The bottleneck effect occurs when a random and catastrophic event reduces the population of an organism by a large number. The remaining individuals repopulate the area after the event, but the genetic diversity of the population is greatly reduced. The founder effect occurs when a group of individuals are separated from the main population and subsequently establish a new population. This new population's genetic diversity is also greatly reduced.  In both cases a small number of individual establish a population and this small "pool" of genes is how genetic diversity is reduced. The wolves are separated from their pack by being released in a new area and then established a new population; this is an example of the founder effect. The pea plants were killed by a random event, but the survivors did not survive by random chance. Instead they had a gene that gave them higher fitness compared to the other members. This is a better example of natural selection. The fish in the flash flood were separated from the main population and subsequently established a new population in the nearby lake. This is an example of the founder effect. The drought lake is the best example of the Bottleneck effect because the event was random and the survivors lived due to random chance. A small number of the fish reestablished their population in the lake, their genetic diversity was also reduced.

Genetic drift is a change in allele frequency between generations due to sampling error. Since genetic drift makes certain allele variations disappear, it decreases genetic variation. Additionally, genetic drift has a smaller effect in larger populations and a large effect in small populations.

Gene flow is a mechanism of evolution in which genes are transferred between populations. Two examples of gene flow are migration and horizontal gene transfer. In the case of migration, the movement of individuals into or out of a population also results in a transfer of alleles. Horizontal gene transfer (common in bacteria) is the transfer of genes through means other than reproduction (i.e. plasmid exchange).

Genetic drift is due to the production of a finite number of zygotes within a population. This causes allele frequencies to change from one generation to the next. Genetic drift can result in the reduction of the fitness of individuals within a population if the alleles passed on are deleterious.

When a population is reduced for a short period of time, only the rarest alleles are usually lost, as is seen in bottlenecking. In order for a significant change in allelic frequency to be seen, the population must become significantly small, and it must stay small for a significant amount of time. The latter is referred to as the Founder Effect.

This is an example of gene flow, because a small number of individuals from one population are passing some genes on to those in another population. Genetic drift occurs within a single population, so it does not apply here. This is not an example of speciation. There can't be a prezygotic barrier present if the geese are able to successfully mate.

Temporal isolation is between populations due to barriers related to time, such as differences in mating periods or differences in the time of day that individuals are most active. Geographic isolation between populations is due to physical barriers, not time. It wouldn't be both of them because only temporal isolation deals with time, versus geographic isolation is based on the physical barrier between populations such as mountains, rivers, or, for example, insects living on different trees in the jungle. Reproductive isolation is the inability to interbreed between species for various reasons like sterile offspring, physical incompatibility, or different mating rituals.

Genetic drift occurs when the frequency of alleles in a population change by random chance. Change in allele frequency based on biological fitness is natural selection, not genetic drift. The change in allele frequency due to members moving from one population to another describes migration. A brand new allele that did not exist in the parents is the result of mutation.

The Bottleneck effect happens when an event occurs that drastically reduces the population of a species. The remaining individuals most likely do not represent the genetics of the population before the catastrophic event, since it becomes a much smaller sample size.