Ecotone is

1. a polluted area

2. the bottom of a lake

3. a zone of transition between two communities

4. a zone of developing community

(c) The adjacent biotic (natural) communities, generally do not possess a fine demarcation edge or line between them. The adjacent of two communities is represented by the population of both the communities and this transition zone between two communities is referred to as an ecotone. The rest of the options do not define ecotone (zone of transition)