Imagine that you are an ecologist who must determine whether an entire river and lake biome is being threatened by human activity. what might you look for in an indicator species? a. one that has been introduced to the biome. b. one that lives off of the biome's water-loving trees. c. one that is most easily affected by changes in water quality. d. one that you are most familiar with, and for which you can judge health by appearance of fur or other outward indicators

The answer is c. One that is most easily affected by changes in water quality.

An indicator species is a biological species whose presence or absence and even abundance can indicate specific environmental conditions. For example, there are some species (plant, fish, invertebrates,...) that can live only in an extremely clean river. But, if that clean river gets polluted by human activity, the river will not be any long extremely clean, and sensitive species will not survive and will disappear from the river. Its absence will indicate that river quality is threatened.