How to Save an Evolutionarily Significant Unit

Geneticists don’t like species. And to be fair, there are as many definitions of a ‘species’ as there are scientists. What’s a ‘species’ when bacteria are concerned? The term is meaningless. Even a lot of plants and fungi defy our traditional concepts. The closer we study nature, the more cracks begin to appear. But don’t worry, that’s exactly how science is supposed to work. Our understanding gradually improves with each discovery, and our description of the natural world is refined. Nobody said science was speedy. We are far more concerned with accuracy. And the geneticists tell us that if we want to be accurate, we need to stop talking about species.

Many of the foundational pillars of conservation were devised by geneticists. Many of our management methods arose with genetic viability in mind. Captive rearing and species reintroduction efforts take care to avoid inbreeding and outbreeding depressions. The 50/500 rule, infamous in the field of conservation, in part seeks to combat the loss of genetic material through drift. And nowadays, if you read modern recovery plans for threatened and endangered species, you’ll struggle to find the word ‘species’. Curious. The language has shifted in the last few decades; we now concern ourselves with ‘evolutionarily significant units’. You can see why it hasn’t caught on in day to day parlance. Not very pithy, I’ll admit, but again we are going for accuracy, and conservation biology in particular, is above all else concerned with success.

The geneticists tell us that if we ignore ESUs, we risk constant and repeated failure. Moreover, we may not even realize we have failed until it is too late. Indeed one of the greatest challenges in conservation is measuring your impact, i.e. quantifying success. California condors have increased from around 20 individuals in the 1970’s to 300 individuals at the time of writing. Sounds pretty successful. But if these birds disappear in a century’s time, have we achieved anything? Even the entirety of human history is a blink of an eye in evolutionary terms, so to see conservation goals only extending over decades, as opposed to millennia, is somewhat troubling. The geneticists are much better at long-term thinking. Not only do they think in timescales more in line with natural processes, but they also seek to preserve the raw materials that allow organisms to persist in perpetuity. Surely this must be the ultimate goal of conservation – self-sufficiency. We must see the return of biological communities that do not require human intervention; we must safeguard organisms that can adapt to future conditions, and survive environmental perturbations. If this is not achieved, can we really claim success?

Any species (sorry, ESU, old habits…) or ecosystem that cannot sustain itself without constant supervision is not long for this earth. It won’t be cheap to get nature back on its feet, but this must be weighed against the cost of indefinite management. I would argue the latter is ruinously expensive. Prohibitively expensive. The longer we argue over the economics of conservation, the worse the situation becomes. The price of our ambivalence grows with each passing day. We can no longer afford to be idle on this issue. I’m not sure we could ever afford it. Many animals and biological systems currently hang by a thread. Indeed some fear that the wanton destruction of the environment in recent years has made self-sufficiency a pipe dream. But in the immortal words of Richard Hofstadter, “in so far as the weight of one’s will is thrown onto the scales of history, one lives in the belief that this is not so.”

Over geological epochs, generations turnover like dominoes as successful genotypes march through time. This is the most accurate view of the world we have. For conservation to be successful we must plan on colossal timescales, because we are attempting to preserve colossal processes.  For now ESUs apply to populations within a species range that harbor unique genetic lineages or represent separate fishing stocks. In time we will apply the ESU concept to predator-prey guilds and ecosystems. Genetics reminds us to manage the natural world on a timescale that nature understands.

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