Allopatric Speciation ,Sympatric Speciation

(1) Allopetric Speciation .

    Speciation means the formation of new species . If a polulation of a species is seperated by extrinsic Physiographic or Geographical Barriers into two or more populations and over time the organisms adapt themselves in the new environment and if there is no any gene flow between these newly isolated populations then the organisms will never breed to each other in future ,  thus new species generated and  the phenomenon is termed as the     Allopatric Speciation  and the newly formed species are called Allopetric.

  It means the geographic isolation is turned into reproductive isolation to make allopatric species .

    Types:

Allopetric Seciation are of two types :

# Vicariant speciation: When a large & widely distributed population is splitted into different populations due to any kind of extrinsic barriers , or if a group migrated into a far place and the intermediate members became extinct due to change of temperature or other factors  then the distribution turned to discontinous  and over time seperated goups emerged as new species , then the process is called vicariant speciation.

  e.g.

,During the Pliocene Isthmus emerged at Panama and many marine animals forced to be Pacific and Caribbean populations.

#Peripatric Speciation :

   When a few members of a very large and wide spread population got seperated and perform rapid gene exchange / genetic drift in the localised population  and there is no any gene exchange with the main body  then  over time this small divergent group will turn into a new species . Such a  speciation is termed as the   peripatric or the founder-effect .

      So, here genetic drift if followed by natural selection to make it reproductively isolated .

e.g. Petrocia multicolour (robin ) ,

       Tanysiptera galeata 

Sympatric Speciation

   When a group of members of a randomly mating population made them isolated reproductively by reducing gene flow and over time evolved as a new species even  though there was no any geographical barriers  and both of the species share the same geographical area , then such a speciation method is called as Sympetric speciation .

     Evidence 

   Apple maggot fly / Rhagoletis pomonella  is today represented by two races :

Race I : Hawthorn fly 

Race ll: Apple fly

Hawthorn fruit plant is native to America  and once the ancestor fly laid eggs in the fruit , but after the introduction of apple in America a group of flies started to lay eggs on apple , over 200 yrs they achived reproductive isolation and turned to a new species even though both species share the same geographical area and will operate Gause's law or competitive exclusion principle in future .