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Invasive species

Invasive species: A type of plant, animal, or other organism that does not naturally live in a certain area but has been introduced there, often by people. An invasive species can spread quickly, especially if it has no natural predators in its new home. An invasive species can hurt native species, disrupt ecosystems, and create problems for people (for example, weeds and insects that damage crops).

Indicator

Indicator: a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time, a signal for attracting attention, (chemistry) a substance that changes color to indicate the presence of some ion or substance; can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction.