Non-native organisms brought into a region, habitat, or ECOSYSTEM by human activity.

Works containing information articles on subjects in every field of knowledge, usually arranged in alphabetical order, or a similar work limited to a special field or subject. (From The ALA Glossary of Library and Information Science, 1983)

The protection, preservation, restoration, and rational use of all resources in the total environment.

A functional system which includes the organisms of a natural community together with their environment. (McGraw Hill Dictionary of Scientific and Technical Terms, 4th ed)

NATIONAL LIBRARY OF MEDICINE service for health professionals and consumers. It links extensive information from the National Institutes of Health and other reviewed sources of information on specific diseases and conditions.

The variety of all native living organisms and their various forms and interrelationships.

Sudden increase in the incidence of a disease. The concept includes EPIDEMICS and PANDEMICS.