Power
Every once in a while you hear about a real estate developer threatening to "go medieval on" some pointy-headed environmentalist who's holding up the construction of a dam, or something. That pointy-headed environmentalist has power. The pointy-head is an ecologist type who can halt construction with her knowledge of and fervor for nature.
Then again, there are always the ecologists who actually work for those construction and engineering firms, investigating sites for environmental worthiness. You may be surprised to hear that, often, those ecologists find far fewer problems with potential construction sites. Go figure.
Whether working for the trees or the little green slips of paper they sometimes turn into, one thing's for sure: ecologists have the power to shape the world.