Barriers & Animal distribution # Zoology 3rd Semester#Unit ll

A possible isolating mechanism (e.g. physical , biological , ecological,etc.) which prevents the dispersion or spreading of living organisms on earth is considered as a barrier .

Types of barriers:

(1) Extrinsic barriers: The barriers which works from outside of an individual's body of population are extrinsic .

  These are of three types : Physiographic , Biotic & Climatic .

Physiographic barriers : Several natural , physical and geographical phenomenon act as barriers and result in irregular and discontinuous animal distribution on the earth .e.g. large water bodies, large land mass , desert , forest , mountain ranges, ice mass, atmospheric pressure, etc.

e.g. (a) Dense forest of Mexico prevented the distribution of elephants (Elephas & Mastodons ) from North America to South America during Pleistocene period .

(b) Heterosomata is deep sea dweller and never come up due to low pressure .

Biotic barriers: A large no of organisms are food specific , hence, food is considered as a barrier (e.g. red panda, giant panda , etc). Similarly , host- parasite relation , predator-prey relationships  and inter - specific competition are also act as barriers .

Climatic barriers : Temperature, rainfall, solar radiation ,photoperiodism etc. also play major role in animal distribution .

(2) Intrinsic barriers:

When nature and behaviour of an animal act as barriers , then considered as intrinsic barriers . These are of four types :

Philopatry : A few animals e.g. Rovanda bird ( Zosterpos rendovae) withstand all climate in its native area and never moves.

Homing instinct : Due to this instinct most animals always return back to native area .

Parental care: A long period of parental care made the youngs to be habitated  to their mother's land .

Habitat & Nitche also act as intrinsic barriers of animal distribution over the earth .

Geographical isolation is a common factor of speciation , hence, a barrier is treated  as a key factor of speciation as both of these are inter-related .

                         A few QA

(1) What are catadromous migration  and anadromous migration ?

Generally , fresh water fish and marine fish live in their respective habitat ,but, a few exceptional migration are there:

(i) Byne fish , eel fish etc. are fresh-water fish , but, during breeding time migrate to saline water , hence, catadromous .

(ii) Hilsa, sad,salmon ,etc. are marine fishes and during breeding season they migrate to fresh/sweet water from sea, hence, anadromous.

(2) What are hydrocoles, merocoles and xerocoles ?

Hyrocoles=water loving organisms.

Merocoles=organisms living in places with neither excess nor less water .

Xerocoles= organisms living in dry areas .

Important Questions

(1) What is barrier?                  2/2016

(2).   Discuss on different types of barriers which animal distribution.  5/2016,2018(

(3)Stete the role of barrier in discontinous distribution of animals .     3/2016

(4) SN...Physical barrier      5/2017