Box 1.3. Ecological Indicators and Biodiversity

The National Research Council in the United States identified three categories of ecological indicators, none of which adequately assesses the many dimensions of biodiversity:

• Ecosystem extent and status (such as land cover and land use) indicates the coverage of ecosystems and their ecological attributes.
• Ecological capital, further divided into biotic raw material (such as total species richness) and abiotic raw materials (such as soil nutrients), indicates the amount of resources available for providing services.
• Ecological functioning (such as lake trophic status) measures the performance of ecosystems.

Care must therefore be taken not to apply ecological indicators to uses they were not intended for, especially when assessing biodiversity. For example, biotic raw ecological capital measures the amount and variability of species within a defined area (C2.2.4). This may seem related to biodiversity, but it measures only taxonomic diversity. As such, this indicator does not necessarily capture many important aspects of biodiversity that are significant for the delivery of ecosystem services.

The most common ecological indicator, total species richness, is a case in point. TSR only partially captures ecosystem services. It does not differentiate among species in terms of sensitivity or resilience to change, nor does it distinguish between species that fulfill significant roles in the ecosystem (such as pollinators and decomposers) and those that play lesser roles. That is, all species are weighted equally, which can lead assigning equal values to areas that have quite different biota. Moreover, the value of TSR depends on the definition of the area over which it was measured and may scale neither to smaller nor to larger areas. Finally, TSR does not differentiate between native and non-native species, and the latter often include exotic, introduced, or invasive species that frequently disrupt key ecosystem services. Ecosystem degradation by human activities may temporarily increase species richness in the limited area of the impact due to an increase in exotic or weedy species, but this is not a relevant increase in biodiversity (C2.2.4).

Given the limitations of ecological indicators to serve as adequate indicators of biodiversity, work is urgently needed to develop a broader set of biodiversity indicators that are aligned against valued aspects of biodiversity. With the exception of diversity indices based on taxonomic or population measures, little attention has been paid to the development of indicators that capture all the dimensions of biodiversity (C4.5.1), although see Key Question 6 and C4.5.2 for more on indicators for the “2010 biodiversity target.”

Source: Millennium Ecosystem Assessment
  Ecosystems and Human Well-being: Biodiversity Synthesis (2005), p.21