Tangled Branches of the Evolutionary Tree

I’ve always looked at the world through species-centric beer goggles

By Rob Breeding

While the Clean Air and Clean Water acts have their fans, I view the Endangered Species Act as the most consequential piece of legislation passed in those halcyon days of the 1970s when the environment was a nonpartisan issue. Republican President Richard Nixon signed all three into law.

It’s not that I don’t think clean air and water are important, but I’ve always looked at the world through species-centric beer goggles. Species and diversity are just my starting point.

I long had a somewhat simplistic definition of a species. A horse was a species, as was a donkey. The two animals could mate, producing maybe the greatest of all domesticated animals, the mule. Since that hybrid offspring is infertile, however, the horse and the mule couldn’t be the same species.

That was fine until I started writing about wildlife conservation. I recall the time a biologist in Arizona patiently walked me through the complexities. Animals that had been isolated through time — whether by geographic barriers or those of habit and behavior — may retain the ability to produce fertile offspring. Still, in terms of biology and the ESA, they were unique and separate species.

Cutthroat and rainbow trout illustrate the point. These are separate species, but much to the chagrin of fisheries managers, these fish readily breed and produce fertile offspring. In some Montana rivers such as the Bitterroot, cuttbow hybrids dominate.

The process that created the unique, and now threatened westslope cutthroat, was one of geographic isolation. In his classic “Native Trout of Western North America,” biologist and author Robert Behnke explained that the westslope came first when an ancient cutthroat swam up the Columbia River system and evolved into the fish we know today. The rainbow evolved from a later arrival, after barrier falls had blocked upstream passage for the newcomers.

There remain examples where cutthroat and rainbow exist side-by-side in the wild, without hybridizing one species or the other out of existence. The coastal sea-run cutthroat is a rare fish, but it’s continued existence means the fish’s habitats are distinct enough from its rainbow cousin that they rarely find themselves occupying the same spawning redd. It’s that, or perhaps the oddball hybrid loses some critical instinct needed to survive, and these costal cuttbows succumb to the environment.

Grizzly and polar bears are another example as they produce sexually viable offspring. Hybrids in the wild are rare since polar bears spend most of their time out on the sea ice, while grizzly bears tend to stay on land. Some speculate that as warming reduces the extent and duration of sea ice, polar bears will increasingly be driven into grizzly habitat and naturally occurring “pizzly” bears will be more common.

Similar forces may be what created the controversial red wolf subspecies of the eastern United States. DNA evidence has led some researchers to conclude that this species is actually a wolf-coyote hybrid. We know there was some intermingling of the two species in the 20th century as coyotes spread east into red wolf habitat. DNA evidence however, suggests this mingling of wolf-coyote DNA can be traced back further in time than the western migration of coyotes.

As important a tool as the ESA has become, it’s a reminder that this species-centric viewpoint has its limitations. If the fertile legislative environment of the 1970s had created an Endangered Ecosystem Act as well, we might not fuss so much about whether a wolf was exactly the right wolf, and instead focus on the important role apex predators play maintaining balance in healthy ecosystems.

In other words, focus on species and how they interact with other species and their environment, rather than just saving a single endangered animal and calling it good.

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