Final answer:
Biological evolution and species differentiation are illustrated by changes in populations due to environmental pressures and mating preferences, leading to shifts in physical characteristics and an increase in certain traits over others.
Step-by-step explanation:
The question posed is related to biological concepts, specifically the adaptation and genetic variability within species and how environmental pressures can lead to changes in a population's characteristics.
The data that would provide compelling evidence that two populations of nocturnal toads represent different species would likely include genetic differences, differences in mating calls, or other behavioral or physiological characteristics that prevent interbreeding.
In the case of the hypothetical beetle population, the most likely change due to the environmental pressure of pollution darkening the tree trunks would be an increase in darker-colored beetles, as these would be better camouflaged against predators. Graphs depicting these changes in populations over time would show these shifts in characteristics. Lastly, if there was a preference shift in female fish from bright colors to size, we would expect the population to evolve accordingly with larger fish becoming more prevalent over time.