Habitat is the organism’s address and the Niche is its Profession.”

Ecological Pyramids

 “An Ecological Pyramid is a graphic representation of an Ecological Parameter, like no. of   individuals present in various trophic levels of a food chain with producers forming the base & top   carnivores, the tip.”

Ecological Pyramids were developed by ‘Charles Eiton’ (1927) & are therefore, also called ‘Eiton Pyramids’. In a pyramid the various steps of food chain are represented sequence-wise.

An Ecological Pyramid can be upright, inverted & spindle shaped (narrow, both at base & tip with broader part in the middle). There are three types of Ecological Pyramid:-

      1) Pyramid of Numbers: -

     “It is graphic representation of the no. of individuals per unit area of various trophic levels stepwise   with producers being kept at the base & top carnivores kept at the tip.” In most cases pyramid of   Number is upright.

   

       2) Pyramid of Biomass: - The amount of living or organic matter present in an organism is called ‘Biomass’. It is measured, both as fresh and dry weight.

“Pyramid of Biomass is a graphic representation of biomass present sequence wise per unit area of   different trophic levels with producers at the base & top carnivores kept at the tip.”

 Pyramid of Biomass is more real than the Pyramid of Numbers because latter doesn’t take   consideration the size of individual. E.g. Mouse, Squirrel, Rabbit, Deer & Antelope.

Pyramid of Biomass is upright for terrestrial habitats. Inverted or Spindle-shaped pyramid for aquatic habitats. However, if total biomass produced per unit time is calculated, the pyramid of biomass shall always be upright.

 3)   Pyramid of Energy: -

“It is a graphic representation of amount of energy trapped per unit time & area in different trophic   levels of a food chain with producers forming the base & top carnivores the tip.”

Maximum energy content is present in producers. As the energy passes in to higher trophic levels      along with food, its amount decreases because of its dissipation as heat & use in overcoming  entropy as well as for performing various body activities.

Thus Pyramid of Energy is always upright. It is more accurate than the Pyramid of Biomass or  the  Pyramid of Numbers.

Food Web: A Network of Food Chains

“It is a network of food chains which become inter-connected at various trophic levels so as to form a number of feeding connections amongst the different organisms of a biotic community.”

Food Web is meant for increasing the stability of an ecosystem by providing alternate source of food and allowing the endangered population to grow in size. Normally a food web operates according to taste and food preferences of the organisms at each trophic level. 

However, availability of food source and other compulsions are equally important.

Example-> In Sunderbans, the tigers eats fish and crab in the absence of their natural preys.

Some organisms normally operate at more than on trophic level. Thus Human beings are not only herbivores but also carnivores at various levels. Jackals are both carnivores and scavengers. Snake feed on mice (herbivores) as well as frogs (carnivores). 

Therefore, the concept of Food Web appears more real ecologically than the concept of a simple Food Chain.

Food Chain

   

“The transfer of food energy from the producers, through a series of organisms (herbivores to carnivores to decomposers) with repeated eating & being eaten, is known as Food Chain.” It includes:-

1) Primary Consumers or Herbivores:  They are animals which feed on plants or plant products.

Eg. grasshoppers and several other insects, rabbit. Hare, deer, antelope, elephant, zooplankton etc.

Herbivores are also called key industry animals because they convert plant matter in to animal matter.

2) Secondary Consumers or primary Carnivores: They ingest or prey upon herbivores animals.

Eg. Frog, predator, Insects, several Birds, Fishes, Wild Cat, Fox, Jackal (also Scavenger) etc.

3) Tertiary Consumers or Secondary Carnivores: They are larger carnivores which prey upon primary carnivores.

Eg. Wolf (feeds on fox), Snake (Prey upon frog).

4) Top Carnivores: They are the last order consumers or carnivores which are not preyed upon by other animals because of their size, agility & ferociousness,

Eg. Shark, Crocodile, Eagle, Peacock, Tiger, Lion.

Some common food chains are:-

**Land:

a) Grass-->Grass Hoppers-->Frog-Snakes-->Peacock/Falcon

b) Vegetation-->Rabbit-->Fox-->Wolf-->Tiger

**Aquatic:

a) Phytoplankton-->Zooplankton-->Small Crustaceans-->Predator Insects-->         Small Fish-->Larger Fish-->Crocodile

In Nature we distinguish two general types of Food Chains:

1) Grazing Food Chain: - This type of food chain starts from the living green plants goes to grazing herbivores & on to carnivores. It is directly dependent on influx of solar radiation.

2) Detritus Food Chain: - This type of food chain goes from dead organic matter to microorganisms & then to organisms feeding on detritus & their predators. Such ecosystems are less dependent on direct solar energy.

Ecology-“The Study of Structure & Function of Nature”

“Ecology word is combination of two Greek words “Oikos (home, house or dwelling place) & Logos (the study of).” This describes relation of organisms & their surroundings (environment).

When we go much deeper in understandings of Nature, broadly, we find two important aspects i.e. organisms and its surroundings (environment). Which, mutually co-related and dependent on each other with much complex relation.

Time to time many scientist used and coined different terminologies to study Nature.

French zoologist Isodore Geoffroy st.Hilaire in 1859 had coined the term “Ethology” for “Study of the relations of the organisms within the family & society in the aggregate & in community.”

Charles Darwin in his book “On the Origin of Species” (1859) has used several potential terms, which can be used in explanation of Modern Ecology in broader way.

In 1886 Haeckel used the term Ecology as “the knowledge of the sum of the relations of organisms to the surroundings outer world to organic & inorganic condition of existence.”

R Mishra (1967) described Ecology as “Interactions of form, functions & factors.” These three factors combinedely construct the triangle of Nature.

Odum in 1969 define Ecology as “the study of structure & function of Nature.

Krebs (1985) has defined Ecology as “Ecology is the scientific study of the interactions that determine the distribution & abundance of organisms.”

In more recent updates, the terminology “Biotic (Living) & Abiotic (non-living) used in describing the Ecology as its component and both are related with each other & functions accordingly as a proper system.