1.   Second, the hemlocks are the keystone of a unique ecosystem.

2.   The goal of ManateeLab is to educate the public about the endangered Florida manatee and the unique ecosystem upon which it depends.

3.   This was a colossal mistake that destroyed a unique ecosystem.

4.   When specialists discuss the environmental hazards of the trans-Caspian oil pipeline, they cite two main factors that might seriously harm the unique Caspian ecosystem.

5.   The trees began to grow to normal heights and the unique ecosystem was threatened.