The Founder Effect is due to a sampling error. By taking a small sample of an existing population and creating a new population, there is zero probability that the new population will have all of the same alleles as the old population. Therefore, the alleles of the new population are likely to differ from the original population. 

The three key requirements for natural selection are variation, differential reproduction, and heredity. That is, there must be variation in the population, and that variation must affect the mating success of some individuals (differential reproduction). Organisms who successfully mate must be able to pass on their genes to their offspring (heredity).

Gene flow refers to movement of alleles between populations, and is not necessary for natural selection to occur.

Because the males croak loudly when females approach, this behavior is suggestive of sexual selection. It is likely the males are demonstrating for the females in an effort to attract a mate. Sexual selection occurs when one sex (usually females) choose a mate based on a trait that does not directly affect survival (here, the frog's croak). There is not enough information to determine if the selection is stabilizing, directional, or neither. Territorial selection is not one of the types of a natural selection.

It is incorrect to think of natural selection as a response to a "need." Natural selection will select among variants in a population, resulting in evolution. Individuals and populations cannot influence the course of natural selection based on wants or needs.

Convergent evolution is the development of characteristics in unrelated species, resulting from adaptations to similar environmental conditions whereas the other choices identify other variations of evolution. Divergent evolution is the loss of similar structures in related species due to different environmental conditions. Speciation is the process by which new species evolve as a result of environmental conditions. Genetic drift is the change in allele frequencies within a population due to the imperfections of random sampling techniques. Coevolution is the phenomenon characterized by the evolution of two organisms simultaneously as a result of their interaction with each other. 

A type of natural selection in which genetic diversity decreases as the population stabilizes with respect to a particular trait value is stabilizing selection. In this mode of natural selection, the "average" phenotype is selected for and its proportion in the population increases over time. Directional selection is a type of natural selection in which a polarized phenotype is selected for over the other phenotypes, causing a shift toward the extremes with respect to proportion of individuals with that phenotype. Diversifying selection is another type of natural selection in which both extremes of a phenotype are selected for, causing an increase in the proportion of those alleles in the population. Nonspontaneous selection is not a type of natural selection.

Stabilizing selection favors the intermediate phenotypes in a population while disruptive selection favors extreme phenotypes. Artificial selection is frequently practiced by humans in breeding livestock, pets, and crops. Sexual selection is dependent on interaction between males and females within a population. Domestic selection is not a real term.

Quantifiable traits, like beak size, in a population tend to form a bell curve when graphed. Selection that leads to more individuals on either end of the graph compared to individuals in the center is disruptive, and in this case leads to a lack of medium sized birds since birds with either small or large beaks were favored. Selection that favors individuals on one side of the graph is directional, and selection that favors individuals in the center of the graph is stabilizing.

Disruptive selection happens when the environment favors individuals on the extreme ends of a phenotype.

Directional selection favors individuals on one end of a phenotype (for example, a different environment may only favor black beetles, but not white or gray).

Stabilizing selection favors against extreme phenotypes (for example, a different environment may favor gray beetles, but not black or white beetles). 

Mitosis does not create genetic variation. The primary roles of mitosis are growth and healing.

Crossing over refers to the exchange of genetic material between chromosomes during metaphase I of meiosis, and is largely responsible for enhancing the genetic variation of eukaryotes. Mutation is necessary to introduce new genetic factors and adaptations into a population, thus furthering evolution and promoting variation.