Some species are called indicator speciesbecause the loss of a population of such a species serves as an early warning of problems arising from pollution  Environmentalists tracking the effects of pollution have increasingly paid heed to indicator species; yet environmentalists would be misguided if they attributed the loss of a population to pollution in all cases  Though declines in population often do signal environmental degradation, they are just as often a result of the natural evolution of an ecosystem
We must remember that, in nature, change is the status quo
Environmentalists' use of indicator species in tracking the effects of pollution is often problematic.