All of the given are assumptions made for Hardy-Weinberg equilibrium except "mutations are non-lethal." In the Hardy-Weinberg model, there is an assumption of no mutations, as mutations would introduce new alleles that would distort the ratios predicted for a population in Hardy-Weinberg equilibrium. 

The correct answer is "sympatric." Speciation often occurs after a group of individuals becomes geographically isolated from its original population, as occurs in allopatric and peripatric specition. In parapatric speciation, there is a very small overlap in the area of the diverging population during and after speciation. In sympatric speciation, a new species evolves without the individuals ever leaving the area of the ancestral species. "Convergent" is a type of evolution where two different species adapt similar phenotypes.

The definition of species states that once two groups of animals are no longer able to breed with one another, they are considered members of different species. Allopatric speciation describes speciation that happens when two groups of organisms become separated by a geographic barrier that prevents interbreeding. In this question, the river is the geographic barrier separating the organisms in the mountains from those in the forest. Over time, these two groups of organisms acquire differences. Once these differences are enough to prevent the members of these two groups from being able to mate with one another, they are considered different species and allopatric speciation has occurred. 

A bat's wing and a bird's wing are analogous structures, as the development of these structures does not share an evolutionary history. The common ancestor of bats and birds did not have wings, therefore these traits arose independently. Therefore, they are not homologous, but represent convergent evolution, as similar traits arose from different lineages due to environmental pressures.

Mutation, migration, natural selection, and genetic drift all change the presence and proportion of alleles in a given population, contributing to evolution. An unchanging environment would not contribute to changes in alleles and, therefore, does not contribute to evolution.

We see natural selection because those chickens that are entirely immune to the disease produce more offspring than those chickens who were infected but survive. The gene(s) that offers protection against contracting the disease is retained at a greater rate than the gene(s) that protects the chicken from dying of the disease. If the genetic diversity of the population is reduced generations later, this suggests that the chickens experienced a population bottleneck when the population number dropped to half of its original number.

The founder effect is when genetic variability is lost due to a small number of individuals from a larger population forming a new population. The smaller population only breeds with each other and is not genetically representative of the larger group from which it was founded. Thus, the humans on a deserted island are an example of this. The hurricane might be an example of a population bottle neck and the breeder might be causing a population bottleneck by only breeding certain dogs, but the humans are a better example of the deliberate formation of a new breeding population.

In order for animals to belong to the same species, they must, by definition, be able to mate with one another to produce viable offspring. The question stem says that these two animals cannot mate to produce viable offspring; therefore, they cannot belong to the same species. Since they cannot belong to the same species, they cannot "represent closely related variants of the same species," either. Although they are not the same species, the information about their similar anatomy and diet suggests that they likely evolved from a common ancestor, making the answer choice "The two animals are adapted to live in completely different environments" also incorrect.

An organism's evolutionary fitness is defined by the number of offspring that it produces. Mutations that increase the number of offspring that an organism can have will, by definition, increase its evolutionary fitness. Evolutionary fitness is not defined by strength, size, or habitat. While it is theoretically possible that each of the wrong answers might increase the fitness of an organism in the right circumstances, none of the wrong answers are guaranteed to increase the number of offspring produced by the organism.