18 



Tlie ecological niche is ;i particular cou'ibiiialioii 

 of physical factors (inicrohabitat) and biotic rela- 

 tions (role) re(|uire(l by a species for the normal 

 course of its life activities. 



The term and concept was first developed by 

 Joseph Grinnell (1917. 1924, 1928) of California. 

 He considered the ecological niche the ultimate dis- 

 tributional or spatial unit occu])ied by just one species, 

 or subs])ecies, to which that species is held by struc- 

 tural and instinctive limitations such as climatic fac- 

 tors, kind and amount of food, suitable nesting-sites, 

 and cover. He recognized the close relation between 

 animal distribution and cover, and he spoke of ani- 

 mals generally and birds in particular as having prej- 

 erencc for a particular niche, choosing surroundings 

 consistent with their needs. At about the same time, 

 the Englishman Charles Elton (1927) independently 

 defined the niche in more functional terms as an 

 animal's place in the biotic environment, its relation 

 to jood and enemies. The present-day concept of the 

 niche is an elaboration of these basic ideas, with em- 

 phasis on the relation of the organism -to both the 

 physical and biotic factors of its environment. The 

 restriction of a species to a particular niche depends 

 on its structural adaptations, physiological adjust- 

 ments, and developed behavior patterns. 



In many respects, the species in its niche is the 

 only finite unit of animal distribution ; at least the 

 relationship is the one most subject to objective and 

 concrete definition. The concept of niche in the hier- 

 archy of ecological distributional units is more or less 

 equivalent to the concept of species in the hierarchy 

 of taxonomic units. When we begin to group niches 

 into the higher units of habitat, biocies, biociation, 

 biome, and realm we become as increasingly vague 

 and arbitrary as we are when classifying species into 

 genera, families, orders, classes, and phyla. 



Ecological Processes 



and Community 



Dynamics: 



Niche Segregation 



CHARACTERISTICS OF THE NICHE 



Microhabitat 



The physical features of substratum, space, 

 and microclimate are basic determinants of whether 

 a particular niche can be occupied by a given species. 

 The basic differences in marine, fresh-water, and ter- 

 restrial habitats restricting the distribution of com- 

 munities is immediately obvious. The features differ- 

 entiating microhabitats are less apparent, but assume 

 major significance when particular occupants of it, 

 rather than the community as such, are under investi- 

 gation (Prosser 1935). 



The intimate relation between niche segregation, 

 substratum, and microclimate is well shown in the 

 distribution of four species of ants in a pine forest of 



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