What characterizes indicator species in an ecosystem?

Indicator species are organisms whose presence, absence, or abundance reflects a specific environmental condition, particularly the health of an ecosystem. These species are typically sensitive to changes in their environment, especially those related to pollution levels. Their reaction to pollutants makes them valuable for assessing the ecological state of an area; for example, a decline in the population of a certain sensitive species may signal a degradation of environmental quality due to increased pollution.

The sensitivity of indicator species allows scientists to monitor environmental changes, as these species can serve as early warning signs for broader ecological problems. This is why option C—species that are sensitive to pollution—is the correct characterization of indicator species.

In this context, other options do not accurately define indicator species. While some species might thrive in polluted environments or exhibit resilience to climate change, these characteristics are not indicative of the specific role that indicator species play in ecosystem health assessment. Similarly, indicator species are not necessarily always abundant; their populations can fluctuate significantly based on environmental conditions, particularly pollution levels that they are sensitive to.