The Endangered Species Act of 1973 (ESA) provides for both the
conservation and protection of plant and animal species that
face the threat of extinction as well as for "the ecosystems
upon which they depend." Species must be endangered or
threatened throughout a significant portion of their range. The
ESA replaced the Endangered Species Conservation Act of 1969;
the ESA has been amended several times. Why Do We Need An
Endangered Species Act?Fossil records show that in the distant
past animals and plants have had finite lifetimes. In the 20th
century, scientists became concerned about the loss of common
animals and plants. Ecologists believe that we are living in an
era of rapid species extinctions that are being triggered by
human action, such as over-harvesting and habitat degradation
(including pollution and climate change). The Act reflected a
change in scientific thinking because it envisioned nature as a
series of ecosystems; in order to protect a species, we have to
think "bigger" than just that speci