Decline and loss of species

Global biodiversity is changing at an unprecedented rate (Pimm and others 1995), the most important drivers of this change being land conversion, climate change, pollution, unsustainable harvesting of natural resources and the introduction of exotic species (Sala and others 2000). The relative importance of these drivers differs between ecosystems. For example, land conversion is most intensive in tropical forests and less intensive in temperate, boreal and Arctic regions; atmospheric nitrogen deposition is largest in northern temperate areas close to cities; introduction of exotic species is related to patterns of human activity - those areas remote from human intervention generally receive fewer introduced species. The ultimate causes of biodiversity loss are human population growth together with unsustainable patterns of consumption, increasing production of waste and pollutants, urban development, international conflict, and continuing inequities in the distribution of wealth and resources.

Over the past three decades, decline and extinction of species have emerged as major environmental issues. The current rate of extinction is many times higher than the 'background' rate - that which has prevailed over long periods of geological time. Estimates based on the fossil record suggest that the background extinction rate in mammals and birds has been one species lost every 500-1 000 years (May, Lawton and Stork 1995).

Information on the conservation status of species is provided by the World Conservation Union (IUCN) which regularly publishes 'Red Lists' of species considered to be threatened with extinction. The latest IUCN Red List (Hilton-Taylor 2000) indicates that about 24 per cent (1 130) of mammals and 12 per cent (1 183) of bird species are currently regarded as globally threatened (see table). Since the Red List assessment in 1996, the number of critically endangered species has increased from 169 to 180 mammals and from 168 to 182 birds (Hilton-Taylor 2000). Analyses suggest that over the next 100 years the extinction rate of vertebrate groups could be as high as 15-20 per cent (Mace 1995). However, species trends derived from Red List data should be interpreted with caution because the criteria for listing have changed over time and some of the changes in status reflect taxonomic revisions (May, Lawton and Stork 1995).

Insufficient information is available to determine precisely how many species have become extinct in the past three decades. However, the database maintained by the Committee on Recently Extinct Organisms (CREO 2001) lists 58 fish species and 1 mammal species recorded as extinct since 1970; assessments by BirdLife International indicate that 9 bird species have become extinct during this period (BirdLife International 2000).

Much of the relevant information on the status of species is qualitative or anecdotal, and it is therefore difficult to develop a quantitative overview of global trends. To assess trends in species loss or decline, indicators are required that provide quantitative estimates of change over time, using consistent methodologies for sampling and analysis. Ideally, such indicators should be based on data sampled explicitly for this purpose. Few such monitoring programmes have yet been established.

The Living Planet Index: a global biodiversity indicator
The Living Planet Index system is based on estimates of population size of individual wild species available in the scientific literature. The index is calculated as a percentage of the population size estimated at 1970; the mean value of the index is calculated as an average of all the species included in the assessment at each time interval (Groombridge and Jenkins 2000, Loh 2000, UNEP-WCMC 2000). The index has been calculated for the forest, marine and freshwater ecosystems (see graphs).

The forest index, based on 319 populations of temperate and tropical species (mostly birds), shows a decline of about 12 per cent during 1970-99. The index for temperate species only shows little change over the period (most deforestation here having taken place before the 20th century). The tropical sample shows a downward trend, consistent with the continuing deforestation in many tropical areas.

The marine index, based on populations of 217 species of marine animals, shows a decline of about 35 per cent in the same period.

Inland water and wetland species, represented by a sample of 194 populations, have declined by 50 per cent. This suggests that inland water ecosystems are more severely degraded than other ecosystem types, a finding consistent with other evidence.

Source: Loh 2000

One approach is the Living Planet Index created by UNEP-WCMC in cooperation with WWF (see box). The index is derived from trends in the size of wild populations of species in three habitats - forest, freshwater and marine ecosystems. The prevailing trend of all three indices is downward.

Globally threatened vertebrate species by region
  Mammals Birds Reptiles Amphibians Fishes Total
Africa 294 217 47 17 148 723
Asia and the Pacific 526 523 106 67 247 1 469
Europe 82 54 31 10 83 260
Latin America and Caribbean 275 361 77 28 132 873
North America 51 50 27 24 117 269
West Asia 0 24 30 8 9 71
Polar 0 6 7 0 1 14

Note: 'Threatened species' include those categorized by IUCN in 2000 as Critically Endangered, Endangered and Vulnerable (Hilton-Taylor 2000); adding totals for each region does not give a global total because a species may be threatened in more than one region.

Source: compiled from the IUCN Red List database (Hilton-Taylor 2000) and the UNEP-WCMC species database (UNEP-WCMC 2001a)

The impact of decline or loss of species on the provision of environmental services is difficult to evaluate because the relationship between species diversity and ecosystem function is still unclear. Some species are known to play more significant roles than others; these have been termed 'keystone' species - loss of one of these species has a particularly disruptive effect (Vitousek and Hooper 1993). Reductions in the number of species affect the provision of all ecosystem services because resource capture (of energy, water and nutrients) is greater in more diverse systems. Some ecosystems, such as arid and arctic areas, appear to be particularly vulnerable to human impacts. In these systems, relatively few organisms share common ecological roles (UNEP 1995). Species diversity may also play a role in buffering ecosystems against the effects of human activity (UNEP 1995).

The past three decades have been marked by the emergence of a concerted response to the biodiversity crisis. Civil society, particularly in the form of a hugely diverse and increasingly sophisticated NGO network, has been a major driving force behind this. A trend towards increased stakeholder participation relating to conservation action is evident as illustrated by the emergence of partnerships between NGOs, governments and the private sector.

A number of international conventions have been developed that deal specifically with conservation ofthreatened species. Among the most notable are the 1973 Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and the 1979 Convention on the Conservation of Migratory Species of Wild Animals (CMS) - or the Bonn Convention - which was developed to conserve terrestrial, marine and migratory bird species throughout their range. Inter-governmental agreements such as the African-Eurasian Waterbird Agreement - which aims to develop transboundary strategic measures necessary to conserve the network of critical wetland areas on which migratory waterbirds depend - are the primary tools for the implementation of the CMS.