The Shortfalls of Biodiversity
Meaningfully assessing the health and value of ecosystems requires far more than simply counting up all the species that live there.
Opinion by Peter Kareiva and Michelle Marvier
In 2011, shortly after one of us—Peter Kareiva—was promoted to Chief Scientist for The Nature Conservancy, TNC’s magazine published a much-discussed profile piece about Peter. The cause of all the controversy was a single quote in the opening paragraph, in which Peter stated that he was “not a biodiversity guy.” What could the Chief Scientist of the world’s largest conservation organization mean by such a surprising claim?
The word “biodiversity,” shorthand for biological diversity, entered the scientific literature in full force in 1988 when it appeared as the title of a National Academies report on the global extinction crisis. The term was coined to describe the diversity of life at all levels, from genes to ecosystems. It quickly took off and became a catchword on which to hang a growing concern about the extinction of species, the clearing of tropical rainforests, and the construction of roads, oil derricks, and shopping malls in what once were treasured landscapes.
Increasingly, scientists and science communicators are using the term biodiversity to represent everything that people love and value in nature. However, in practice, assessing biodiversity typically reduces to conducting a count of species. Similarly, focusing on biodiversity in conservation efforts often simply means attempting to secure as long a list of species as possible. And that, in turn, leads to some awkward priorities and practices.
If conservation is truly all about protecting the greatest diversity of species, then shouldn’t the Arctic and tundra ecosystems of the world fall pretty far down on our list of places to protect? And where is there room for iconic and grand landscapes such as Zion and Arches National Parks, which do not pass muster as biodiversity hotspots? We have argued elsewhere that landscapes with relatively low biodiversity (what we termed “biodiversity coldspots”) do, in fact, deserve protection for a wide variety of reasons, including the inspiration and other benefits these areas provide to people.
Non-native species, moved by people beyond their natural range, also create a conundrum. If conservation is all about biodiversity, and people want as many species as possible in our neighborhoods, then how should we think about non-native species? Dov Sax and colleagues were among the first to recognize that species introductions are increasing biodiversity, especially on islands. For example, due to invasions by non-native species, the total number of vascular plant species on the Hawaiian Islands has increased by 78%. Clearly, just tallying up the number of species is overly simplistic.
One reason conservationists are so concerned about biodiversity is that reductions in the number of species on local scales are thought to cause a loss of ecosystem services: less local biodiversity, fewer benefits to people. So, throughout the world, are we seeing a loss in local biodiversity? Astonishingly, the data say otherwise. For example, Mark Vellend and colleagues find that, because of non-native species, local biodiversity is on average staying the same or even increasing.
There are yet more pitfalls with focusing so much on the number of species in ecosystems. Ecology and evolutionary biology tell us that all species are not equal. Depending on which dimensions are considered most important, some species might be ten times as valuable as others. More specifically, ecologists have found that keystone species can play a disproportionate role in ecosystem dynamics, and their loss could lead to the extinction of dozens of other non-keystone species.
Meanwhile, evolutionary biologists have developed molecular tools that reveal the uniqueness of species in terms of their evolutionary lineage and divergence from their closest relatives. Imagine, for example, that you could protect only one of two endangered rodent species: either the Sri Lankan mountain rat (Rattus montanus) or Japan’s Ryukyu spiny rat (Tokudaia osimensis). The Sri Lankan mountain rat is a member of the genus Rattus comprising some 66 species, many of which are very abundant. In contrast, the Ryukyu spiny rat belongs to a genus consisting of only three living species, all of which are endangered or critically endangered. Thus you might choose to prioritize protection of the Ryukyu spiny rat, because if it went extinct a greater amount of evolutionary diversity would be lost with it. These are not disingenuous comparisons raised to make a point—counts of species, regardless of ecological and evolutionary distinctiveness, have been used to direct massive investments—as much as $750,000,000 for biodiversity hotspots as of 2003. We are not suggesting those monies were misspent, but rather that conservation needs to attend to a richer set of values than simply the count of species in a particular area.
And then there is the desire to engage the public. Conservation clearly needs broad public support, but have you ever tried to inspire the public with the phrase “biodiversity”? One barrier is that many people have no idea what you’re talking about. A 2013 poll found that about half of European Union residents either have never heard the term biodiversity (26%) or have heard it but don’t know what it means (30%). This is consistent with polls conducted in the UK in 2011 that found 32% of residents had never heard the word and an additional 18% said they had heard it but knew nothing more about it. Based on polls conducted in the U.S., conservationists have been advised to avoid using the word biodiversity in messages aimed at increasing public support for conservation. The words that conservationists choose really matter: A 2004 poll conducted by the Yale Center for Environmental Law and Policy found that only 50% of Americans felt that “loss of biodiversity” was a serious concern, compared to 78% who reported high concern over “extinction of wildlife species.”
Finally, there is the issue of whether biodiversity can be quantified in any practical way that would allow conservationists to track how effective their efforts have been. In the first Convention on Biodiversity, introduced at the 1992 Rio Earth Summit, a focal objective was to slow the rate of biodiversity loss. Given that the total number of Earth’s species is not known and estimates of extinction vary widely, no monitoring program or set of indicators has been designed that can possibly detect a deceleration in the rate of species loss. In fact, when the Biodiversity Working Group examined the issue of indicators for the Rio Convention it highlighted the “lack of clarity about what is meant by biodiversity and therefore on how best to measure it.”
When we say we are not biodiversity guys or gals, does that mean we are against biodiversity? No. It means we prefer to frame conservation’s objectives around richer and more nuanced concepts than the length of a species list. We do not think the concept of biodiversity does justice to the wonders and beauty of the nature that we hope to protect.
There is simply too much overlooked or neglected by an obsession with counting species. By reducing our assessment of nature to a simple tally, we fail to realize some of the amazing things going on in our world. For example, there are now some 4,000 coyotes in Chicago, and a new species of subway-dwelling, human-biting mosquito recently evolved from an above-ground bird-biting species. And at the frontier of conservation science, biologists are debating whether they should use cloning techniques to bring extinct species back to life.
Humans don’t just destroy species—we also create new forms and combinations of life. Joseph Bull and Martine Maron recently documented that the creative impact of humans in terms of generating new forms of life is on par with the destructive force of humans in terms of extirpating species. Yes, there have been 1,359 documented extinctions since the end of the last ice age. But there have also been more than 743 species domesticated and another 891 species moved around the world. Thus, it is fair to say humans have accounted for what can be viewed as at least 1,634 new forms of biodiversity—a number on par with the 1,359 lost forms. We would never claim these human creations can possibly replace what has been lost. But again the point is that simple tallies of species miss too much of what is going on.
Conservation is an act of love and passion. Ecologists become ecologists because they love the details of natural history and the surprises of species interactions. In an eloquent ode to natural history, Jennifer Frazer remarks on how biology is now taught at such an abstract conceptual level that the wonders of natural history, the exact wonders that inspire people to care about nature, are diminished. While we fully understand the scientific appeal of focusing on biodiversity, we feel this framework is an abstraction and form of numerology that underperforms as a motivator for conservation. The term biodiversity adds a veneer of science over the messy, complicated, often emotional concept of nature. In so doing, it has the inverse effect of what a veneer is meant to do. In furniture making, a veneer covers homogeneous, unattractive particle board to add the beauty and complexity of natural wood. However, applying the scientific veneer of biodiversity to nature has the opposite effect: the underlying material—life in all its natural beauty and complexity—is diminished by the addition of a thin layer of objective, dispassionate science.
The term biodiversity was created to capture something that is rich and complicated and culturally dependent. However, the reality is that by focusing on biodiversity, we often reduce the amazing variety of life to a single number, and in that process we lose too much. Nature is not a stamp collection—it’s a vibrant, dynamic web of interacting species.
We stand by the quote. Neither of us is a “biodiversity guy”—we always have been, and remain, ecologists.
Illustrations by Scott Menchin