Historic Update VII

Civil strife in Guatemala accelerated in the 1980s, making it unsafe for the American scientist to stay and monitor the grebe population.  In 1982, the only game warden patrolling the lake was murdered.  By 1984, about 20 percent of the original reed beds remained.  The population update for the giant grebe looked like this:

1980:  130
1982:  80
1985:  56

Finally, the grebes disappear.

1989:  4
1991:  None could be found

It's possible that the presence of the pied-billed grebe in the same lake influenced the loss of the giant grebe by interbreeding with it.

The bass population still exists; black bass is a standard feature on local restaurant menus.  Its initial large population could not be sustained, however.  For the local residents, the fish now most often eaten is bluegill.

Questions

1. Hypothetically, a population of two (male and female) can keep a species alive. Realistically, however, a small population size presents a survival risk.  Why?
2. How could we determine whether the pied-billed grebe "swamped" the giant grebe with its genes?
3. Why didn't the bass population succeed in the lake?

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