Ecotone is
a. The transitional area between two communities
b. Interaction between two populations
c. Development of ecads
d. Development of ecotypes

Hint: It is the process of change occurring within the two social groups of individuals depending upon their geographical area.

Complete answer:
An ecotone is a transitional area between two biological communities. It is an area where two communities meet and combine. This integration depends upon the type of communities that undergo transition.

Additional information:
1. The term ecotone was derived from the combination of two words ‘ecology plus tone', the term ecotone was derived from the Greek word tonos or tension, meaning a place where ecologies are in tension.
2. The transition may be narrow or wide depending upon the type of community.
3. If the transition is local it may occur between a field and a forest.
4. If the transition occurs is regional then it may occur between a forest and a grassland ecosystem.
5. Ecotones are the sharp boundary lines that separate the two communities in an area.
6. An ecotone may form due to the changes in the physical environment.
7. It consists of highly adaptable species that can colonize in transitional areas.
8. Ecotones are sometimes associated with ecoline as a physical transition zone between two systems.

So, the correct answer is the ‘Transitional area between two communities’.

Note: An ecoline is an area of slow but continuous change that occurs from one ecosystem to another. In between the two ecosystems, there is no sharp boundary and occurs across the environmental gradient. It is a variation of the physicochemical environment which depends on one or two physicochemical factors of life, and presence or absence of certain species.