In death valley, california, there are several ponds that are formed in various areas of the desert. each pond contains its own species of fish unique to the pond it lives in.

geographic isolation

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.