| Whitebark pines are what silviculturists term a keystone species of upper subalpine ecosystems. |
| Aldicarb, aldrin, chlordane, DDT, dieldrin, lindane, mirex, PCBs, and toxaphene are present in all our country's ecosystems, animals, and humans. |
| A keystone species in several ecosystems, the grizzly was listed in 1975 as threatened in the lower 48 states. |
| The reality is that we are rapaciously destroying ecosystems and burning fossil fuels as if there were no tomorrow. |
| The invasion of alien tree species has seriously impacted many natural forest ecosystems around the world. |
| This means that organisms are not agglomerates but ecosystems of co-acting cells with a unique functional focus. |
