background extinction

[ băkground′ ]

The ongoing extinction of individual species due to environmental or ecological factors such as climate change, disease, loss of habitat, or competitive disadvantage in relation to other species. Background extinction occurs at a fairly steady rate over geological time and is the result of normal evolutionary processes, with only a limited number of species in an ecosystem being affected at any one time. Compare mass extinction.

QUIZZES

WHO SAID IT: A QUIZ ON PRESIDENTIAL WIT AND WISDOM

Think you know your presidents? Take this quiz and see if you can match the style, wit, and ideology of these memorable lines to the right POTUS.
Question 1 of 9
“I do believe that the buck stops here, that I cannot rely upon public opinion polls to tell me what is right. I do believe that right makes might and that if I am wrong, 10 angels swearing I was right would make no difference.”
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.