Fill-in the blank: A is a species that provides a sign, or indication, of the quality of the ecosystem’s environmental conditions. Group of answer choices

keystone species

indicator species

invasive species

introduced species

indicator species. One that is sensitive to changes in conditions that may lead to disruption of the ecology of a habitat.

Explanation: a keystone species is one whose disappearance will severely disrupt the ecology of a habitat. An example is the cassowary, which is essential for the distribution of rainforest tree seeds in north Queensland, Australia

Invasive species are those that compete successfully and replace species native to a habitat, often because of lack of predators or in response to habitat change.

Introduced species are those that are transported outside their natural distribution, generally by humans, deliberately or accidentally. Such species are often invasive. An introduced species which is also invasive is the cane toad, Rhinella marina, that is continuing to expand its range across north-eastern Australia.

An indicator species is one sensitive to small disturbances of the ecology, giving a warning of possible problems. An example is the weed Plantago coronopus which is sensitive to increasing soil salinity and responds by its leaves developing a red tinge. Increasing salinity is a problem in many areas of inland Australia.