Frogs and Natural Selection

A population of frogs live in an environment where the vegetation is gray and dull due to a lack of rainfall. The frogs in the population have skin that is either gray or green. They have adhesive pads on their toes to help them climb trees and plants to find food and avoid predators. Owls, snakes, and raccoons are a few of the predators that hunt the frogs in the environment. The frogs eat many different kinds of insects and small invertebrates. The environment undergoes a change. An increasing amount of rainfall causes the vegetation in the area to become more green and vibrant. Scientists observe the frog population in the area over several generations after the change. The graph shows their observations.

The bar graph titled Frog Populations shows the percentage of the population of frogs along the vertical axis, from 0 to 100, in increments of 10. Along the horizontal-axis, four generations of green and gray frogs are shown titled Generation 1, Generation 2, Generation 3, and Generation 4. For Generation 1, gray frogs were more than 80% of the population, while green frogs were less than 20%. For Generation 2, gray frogs were 70% of the population, while green frogs were 30%. For Generation 3, gray frogs were 60% of the population, while green frogs were 40%. For Generation 4, gray frogs were less than 40% of the population, while green frogs were more than 60%.

Constructed Response Question
Describe the change to the population of gray frogs over the generations. Provide an explanation for the change.

1 answer

Over the observed generations, there has been a significant decline in the population of gray frogs and a corresponding increase in the population of green frogs. In Generation 1, gray frogs made up more than 80% of the population, while green frogs constituted less than 20%. By Generation 2, the percentage of gray frogs decreased to 70%, and this downward trend continued into Generation 3, where they represented 60% of the population. In Generation 4, gray frogs accounted for less than 40%, while green frogs increased to more than 60% of the population.

The change in the population of gray frogs can be attributed to natural selection driven by the change in the environment. Initially, when vegetation was gray and dull, gray frogs had a camouflage advantage, which helped them avoid predators such as owls, snakes, and raccoons. However, with the increase in rainfall, the vegetation transitioned to a greener and more vibrant state. In this new environment, the green frogs had a camouflage advantage over the gray frogs, making them more difficult for predators to spot.

As a result, the green frogs experienced higher survival rates and reproductive success, leading to their population increase over the generations. In contrast, the gray frogs, being less camouflaged against the now green landscape, became more susceptible to predation, resulting in their decline. This illustrates the principles of natural selection, where environmental changes can favor certain traits that enhance survival and reproduction, ultimately leading to shifts in population dynamics over time.