How does a population experience variation in traits? A.
through an increased birth rate

B.
through a decreased death rate

C.
through mutations and genetic recombination

D.
through the introduction of an invasive species

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.

the sphincter muscles at the end of the digestive tract is the anus.

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.