2. Ecological isolation:
Lack of interbreeding between populations that occupy distinct habitats within same general area is called ecological isolation. White throated sparrow frequents dense thickets, whereas white crowned sparrow inhabits fields and meadows, and seldom penetrates far into dense growth. Two species may coexist within a few hundred yards of one another, yet seldom meet during breeding season.
In case of 750 species of fig wasp, each species of fig wasp breeds in fruits of a particular species of fig and each fig species hosts only one species of pollinating wasp. Ecological isolation may slow down interbreeding, but may not prevent gene flow entirely. Other mechanism also contributes to inter-specific isolation between two or more species.
When two species occupy similar habitats but cannot mate due to different breeding seasons, then it is called temporal (time-related) isolation. Hawthorn- liking and apple-liking fruit files are also partially isolated from one another because they emerge from their host fruits and breed at slightly different time of year.
Different signals and behaviours create behavioural isolation. Striking colours and calls of male songbirds may attract females of their own species, while females of other species treat them with utmost indifference. Among frogs, males often impressively indiscriminate, jumping in every female in sight, regardless of species, when spirit moves them. Females, however, approach only male frogs that croak the Ribbet appropriate to their species. If they do find themselves in an unwanted embrace, they utter, “release call”, which causes the male to let go. As a result, few hybrids are produced.