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Box 1.2. Measuring and Estimating Biodiversity: More than Species Richness

Measurements of biodiversity seldom capture all its dimensions, and the most common measure—species richness—is no exception. While this can serve as a valuable surrogate measure for other dimensions that are difficult to quantify, there are several limitations associated with an emphasis on species. First, what constitutes a species is not often well defined. Second, although native species richness and ecosystem functioning correlate well, there is considerable variability surrounding this relationship. Third, species may be taxonomically similar (in the same genus) but ecologically quite distinct. Fourth, species vary extraordinarily in abundance; for most biological communities, only a few are dominant, while many are rare.

Simply counting the number of species in an ecosystem does not take into consideration how variable each species might be or its contribution to ecosystem properties. For every species, several properties other than its taxonomy are more valuable for assessment and monitoring. These properties include measures of genetic and ecological variability, distribution and its role in ecosystem processes, dynamics, trophic position, and functional traits.

In practice, however, variability, dynamics, trophic position, and functional attributes of many species are poorly known. Thus it is both necessary and useful to use surrogate, proxy, or indicator measures based on the taxonomy or genetic information. Important attributes missed by species or taxon-based measures of diversity include:

  • abundance—how much there is of any one type. For many provisioning services (such as food, fresh water, fiber), abundance matters more than the presence of a range of genetic varieties, species, or ecosystem types.
  • variation—the number of different types over space and time. For understanding population persistence, the number of different varieties or races in a species or variation in genetic composition among individuals in a population provide more insight than species richness.
  • distribution—where quantity or variation in biodiversity occurs. For many purposes, distribution and quantity are closely related and are therefore generally treated together under the heading of quantity. However, quantity may not always be sufficient for services: the location, and in particular its availability to the people that need it, will frequently be more critical than the absolute volume or biomass of a component of biodiversity.Finally, the importance of variability and quantity varies, depending on the level of biodiversity measured. (See Table.)
LevelImportance of Variability Importance of Quantity and Distribution
Genes adaptive variability for production and resilience to environmental change, pathogens, and so on local resistance and resilience
Populationsdifferent populations retain local adaptation local provisioning and regulating services, food, fresh water
Speciesthe ultimate reservoir of adaptive variability, representing option values community and ecosystem interactions are enabled through the co-occurrence of species
Ecosystemsdifferent ecosystems deliver a diversity of rolesthe quantity and quality of service delivery depend on distribution and location

Source: Millennium Ecosystem Assessment
  Ecosystems and Human Well-being: Biodiversity Synthesis (2005), p.20

Related publication:
Biodiversity (MA) homeBiodiversity & Human Well-being
Other Figures & Tables on this publication:

Direct cross-links to the Global Assessment Reports of the Millennium Assessment

Box 1. Biodiversity and Its Loss— Avoiding Conceptual Pitfalls

Box 1.1. Linkages among Biodiversity, Ecosystem Services, and Human Well-being

Box 1.2. Measuring and Estimating Biodiversity: More than Species Richness

Box 1.3. Ecological Indicators and Biodiversity

Box 1.4. Criteria for Effective Ecological Indicators

Box 2. MA Scenarios

Box 2.1. Social Consequences of Biodiversity Degradation (SG-SAfMA)

Box 2.2. Economic Costs and Benefits of Ecosystem Conversion

Box 2.3. Concepts and Measures of Poverty

Box 2.4. Conflicts Between the Mining Sector and Local Communities in Chile

Box 3.1. Direct Drivers: Example from Southern African Sub-global Assessment

Box 4.1. An Outline of the Four MA Scenarios

Box 5.1. Key Factors of Successful Responses to Biodiversity Loss

Figure 3.3. Species Extinction Rates

Figure 1.1. Estimates of Proportions and Numbers of Named Species in Groups of Eukaryote Species and Estimates of Proportions of the Total Number of Species in Groups of Eukaryotes

Figure 1.2. Comparisons for the 14 Terrestrial Biomes of the World in Terms of Species Richness, Family Richness, and Endemic Species

Figure 1.3. The 8 Biogeographical Realms and 14 Biomes Used in the MA

Figure 1.4. Biodiversity, Ecosystem Functioning, and Ecosystem Services

Figure 2. How Much Biodiversity Will Remain a Century from Now under Different Value Frameworks?

Figure 2.1. Efficiency Frontier Analysis of Species Persistence and Economic Returns

Figure 3. Main Direct Drivers

Figure 3.1. Percentage Change 1950–90 in Land Area of Biogeographic Realms Remaining in Natural Condition or under Cultivation and Pasture

Figure 3.2. Relationship between Native Habitat Loss by 1950 and Additional Losses between 1950 and 1990

Figure 3.3. Species Extinction Rates

Figure 3.4. Red List Indices for Birds, 1988–2004, in Different Biogeographic Realms

Figure 3.5. Density Distribution Map of Globally Threatened Bird Species Mapped at a Resolution of Quarter-degree Grid Cell

Figure 3.6. Threatened Vertebrates in the 14 Biomes, Ranked by the Amount of Their Habitat Converted by 1950

Figure 3.7. The Living Planet Index, 1970–2000

Figure 3.8. Illustration of Feedbacks and Interaction between Drivers in Portugal Sub-global Assessment

Figure 3.9. Summary of Interactions among Drivers Associated with the Overexploitation of Natural Resources

Figure 3.10. Main Direct Drivers

Figure 3.11. Effect of Increasing Land Use Intensity on the Fraction of Inferred Population 300 Years Ago of Different Taxa that Remain

Figure 3.12. Extent of Cultivated Systems, 2000

Figure 3.13. Decline in Trophic Level of Fisheries Catch since 1950

Figure 3.14. Estimated Global Marine Fish Catch, 1950–2001

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.16. Fragmentation and Flow in Major Rivers

Figure 3.17 Trends in Global Use of Nitrogen Fertilizer, 1961–2001 (million tons)

Figure 3.18 Trends in Global Use of Phosphate Fertilizer, 1961–2001 (million tons)

Figure 3.19. Estimated Total Reactive Nitrogen Deposition from the Atmosphere (Wet and Dry) in 1860, Early 1990s, and Projected for 2050

Figure 3.20. Historical and Projected Variations in Earth’s Surface Temperature

Figure 4. Trade-offs between Biodiversity and Human Well-being under the Four MA Scenarios

Figure 4.1. Losses of Habitat as a Result of Land Use Change between 1970 and 2050 and Reduction in the Equilibrium Number of Vascular Plant Species under the MA Scenarios

Figure 4.2. Relative Loss of Biodiversity of Vascular Plants between 1970 and 2050 as a Result of Land Use Change for Different Biomes and Realms in the Order from Strength Scenario

Figure 4.3. Land-cover Map for the Year 2000

Figure 4.4. Conversion of Terrestrial Biomes

Figure 4.5. Forest and Cropland/Pasture in Industrial and Developing Regions under the MA Scenarios

Figure 4.6. Changes in Annual Water Availability in Global Orchestration Scenario by 2100

Figure 4.7. Changes in Human Well-being and Socioecological Indicators by 2050 under the MA Scenarios

Figure 6.1. How Much Biodiversity Will Remain a Century from Now under Different Value Frameworks?

Figure 6.2. Trade-offs between Biodiversity and Human Well-being under the Four MA Scenarios

Table 1.1. Ecological Surprises Caused by Complex Interactions

Table 2.1. Percentage of Households Dependent on Indigenous Plant-based Coping Mechanisms at Kenyan and Tanzanian Site

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Provisioning services

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Regulating services

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Cultural services

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Supporting services

Table 6.1. Prospects for Attaining the 2010 Sub-targets Agreed to under the Convention on Biological Diversity