A more broadly utilitarian argument for concern about loss of biological diversity is that—as seen in Chapters 8, 9 and 13—we do not yet know enough about the structure and function of ecosystems to be able to predict how much disturbance and species loss they can undergo yet still deliver ecosystem services upon which we depend.
We have just seen how poor our knowledge is simply about how many species of animals, plants, and microbes are present on Earth today. Additionally, for most of those species which have been named and recorded—the majority of which are invertebrates—we know little or nothing about the roles they play in maintaining the ecosystems of which they are part. One estimate is that we have information about the behaviour and ecology of fewer than 5% of all identified animal species (Raven, 2004). So it is not surprising that we are not yet very good at predicting the effects upon local or regional ecosystems of the loss of species as a consequence of habitat disturbance, or overexploitation, or introduction of alien species, or combinations of such perturbations.
The United Nations-sponsored Millennium Ecosystem Assessment, which involved some 1360 scientists from 95 countries and whose first global assessment of the world's ecosystems was published in 2005, represents a truly major effort to get to grips with these uncertainties (Millennium Ecosystem Assessment, 2005). It provides a comprehensive appraisal of the condition of, and trends in, the world's ecosystems. Ecosystem services are the benefit provided to humans as a result of species' interactions within the system. Some of these services are local (e.g. provision of pollinators for crops), others regional (e.g. flood control or water purification), and yet others global (e.g. climate regulation). In its massive report the Millennium Ecosystem Assessment identifies 24 categories of such ecosystem services, broadly grouped under three headings: provisioning, regulating, and cultural.
Table 15.1 summarizes these 24 categories of service, along with indications of whether the service is being enhanced or degraded. For provisioning services, enhancement is defined to mean increased production of the service through changes in area over which the service is provided (e.g. spread of agriculture or increased production per unit area). The production is judged to be degraded if the current use exceeds sustainable levels. For regulating services, enhancement refers to a change in the service that leads to greater benefits for people (e.g. the service of disease regulation could be improved by eradication of a vector known to transmit a disease to people). Degradation of regulating services means a reduction in the benefits obtained from the service, either through a change in the service (e.g. mangrove loss reducing the storm protection benefits of an ecosystem) or through human pressures on the service exceeding its limits (e.g. excessive pollution exceeding the capability of ecosystems to maintain water quality). For cultural services, degradation refers to a change in the ecosystem features that decreases the cultural (recreational, aesthetic, spiritual, etc.) benefits provided by the ecosystem.
Note that of the 24 categories of ecosystem services examined by the Millennium Ecosystem Assessment, 15—roughly two-thirds—are being degraded or used unsustainably. Whilst 15 have thus suffered, only four have been enhanced in the
Table 15.1 Global status of ecosystem services (Millennium Ecosystem Assessment, 2005).
Food crops livestock capture fisheries aquaculture wild foods Fibre timber cotton, hemp, silk wood fuel Genetic resources Biochemicals, natural medicines, pharmaceuticals Fresh water
Air-quality regulation Climate regulation global regional and local Water regulation Erosion regulation Water purification and waste treatment Disease regulation Pest regulation Pollination
Natural hazard regulation Cultural services
Spiritual and religious values Aesthetic values Recreation and ecotourism
Substantial production increase Substantial production increase Declining production due to overharvest Substantial production increase Declining production
Forest loss in some regions, growth in others Declining production of some fibres, growth in others Declining production
Lost through extinction and crop genetic resource loss Lost through extinction, overharvest
Unsustainable use for drinking, industry, and irrigation; amount of hydro energy unchanged, but dams increase ability to use that energy
Decline in ability of atmosphere to cleanse itself
Net source of carbon sequestration since mid-19th century
Preponderance of negative impacts
Varies depending on ecosystem change and location
Increased soil degradation
Varies depending on ecosystem change Natural control degraded through pesticide use Apparent global decline in abundance of pollinators Loss of natural buffers (wetlands, mangroves)
Rapid decline in sacred groves and species Decline in quantity and quality of natural lands More areas accessible but many degraded
+, enhanced; certainty'.
-, degraded, in the senses defined in the main text. *The evaluation here is of 'low to medium certainty'; all other trends are 'medium to high
past 50 years, of which three involve food production: crops, livestock, and aquaculture. The status of the remaining five is equivocal, as indicated in the table's notes.
The way economists conventionally calculate gross domestic product (GDP) takes little or no account of the role of ecosystem services. Thus an oil tanker going aground, and wreaking havoc on the region's biota, will typically make a positive contribution to conventional GDP (cleanup costs are a plus; environmental damage deemed not assessable). Costanza et al. (2001) have attempted to assess the 'GDP-equivalent' of the totality of the planet's ecosystem services. Their guesstimate is that such services have a value roughly equal to global GDP as conventionally assessed. Any calculation of this kind is beset with many uncertainties, and some would argue that you simply cannot put a price upon a service which is essential to life. But I find it helpfully indicative.
One important step in the direction of a more explicit and rigorous characterization of the components of ecosystem services is to develop indicators. It can be argued that ecologists and conservation biologists could learn from economists' long-standing set of common and clear indicators, used to track and influence the development of markets. Some recent work of this kind uses composite indicators from time-series data on populations of birds or other vertebrates (see Balmford et al., 2005). The UK uses one such indicator, the UK Wild Bird Index, to help evaluate the performance of its environmental policies (Gregory et al., 2004). There is clear need for further theoretical development of such measures of trends in biodiversity and general ecosystem health, carefully tested against relevant data (Crane 2003). And this practice is being extended within the European Union (Gregory et al., 2005).
As human numbers continue to grow, however, we need deeper understanding of how humans may alter habitats and ecosystems to provide for their needs, but do so subject to constraints which preserve both particular individual species and key elements of ecosystems. As discussed in Chapter 13, such 'co-use' will be no easy trick, involving detailed ecological understanding case by case. The alternative, however, would seem too often to be a mosaic of degraded habitat, increasingly threatening dedicated reserves, with all the tensions that entails. Terborgh's (1983) Five New World Primates is a pioneering work in this arena. It identifies a specific subset of tree species which would need to be kept in order for more intensive human exploitation of forests in the region of his study site to be reconciled with the continued survival there of five species of New World monkeys, all omnivores with a mixed diet of different fruits and small prey items. A more wide-ranging discussion of these issues, in an African context, is given by Western et al. (1994).
In essence, the broadly utilitarian argument recognizes that we do not know how much biological diversity we can lose, yet still keep ecosystem services on which humans depend. In this situation, as emphasized by one of the founders of the Conservation Movement, Aldo Leopold, 'the first rule of intelligent tinkering is to keep all the pieces'. But maybe we could be clever enough to survive in a greatly biologically impoverished world. It would, very likely, be a world akin to that of the cult movie Blade Runner. The question arises, who would want to live in such a world? This takes us to the third argument.
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