CONCEPT OF ECOLOGICAL NICHE

1. Spatial/ Habitat Niche   (The Concept of Grinell):

• It was first defined by Grinell in 1904. 

• According to Grinell, niche corresponded to habitat. 

• It concerns the physical space occupied by an organism. 

• Eg. the Distribution of seven species of millipedes in the forest floor of maple oak forest. 

2. Tropic Niche (The Concept of Odum):

• Definition of the niche was given by Odum in 1971.

•  It is concerned with the trophic position of an organism. 

• Eg. Occurance of various species of birds in Galapagos island. 

• Odum had stated that the habitat of an individual represents an address, the ecological

niche a profession. However, under the term of the profession

3. Hypervolumic Niche(The concept of Hutchinson) 

• Hutchinson combined the idea of habitats and function.

• His concept of ecological niche is based on multidimensional hypervolume (n-dimensional), 

• where the dimensions are environmental conditions and resources, which describe the

requirements of an individual or a species to practice their way of life, particularly,

for their population to persist. 

• The "hypervolume defines the multi-dimensional space of resources (eg, light, nutrients,

structure, etc.) available to(and used by) organisms,

4.  FUNDAMENTAL NICHE AND REALIZED NICHE: This term was first coined by Joseph Grinnell in 1917 

• Fundamental Niche: fundamental niche of a species by testing the range of conditions in

which it grows and reproduces in the absence of competitors 

• Realized Niche: Range of Environmental conditions in which a species is really found.

It is a smaller portion of the fundamental niche that is actually filled. They can be tolerated

narrow range.

• Sometimes fundamental niche and realized niche is termed as pre-competitive and

post-competitive niches,

•  Realized niche for different populations of same species may also vary, because

of differences in competitors and predators between locations

• Fundamental Niche>Realized Niche (inhibition/Competition)

•  Fundamental Niche = Realized Niche (Tolerance)

• FundamentalNiche  < Realized Niche (Facillation/Symbiosis)

Ecological Equivalents: Species that use similar niches in different habitats or locations.

Guilds: Group of species with the comparable role and niche dimensions within a community.

5.  NICHE WIDTH

• The concept of niche width or niche breadth refers fundamentally to the diversity of resource

use shown by anyone organism or group of organisms.

• The organisms/species whose resources use is restricted to a small portion of the

available resource spectrum are known to have narrow niches, whereas those who

exploit a relatively diverse set of resources within the resource continuum are defined

with broad niches.

• Specialist and generalist are relative terms that describe the endpoints of continuous

variation in the degree of specialization in resource use, behavior, and physiology.

• Specialist species have narrow niches and high efficiency of niche utilization.

• Generalist species have broad niches and low efficiency of niche utilization.

Levin (1996) measure of niche breadth/Width is

 Breadth/Width = B = 1/𝚺pi2

Where, pi= proportion of individuals that use resource

 i, or the proportion of diet of each individual composed of i.

 Because pi is in the denominator, species that use many resources will have a higher value of

B, reflecting a generalist pattern of resource use.

6.  NICHE OVERLAP/SIMILARITY

• Niche overlap measures are used to assess the similarity in resource use by two species.

• The degree and type of niche overlap can be used to examine the interspecific competition.

• 

1. If niches overlap, and resources are limiting, then competition occurs.

2. Adjoining niches are an (indirect) indication that competition may have lead to niche

divergence in the past.