Are some species more important than others?

Conservation efforts, by definition, are aimed at keeping things as they were. When this is impossible, ecologists and policy makers try to at least minimize anthropogenic damage to the Earth's species, without attempting so many simultaneous tasks that each effort becomes ineffectual. The species that receive this sort of triage tend to be taxonomically unique, such as the tuatara, or charismatic megavertebrates, such as the giant panda. Such a strategy prioritizes species over ecosystems, and can only be undertaken with the understanding that eventually all the tuataras and pandas on Earth may only be able to live in zoos. However, triage remains a potentially useful tool if it is applied based strictly on ecological importance. If conservationists focus on keystone species and ecosystem engineers, they will be most able to protect diversity and maintain structure within threatened ecosystems.

Keystone species are usually understood to act trophically and to exert an effect disproportionate to their relative biomass within an ecosystem. They often occur at or near the highest trophic levels of a food web, as carvinores with high per capita effects and low collective biomass. However, keystones can act non-trophically as well, pollinating or dispersing other species. The textbook case of a keystone species is the starfish Pisaster, which plays a major role in supporting diversity. In one computer simulation, when it is removed, the Simpson Diversity Score¹ of its ecosystem fell by 4 points, as the Pisaster’s prey were allowed to competitively exclude each other. Other species in the same simulation exerted far less of an effect on their biotic environments (Power 1996).

A species can also be of particular importance to the physical structure of an environment. Ecosystem engineers change the quality, quantity, and distribution of resources other than their own biomass. These organisms allogenically construct or autogenically compose entire habitats such as coral reefs, forests, and beaver ponds; in doing so they affect key environmental attributes such as nutrient mixing, temperature, and drainage. Excepting ecosystem engineers which are also keystone species, such as beavers, leaf-cutter ants, and badgers, ecosystem engineers commonly live at high densities and, like Antarctic algae or reef building coral, may be near the lowest trophic level of a food web (Lawton 1994). Their effects are drastic, but can be taken for granted, potentially causing them to be overlooked in conservation efforts.

There are, however, some ecosystem functions to which all species contribute equally. Low-diversity communities constructed experimentally so as to resemble depauperate descendants of high-diversity communities show decreased rates of carbon dioxide uptake and decreased plant productivity, with a constant decline in each function confirming Lawton’s “ratchet” hypothesis (1994). Another caveat lies in the fact that many studies that appear to attribute a major role to a given species in fact attribute that role to a given guild. A hypothetical experiment which labels an ecosystem’s decomposer as an ecosystem engineer does not determine whether ecosystem function is further dependent on a diverse guild of decomposers, or whether one species is sufficient. And even seemingly redundant species can contribute to an ecosystem’s resistance and resilience in the face of disturbances that may never be experimentally observed (Walker 1992). Conclusive decisions as to the allocation of conservation resources can only be made for ecosystems that are thoroughly studied and well understood, and even then minor-interactors must never be written off entirely.


Works Cited:

• Lawton, H. What do species do in ecosystems? OIKOS 71(3), 1994.
• Power, M.E. and others. Challenges in the Quest for Keystones. BioScience 46 (8): 609-620, 1996.
• Walker, B. H. Biodiversity and ecological redundancy. Conservation Biology 6 (1): 18-23, 1992.

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¹This is a unitless ranking of an ecosystem's diversity that takes both its richness (the number of different species it contains) and eveness (the degree to which species are spatially interspersed with each other) into account.

Methinks someone has been taking a class in conservation ecology. While everything Metacognizant says is true, there are some important omissions. The write-up represents an important position being debated in modern ecology, but I feel that one of the alternate positions must be presented.

First, Metacognizant is quite right in pointing out that much of the public focus on conservation often targets species or ecosystems of little global (or even local) importance. The focus on taxonomic oddities or 'fuzzy and cute' animals is the norm in the public sphere, causing many scientists and more fervent conservationists fits. For example, the great white shark is currently under significant pressure, and is very close to being listed as an endangered species. It is already recognized by most as a species at risk given its low reproductive rate and very slow growth. However, the public face of the great white is Jaws, not a key player in the ocean ecosystem. As such, it is nigh impossible to have a fund-raiser to help protect the shark.

It is important, though, to know that in academic or government institutions this is not the trend. Saving the whales, pandas and dolphins is normally the thrust of charitable and fund-raising efforts (think of the World Wildlife Fund or Greenpeace), while the real work of natural resource managers and researchers is considerably less glamourous. For example, the majority of the work conducted by government regulators deals with issues such as shoreline conservation, septic tanks and beds, hunting regulations, agricultural run-off and invasive species. While it may seem as though too much money is going to save the Tuatara given its relative lack of importance to the functioning of the New Zealand biome, that is only true when examined as a fraction of the money donated to conservation efforts by private citizens. In reality, far more money is spent re-landscaping river plains and treating waste-water for phosphorus and bacteria. Your tax dollars are spent dealing with the non-glamourous and non-sexy issues that won't catch the public's eye, but nonetheless need to be done lest we all find ourselves living in a cesspool.

Metacognizant also argues that the limited resources we have to devote to conservation should be spent in such a manner as to maintain ecosystem function, rather than character. This is beyond dispute in both the scientific community. Having 1000 pandas living in a fenced-in bamboo monoculture is of no use to anyone; it is not sustainable, and does nothing to create a future hope for these animals. However, the concerns of many conservationists go beyond questions of function alone. Is the Tuatara is no more important than any other large insectivorous reptile? Is it no more than the niche which it fills? By conserving only the function of an ecosystem undervalues the historical significance of many creatures. Ethically, many conservationists argue not just for the maintenance of function, but also for the maintenance of form. There is a strong and defensible belief that we do not have the right to exterminate a species which has managed to survive millions of years in the face of innumerable perils.

Beyond pure ethics, there is a practical reason to continue to conserve the weird and cute. For some people, the stars represent untold mysteries and wonder; looking into the night sky, knowing that light travelled unimaginable distances to grace your eyes with its glimmer is a humbling and magical experience. For others, this same sense of wonder can be had when looking to such a beast as the Tuatara or the Coelocanth; how precious the chance to live in a world where such an animal, out of time, can honour you with its presence. These people would argue that these animals must be protected for the sake of ethics and also in order to capture the imaginations of others around the world.

As a personal aside, I find that in modern academic ecology and conservation biology, there is a tendancy to lose the fight before it can be engaged. That is, many of us tend to look at the world as would an accountant or a CEO. Given limited resources with which to conserve, let us conserve only the essentials, and things like wonder and beauty simply don't enter in to the equation. The debate shouldn't be whether we attempt to preserve the function of the ecosystems in the most efficient way possible; it should be about how much wonder (and function) we're willing to sacrifice as we continue to expand and use the earth's resources.