air and water pollution are directly responsible for the loss of some species. in their studies of these pollution effects, biologists have determined that are especially sensitive to air pollution, and are now being used as an index of urban air quality. air and water pollution are directly responsible for the loss of some species. in their studies of these pollution effects, biologists have determined that are especially sensitive to air pollution, and are now being used as an index of urban air quality. evergreen trees lichens deciduous trees warblers songbirds