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Problem : What is the difference between geographical isolation by vicariance and by dispersal?

The difference between isolation by vicariance and dispersal is when the geographical barrier appeared relative to the distribution of the populations. Isolation by vicariance occurs when a population that is already widely distributed is divided by the appearance of a barrier. Dispersal occurs when part of a population crosses a barrier that already exists.

Problem : A farmer plants two crops of the same plant three weeks apart. The first crop each crop flowers for about a week, approximately four weeks after planting. What type of reproductive isolation would you expect to find between these two populations?

These two populations will be temporally isolated. If each crop flowers for only a week and they were planted three weeks apart, the first crop will stop flowering a full week before the second crop starts to flower.

Problem : The male of a given species of frog uses distinctive calls to attract mates. Two populations of these frogs coexist in a single pond but never interbreed because their mating calls are different. Females of one population will not respond to the calls of a male of the other populations. What type of reproductive isolation is this?

This is an example of behavioral isolation. The two species cannot interbreed because their calls, a type of courtship behavior, are different.

Problem : Describe gametic isolation.

In gametic isolation, no physical or behavioral barriers to mating exist. Members of two different species mate, but do not produce offspring because their gametes are unable to fuse to form a zygote.