(Nov. 28th, 2009) In this second article, Jeremy Garwood looks at who determines which living species most need saving and where they are most in danger of extinction.
A growing awareness that biological extinction rates are rapidly rising as a consequence of human economics has lead to demands to do something to slow or even reverse the tendency. However, this has revealed two problems that have demanded a lot of research in themselves. Firstly, which species are the most at risk of extinction and where do they live? Second, what can scientists do to prevent extinction and, with limited funding, which strategies are optimal?
The “Red List” from the IUCN (International Union for Conservation of Nature) is the most well-established databank for identifying species in danger of extinction. Started in the 1950’s, these lists of threatened species are regularly updated and serve as a focus for conservation priorities. But how reliable is the information given?
As Edward Wilson, from Harvard’s Museum of Comparative Zoology, explains: “Few biologists other than systematists appreciate how little is known of Earth’s biodiversity. Estimates of the total numbers of species still vacillate wildly.” Between 3.6 and 111.7 million species! (‘On the future of conservation biology’, Conservation Biology, 2000). But, “the estimated number of species actually described and given scientific names ranges between 1.5 and 8 million. Even figures for the relatively well-studied vertebrates are spongy.” And their Natural History is still further behind: “Even among named species, only a minute fraction, less than 1%, have been studied beyond the essentials of habitat preference and diagnostic anatomy.” In general, Wilson concludes, “ecologists and conservation biologists appear not to fully appreciate how thin the ice is on which they skate.”
In this context, the quantitative evaluations used by IUCN to compile their Red Lists are easy to criticise. In particular, the lack of a global overview - some species only live in one or two locations, others are more widespread – is the threat to their survival the same at each location? And what about all the unknown species?
Global Template Mapping
What alternative criteria exist when establishing priorities for global biodiversity conservation? In 2006, Science published a comparative review of nine major institutional “templates” (Brooks et al. ‘Global biodiversity conservation priorities’). These global maps identified ‘Crisis Ecoregions’, ‘Biodiversity Hotspots’ (defined as “34 biogeographically similar aggregations of ecoregions holding 0.5% of the world’s plants as endemics, and with 70% of primary habitat already lost”), ‘Endemic Bird areas’, ‘Centers of Plant Diversity’ (another IUCN study identifying “234 mainland sites holding >1,000 plant species, of which 10% are endemic either to the site or the region; or islands containing 50 endemic species or 10% of flora endemic”), ‘Megadiversity Countries’, ‘Global 200 ecoregions’ (from the US World Wildlife Fund), ‘High-biodiversity wilderness areas’ (= “5 biogeographically similar aggregations of ecoregions with 0.5% of the world’s plants as endemics, and with 70% of primary habitat remaining and 5 people per km2”), ‘Frontier Forests’, and the evocatively titled, ‘Last of the Wild’ (featuring the “10% wildest 1-km2 grid cells in each biome, and wildness measured from an aggregate index of human density, land transformation, access, and infrastructure”). All of these “templates” fit within the framework of “irreplaceability” of species relative to their “vulnerability”. This is “central to conservation planning theory”, yet the maps end up highlighting different regions. Why?
Although most of them prioritized “high irreplaceability”, some chose “high vulnerability” and others were more interested in “low vulnerability”. It appears that “irreplaceability”, chosen by 6 out of the 9 is based on subjective measures derived from the opinions of specialists. Meanwhile the 5 templates that stressed vulnerability used four different measures of vulnerability: (i) environmental and spatial variables, (ii) land tenure, (iii) threatened species, and (iv) expert opinion.
Brooks concluded that: “Global conservation planning is key for strategic allocation of flexible resources,” and that “despite divergence in methods between the different schemes, an overall picture is emerging in which a few regions, particularly in the tropics and in Mediterranean-type environments, are consistently emphasized as priorities for biodiversity conservation. It is crucial that the global donor community channel sufficient resources to these regions, at the very minimum.”
Genetic and evolutionary value – not all species are equal!
Some biologists argue that species differ substantially in the amount of unique genetic information they embody. David Redding and Arne Mooers from Canada’s Simon Frazier University explain that “if species were ranked for conservation purposes based on these metrics, resources would be preferentially allocated to those species that embody disproportionately large amounts of unique genetic information above those with many close relatives” (‘Incorporating evolutionary measures into conservation prioritization’, Conservation Biology, 2006).
They have developed a prioritization for 9546 bird species that takes account of their places in the entire taxonomic tree of birds as a measure of “the evolutionary history that each species embodies”, then combined this genetic value with each species’ probability of extinction to create a “species-specific measure of expected loss of genetic information.” By this measure, the species with the highest value, embodying some 92.31 million years (MY) of evolutionary history, was Strutho camelius, the Southern Ostrich, due to its “basal and monotypic status”. Similarly, species like kiwis (there are 3 Apterygidae species) and the ‘Plains Wanderer’ (Pedionomus torquatus), leapt up the conservation lists when their genetic status was assessed at 28.34 MY and 53.6 MY, respectively. The mean value for the 9546 bird species was “just” 8.319 MY, but fully 73% of species had values below the mean. Redding and Mooers found that “threatened species embodied more evolutionary history than expected by chance”.
Incorporating such evolutionary measures could prevent the “inadvisability” of risking the loss of genetic information “by waiting until valuable species have become highly threatened.”
Localised Hotspot Choices
However it is assessed, the spatial distribution of genetic material across the Earth’s surface is far from uniform. As Myers et al. reported in Nature (‘Biodiversity hotspots for conservation priorities’, 2000), “44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth.”
Yet, it is one thing knowing where species and their ecosystems are in danger of extinction, it is another understanding the nature of that threat and how best to address it. There is currently a heated scientific debate between idealists who want to save everything and economic pragmatists who explain that, with limited funding for conservation projects, some hard decisions need to be made.
In the third part of this online series, Jeremy Garwood describes how endangered species are now being equated to human battlefield victims in an army field hospital. With limited resources and an endless stream of wounded and dying, it is argued that we should only actively save those that can be saved, passively allowing the rest to die of their wounds.