Yet in the absence of reasoned guidelines, decisions are made by default, with a small percentage of species — often those that serve commercial interests or are popular with the public — receiving the bulk of money. In 2013, the latest year for which figures are available, more than $10 million in state and federal money was devoted to the grizzly bear, and more than $34 million to the upper Columbia spring run Chinook salmon.

In contrast, $214 was spent on the desert slender salamander and $400 on the Alabama cavefish.

Despite their differences, conservationists from the older and newer schools have some common ground. They agree, for example, that some species may need protection under the Endangered Species Act for many decades, if not permanently, and that efforts to protect a species or an ecosystem should begin much earlier than they do now to improve the chances of succeeding.

They also share a history that includes an equally heated debate that took place more than 100 years ago between John Muir and Gifford Pinchot.

Muir, the founder of the Sierra Club, argued that nature should be preserved for its own sake and protected from human intruders. Pinchot, the first head of the Forest Service, saw humans as stewards of nature, entitled to use land for agriculture, logging and grazing as long as they did so wisely.

The two views, some environmental scientists said, need not be contradictory, even in their modern form.

“I don’t see why it’s a problem to talk on several levels about the importance of conserving nature,” said Taylor Ricketts, the director of the Gund Institute for Ecological Economics at the University of Vermont and a founder of the Natural Capital Project. He added, “The big mistake has been to frame this as a choice.”