Keystone Kismet

Wolves were driven out of Yellowstone National Park a hundred years ago. Then in 1995, a few were reintroduced. The beneficial impact from their return has been astounding – beyond what anyone expected or hoped.

This 4.5-minute video explains it better than I could, with the added perks of some adorbs intro and outro howling, plus the narrator’s pronunciation of quintuple to rhyme with scruple:

TL;DR: Wolves have kept elks on the move, which has allowed trees and shrubs to grow back, which has provided food and habitat for other animals while stabilizing river banks. Beavers have resumed building dams, which has created yet more habitat. All manner of native animal and plant species are now repopulating the park. Those wolves have transformed the Yellowstone ecosystem as well as its physical geography.

As this story illustrates, wolves are a keystone species, meaning they have a disproportionate impact on their natural environment relative to their abundance. Keystones can be predators (e.g., wolves), prey (Antarctic krill), ecosystem engineers (beavers), mutualists (oxpecker birds and the rhinos whose parasites they eat), or even plants.

Oxpeckers on you-know-who’s back. "Red-billed oxpecker" by peianwu is licensed under CC BY-ND 2.0.

Keystone plants provide a critical source of food and/or shelter for other species. Entomologist Doug Tallamy and his colleagues have demonstrated that native plants are far better than non-natives in their ability to sustain caterpillars, which are in turn a foundational food group for most terrestrial songbirds in North America. What they’ve also shown is that some native plants outperform even their native cousins by orders of magnitude. Some native trees, for example, host hundreds of caterpillar species each, while others support only a few or none. Wherever they looked, Tallamy et al observed that about five percent of the local plant genera hosted 70 to 75 percent of the local moth and butterfly species. Those overachieving plants are the keystones.

“Keystone plants are unique components of local food webs that are essential to the participation of most other taxa in those food webs. Without keystone plants, the food web all but falls apart. And without some minimal number of keystone genera in a landscape, the diversity and abundance of many insectivores – the birds and bats, for example, that depend on caterpillars and moths for food – are predicted to suffer.” – Doug Tallamy, Nature’s Best Hope

The upshot? For our own landscapes to be as productive as possible, we need to include keystone plants. But how, you might ask, do I know what’s a keystone in my area? The National Wildlife Federation Native Plant Finder has your answer. For me, the medalists in the tree category are oaks, cherries and willows. In the flowers and grasses category, it’s goldenrods, sunflowers and grasses from the Panicum genus. These are the wolves to my backyard Yellowstone.  I’m nursing a tiny oak, a coupla fun-size black cherries, and a blanket of goldenrods in my yard right now. Going forward, I’ll want to work in some willows, sunflowers and switchgrasses.

Native sunflowers, probably Helianthus divaricata or helianthoides, in Wayne, PA. Photo by Lolly Jewett.

A native goldenrod, possibly Solidago odora, entertaining a plethora of pollinators in Dagsboro, DE. Photo by Lolly Jewett.

Meanwhile, over in London, the experience was a little different when they introduced werewolves.

If you live in the DC vicinity and could use assistance with sustainable landscaping, visit Bees’ Knees Design.

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Resources

Melissa Denchak, “Keystone Species 101,” NRDC, September 9, 2029.

Douglas W. Tallamy, Nature’s Best Hope, Timber Press, Portland, OR, 2020.

“Wolves of Yellowstone,” National Geographic.