PLEASE,PLEASE HELP ME..What is a deme in terms of evolution?...THIS IS VERY VERY IMPORTANT!

Question

please help me.i require a definition of a deme in terms of EVOLUTION,not just a normal definition for a deme which i know already.the definition i have for a deme from my biology teacher is that a deme is defined as a genetically isolated population,that is,a group of organisms of the same species that are unable to interbreed with other members of the same species.I DO NOT UNDERSTAND WHAT THIS MEANS AT-ALL because this definition is conflicting with the definition of a species,which is a group of organisms which look alike and can interbreed to produce fertile offspring! if you can give me a better DEFINITION with a SIMPLE explanation i would appreciate it....i am willing to give the maximum amount of points for a proper definition and a proper explanation...please i have searched Wikipedia already and i know the definition they give there already,and it is rather vague.so if you know your biology and can give help me here i would really appreciate it...thank you very much.

Answer 1

Think of a Deme as a starting point for creating a new species. If a population becomes reproductively isolated, there is no longer gene flow between this population and the rest of the population as a whole. So, any new mutations that crop up in the isolated population will not move to the rest of the population. Likewise any mutations that occur in the non-isolated population will not be found in the isolated group. For example:

Lets say there are several populations of mice, defined as groups A, B, C, D and E. We will say that group E is isolated, but members of the other groups can move from group to group. If a new mutation occurs in group A, it may eventually spread to B, C, and D because these populations are not isolated. Group E is isolated so there is no way for individuals carrying the mutation to mate with members of group E and bring the mutation to that population.

Over time, if the reproductive barrier continues, more and more genetic differences will occur between the non-isolated groups (A,B,C,D) and the isolated group (E). Given enough generations and different environmental pressures, it is likely that E will diverge as a separate species.

Hope this helps.