Kevin Schofield's writings, observations, and other pointless distractions
You would have to be living in a cave not to be aware that there are many species on our planet that are in grave danger of going extinct in the near future. As a volunteer at the Woodland Park Zoo here in Seattle, I am armed with information about the endangered animals that are represented there and what individuals can do to help save them.
On the other hand, here are the facts: there are millions of species on our planet, all of which face an evolutionary struggle to adapt and survive. And the vast majority of species that have ever lived on our planet — by some estimations, 99% — have already gone extinct, either one at a time or through the (thankfully rare) “mass extinction events.” Extinction is not the exception; it’s by far the norm. So why are we getting so worked up about it?
Well, the emotional answer certainly has validity: there are a number of endangered species, e.g. tigers, elephants and cheetahs, that are beautiful, unique creatures and part of our planet’s natural history and heritage and are thus worth saving. Our planet is a richer place for being able to sustain them. In addition, their decline is due in large part to our encroachment on their habitat, so perhaps we have a moral responsibility toward their survival.
There is also a scientific argument, related to the notion of biodiversity: the “variety of life” or range of different organisms living sharing an environment. Back when I was in school, we talked about “food chains” in which this plant was eaten by this tiny bug, which was eaten by this kind of bird, which was hunted by this cat, which was preyed upon by this wolf. Very neat. In the subsequent time, we have expanded our view out to “food webs” in which we recognize that most species will eat a variety of different food sources, depending upon what is available and easiest to obtain. So rather than a simple chain, we end up with a complicated tangle of predator-prey relationships.
The good news is that food webs are resilient to removal of one prey species; consumption patterns will shift, but if the web is “dense” enough (meaning there are enough alternative food sources) then nothing dramatic will happen. But if the web gets thinned too much, then suddenly there is intense competition for the remaining food sources and populations of other species will likely decline. This can propagate through the middle layers of the web, and if too much thinning happens then the entire ecosystem can come crashing down. Bad things can also propagate down from the top layers: if a top predator is artificially removed, as happened with gray wolves in much of North America, then the population of its prey species can expand unchecked and overconsume its own food supplies, sending ripples down through the food web.
That’s a somewhat long-winded way of saying that biodiversity is important because it keeps our food webs dense, which is an important buffer for ecosystems as a whole against small population changes. Populations of individual species are constantly fluctuating, and ecosystems need to be resilient to that.
So here’s the next problem: there are so many species that are threatened right now, because of natural events, climate change, and human impact on habitats, that we can’t possibly focus on saving all of them. And besides, we know that trying to save every species isn’t the right answer, because that isn’t what happens in nature 99% of the time. So how do we, as a society, choose which ones to save?
The scientific research and environmental conservation communities have devised three categories of species that they believe are worthy of extra attention. While the reasoning behind each is a bit nuanced, each has unfortunately become a bit of a buzzword and is often thrown around loosely. But it’s worth understanding each of them, because behind each is a principle of how we should think about conservation in a big, complex, deeply interconnected world.
The first category is known as a “keystone species.” Much as a keystone in an arch supports the whole structure (and without it the arch would fall apart), a keystone species makes a unique contribution that enriches the ecosystem in a significant manner, often disproportionate to the population of that species. In other words, the species plays some critical role, without which the whole ecosystem would likely collapse. One example of a keystone species is wild Pacific salmon, which are born upstream in freshwater rivers and streams, migrate out to the ocean for most of their lives, and then return to their birthplace to spawn, die and decompose. Salmon’s keystone role is to carry back crucial nutrients from the sea to upstream freshwater locations, and replenish the water and land with those food sources — both their eggs and their own bodies. Another good example of a keystone species that I mentioned earlier is the gray wolf, which preys on ungulates such as elk. In fact, the wolf’s keystone contribution is to keep the ungulate population under control. Here in Washington state, where wolves were hunted to extinction, the elk population exploded; those elk stripped and ate bark off a large number of trees, killing or weakening the trees at a premature age and substantially thinning critical forest habitat for a wide variety of other species. Wolves are now carefully being re-introduced here as part of a larger plan to preserve forest habitat ecosystems. Endangered keystone species are high-priority candidates for conservation measures because the impact of their loss would be felt widely throughout the whole ecosystem.
The second category is an “indicator species.” This is a species that is particularly sensitive to a trait or characteristic of its environment, so its health can be a measurement for the health of the ecosystem as a whole. Mulluscs and mussels, which in aquatic environments are constantly filtering water through their system, are well-known indicators for pollution levels in the environment because their “bioaccumulation” of chemicals or other pollutants can affect their health (and can be checked through tests on the indicator species).
Here in the Pacific Northwest, the most notable and controversial indicator species is the Northern Spotted Owl. This beautiful creature is a habitat and prey specialist. It prefers to live, hunt and nest in forests with medium to large trees, a multi-layered canopy with significant overall light coverage, and lots of coarse, woody debris where its chief prey (flying squirrels, voles and woodrats) live. The only forests that meet those criteria are “old growth forests” with trees that are at least 50 years old — and in many cases hundreds of years old. The active and economically profitable logging industry in this region is good at replanting, but old growth forest takes hundreds of years to develop, so even replanted land is not a suitable habitat for spotted owls. Further, the spotted owls prefer large habitat patches over collections of smaller fragments, so it’s not enough to keep small preserves in several places; large tracts of old-growth forest need to be maintained.
Old growth forest is a rich, complex environment that supports a diverse food web that relies upon the same characteristics that the spotted owl prefers, which makes the spotted owl an ideal indicator species: if the owl is in decline then its entire ecosystem is under severe stress. And this is certainly the case: spotted owl numbers have been declining for decades. In 1990 it was listed as threatened, and since then the US Fish and Wildlife Service has been trying to protect old growth forest habitat in this area. Unfortunately, this created a conflict with the local timber industry as it constrained their ability to harvest lucrative lumber from those forests. The controversy around the spotted owl is a textbook case of the conservation community poorly explaining why it was focusing on the spotted owl; they let the debate be defined as “owls vs. jobs” without clearly explaining the significance of the owl as an indicator species for a larger ecosystem.
As an aside, pacific salmon are also an indicator species, for many of the same reasons as aquatic molluscs and mussels.
Indicator species make good targets for conservation because they focus our attention on specific underlying causes of ecosystem stress, and how to address them.
The third category of species is called an “umbrella species.” These are species that serve as effective proxies for a larger set of species that share not only a range of habitat but similar requirements within that range. Thus, protecting the umbrella species extends protection to many other animals at the same time without the need for individual focus on each of them. Most umbrella species are wide-ranging, have biology that is well documented, are easily sampled and/or observed, and have a long lifespan. These characteristics make it more straightforward to build a conservation plan, since its environmental requirements are well understood.
A great example of an umbrella species is the Florida panther. To quote the Fish and Wildlife Service project leader on panther conservation:
The Florida panther serves as an umbrella species. Because the species requires such a large home range, many plants and animals benefit from its protection and the protection of its habitat. Panthers prowl the same woods as black bear, coyotes, bobcats, white-tailed deer, wild hogs and many smaller mammals. Many varieties of birds, reptiles, amphibians live side-by-side with panthers. Rare tropical plants flourish in the south Florida wilderness where panthers roam. The ground water that the environment and the local human population depend on is recharged in the large tracts of undeveloped land that is home to the 80-100 panthers. By protecting habitat for panthers, we protect our environmental heritage and health, and provide a wildlife legacy for our children and the generations to come.
In many regions, butterflies and grasses are used as umbrella species.
Conservation efforts focused on umbrella species are highly leveraged: save one carefully-chosen, well-understood representative species, and you likely save many more.
You can see how these three categories, keystone, indicator, and umbrella, help us to decide where to focus our limited resources in conservation activities in order to maximize the impact. It’s not a perfect system, and there are constant arguments about priorities, but it is a thoughtful one based upon evidence.