In evolutionary terms, “fitness” refers to the reproductive success or reproductive potential of an organism—its contribution to its species' gene pool.

Batesian mimicry involves a harmless species mimicking an unpalatable or harmful species, such as the butterfly in the example. Mullerian mimicry involves two unpalatable or harmful species resembling each other. This also helps predators learn which types of species to avoid. Cryptic coloration is more simply known as camouflage. Aposematic coloration is warning coloration, such as bright colors on poisonous tree frogs or venomous snakes. 

According to Darwin's theory, the survival and reproduction of individuals is not random. Survival and reproduction is tied to the variations among individuals. Those with the most favorable variations are more fit; therefore, they are naturally selected.

In order for natural selection to take place, members of a population must have different biological fitnesses (a measure of how likely it is that an individual will pass on its genes through reproduction). Different biological fitnesses are a result of different phenotypes. Organisms with phenotypes better suited to their environments will have a higher fitness. 

Natural selection does not require sexual dimorphism or competition between populations. Adaptation to environmental niches can result from natural selection over time.

Initially, the population of bacteria was composed of mostly bacteria vulnerable to methicillin and a small number of resistant bacteria. Treatment with methicillin destroyed all of the vulnerable bacteria. leaving only the resistant alive to reproduce. Over time, the resistant bacteria became the majority.

Although it's possible a new patient could have introduced the first resistant bacteria, it's unlikely to have occurred in such a short time frame. 

It's also unlikely the bacteria possessed the ability to resist the bacteria from the start, as methicillin treatment wouldn't have worked on any of them.

Bacteria do not possess a mechanism by which they can build up immunity to antibiotics over time.

A sharp decrease in population size caused by environmental or human impact is known as the bottleneck effect, where the bottlenecking occurs in the relative population diversity. This is mainly due to the fact that the individuals who survived rarely represent the genetic makeup of the initial population as a whole. The effect size is a statistical measurement of the strength of a phenomenon, which can be applied in the study of population dynamics, but is not a type of genetic drift. Artificial selection is the deliberate selection of mating preferences by humans in order to alter the proportion of traits in the offspring. However, this type of selection is not caused by a dramatic event, nor does it result in a severe decrease in population size. The founder effect does pertain to small populations but specifically on how genetic variation is lost in a small population that comes from a larger population due to misrepresentation. 

This would be equivalent to the number of “grandchildren” produced by the organism. Biological fitness is defined by how capable the organism is of increasing the frequency of its own alleles. While individuals that consume more food grow larger, or have more mates than other members of their species are clearly thriving in their environment, which does not always mean that they produce more offspring. Also, it is possible that an organism could produce a large number of offspring that are infertile, which would ultimately not increase the frequency of its alleles. Therefore, the best determination of an organism’s fitness is the production of offspring that are themselves able to successfully produce offspring.

Selection pressures is the correct answer here. A selection pressure is any factor that affects fertility or mortality, or anything that can cause a population to change genetically.

Breeding with genetically different individuals tends to "scramble" the alleles of a population. When genetically similar individuals breed, they tend to produce homozygous genotypes in their offspring, so potentially dangerous recessive alleles appear more frequently and beneficial alleles are not as efficiently selected for. Thus, inbred populations have a lower survival rate over time. This is called inbreeding depression.

Each of the above is true, but the predictive power of evolution lies in its ability to form testable hypotheses. Natural selection and descent with modification can be most visibly observed in bacterial populations, where new generations can arise in as little as forty minutes. Biologists in every field form hypotheses based on how a mechanism, organism, or process is adaptive to its environment.