Ecosystems and Human Well-being: Biodiversity Synthesis: Key Questions on Biodiversity in the Millennium Ecosystem Assessment
Biodiversity: What is it, where is it, and why is it important?
- Biodiversity is the variability among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species, and of ecosystems.
- Biodiversity forms the foundation of the vast array of ecosystem services that critically contribute to human well-being.
- Biodiversity is important in human-managed as well as natural ecosystems.
- Decisions humans make that influence biodiversity affect the well-being of themselves and others.
What Is Biodiversity?
Biodiversity is the foundation of ecosystem services to which human well-being is intimately linked. No feature of Earth is more complex, dynamic, and varied than the layer of living organisms that occupy its surfaces and its seas, and no feature is experiencing more dramatic change at the hands of humans than this extraordinary, singularly unique feature of Earth. This layer of living organisms—the biosphere—through the collective metabolic activities of its innumerable plants, animals, and microbes physically and chemically unites the atmosphere, geosphere, and hydrosphere into one environmental system within which millions of species, including humans, have thrived. Breathable air, potable water, fertile soils, productive lands, bountiful seas, the equitable climate of Earth’s recent history, and other ecosystem services (see Box 1.1 and Key Question 2) are manifestations of the workings of life. It follows that large-scale human influences over this biota have tremendous impacts on human well-being. It also follows that the nature of these impacts, good or bad, is within the power of humans to influence (CF2).
Defining Biodiversity
Biodiversity is defined as “the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.” The importance of this definition is that it draws attention to the many dimensions of biodiversity. It explicitly recognizes that every biota can be characterized by its taxonomic, ecological, and genetic diversity and that the way these dimensions of diversity vary over space and time is a key feature of biodiversity. Thus only a multidimensional assessment of biodiversity can provide insights into the relationship between changes in biodiversity and changes in ecosystem functioning and ecosystem services (CF2).
Biodiversity includes all ecosystems—managed or unmanaged. Sometimes biodiversity is presumed to be a relevant feature of only unmanaged ecosystems, such as wildlands, nature preserves, or national parks. This is incorrect. Managed systems—be they plantations, farms, croplands, aquaculture sites, rangelands, or even urban parks and urban ecosystems—have their own biodiversity. Given that cultivated systems alone now account for more than 24% of Earth’s terrestrial surface, it is critical that any decision concerning biodiversity or ecosystem services address the maintenance of biodiversity in these largely anthropogenic systems (C26.1).
Measuring Biodiversity: Species Richness and Indicators
In spite of many tools and data sources, biodiversity remains difficult to quantify precisely. But precise answers are seldom needed to devise an effective understanding of where biodiversity is, how it is changing over space and time, the drivers responsible for such change, the consequences of such change for ecosystem services and human well-being, and the response options available. Ideally, to assess the conditions and trends of biodiversity either globally or sub-globally, it is necessary to measure the abundance of all organisms over space and time, using taxonomy (such as the number of species), functional traits (for example, the ecological type such as nitrogen-fixing plants like legumes versus non-nitrogen-fixing plants), and the interactions among species that affect their dynamics and function (predation, parasitism, competition, and facilitation such as pollination, for instance, and how strongly such interactions affect ecosystems). Even more important would be to estimate turnover of biodiversity, not just point estimates in space or time. Currently, it is not possible to do this with much accuracy because the data are lacking. Even for the taxonomic component of biodiversity, where information is the best, considerable uncertainty remains about the true extent and changes in taxonomic diversity (C4).
| Box 1.1. Linkages among Biodiversity, Ecosystem Services, and Human Well-being |
 Biodiversity represents the foundation of ecosystems that, through the services they provide, affect human well-being. These include provisioning services such as food, water, timber, and fiber; regulating services such as the regulation of climate, floods, disease, wastes, and water quality; cultural services such as recreation, aesthetic enjoyment, and spiritual fulfillment; and supporting services such as soil formation, photosynthesis, and nutrient cycling (CF2). The MA considers human well-being to consist of five main components: the basic material needs for a good life, health, good social relations, security, and freedom of choice and action. Human well-being is the result of many factors, many directly or indirectly linked to biodiversity and ecosystem services while others are independent of these. |
There are many measures of biodiversity; species richness (the number of species in a given area) represents a single but important metric that is valuable as the common currency of the diversity of life—but it must be integrated with other metrics to fully capture biodiversity. Because the multidimensionality of biodiversity poses formidable challenges to its measurement, a variety of surrogate or proxy measures are often used. These include the species richness of specific taxa, the number of distinct plant functional types (such as grasses, forbs, bushes, or trees), or the diversity of distinct gene sequences in a sample of microbial DNA taken from the soil. Species- or other taxon-based measures of biodiversity, however, rarely capture key attributes such as variability, function, quantity, and distribution—all of which provide insight into the roles of biodiversity. (See Box 1.2.)
Ecological indicators are scientific constructs that use quantitative data to measure aspects of biodiversity, ecosystem condition, services, or drivers of change, but no single ecological indicator captures all the dimensions of biodiversity (C2.2.4). (See Box 1.3.) Ecological indicators form a critical component of monitoring, assessment, and decision-making and are designed to communicate information quickly and easily to policy-makers. In a similar manner, economic indicators such as GDP are highly influential and well understood by decision-makers. Some environmental indicators, such as global mean temperature and atmospheric CO2 concentrations, are becoming widely accepted as measures of anthropogenic effects on global climate. Ecological indicators are founded on much the same principles and therefore carry with them similar pros and cons (C2.2.4). (See Box 1.4.)
Where Is Biodiversity?
Biodiversity is essentially everywhere, ubiquitous on Earth’s surface and in every drop of its bodies of water. The virtual omnipresence of life on Earth is seldom appreciated because most organisms are small (<5 centimeters); their presence is sparse, ephemeral, or cryptic, or, in the case of microbes, they are invisible to the unaided human eye (CF2).
Documenting spatial patterns in biodiversity is difficult because taxonomic, functional, trophic, genetic, and other dimensions of biodiversity have been relatively poorly quantified. Even knowledge of taxonomic diversity, the best known dimension of biodiversity, is incomplete and strongly biased toward the species level, megafauna, temperate systems, and components used by people. (See Figure 1.1.) This results in significant gaps in knowledge, especially regarding the status of tropical systems, marine and freshwater biota, plants, invertebrates, microorganisms, and subterranean biota. For these reasons, estimates of the total number of species on Earth range from 5 million to 30 million. Irrespective of actual global species richness, however, it is clear that the 1.7–2 million species that have been formally identified represent only a small portion of total species richness. More-complete biotic inventories are badly needed to correct for this deficiency (C4).
Spatial Patterns of Biodiversity: Hotspots, Biomes,[1] Biogeographic Realms, Ecosystems, and Ecoregions
While the data to hand are often insufficient to provide accurate pictures of the extent and distribution of all components of biodiversity, there are, nevertheless, many patterns and tools that decision-makers can use to derive useful approximations for both terrestrial and marine ecosystems. North-temperate regions often have usable data on spatial distributions of many taxa, and some groups (such as birds, mammals, reptiles, plants, butterflies, and dragonflies) are reasonably well documented globally. Biogeographic principles (such as gradients in species richness associated with latitude, temperature, salinity, and water depth) or the use of indicators can supplement available biotic inventories. Global and sub-global maps of species richness, several of which are provided in the MA reports Current State and Trends and Scenarios, provide valuable pictures of the distribution of biodiversity (C4, S10).
| 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:
Finally, the importance of variability and quantity varies, depending on the level of biodiversity measured. (See Table.)  |
Most macroscopic organisms have small, often clustered geographical ranges, leading to centers of both high diversity and endemism, frequently concentrated in isolated or topographically variable regions (islands, mountains, peninsulas). A large proportion of the world’s terrestrial biodiversity at the species level is concentrated in a small part of the world, mostly in the tropics. Even among the larger and more mobile species, such as terrestrial vertebrates, more than one third of all species have ranges of less than 1,000 square kilometers. In contrast, local and regional diversity of microorganisms tends to be more similar to large-scale and global diversity because of their large population size, greater dispersal, larger range sizes, and lower levels of regional species clustering (C4.2.3).
Biomes and biogeographic realms provide broad pictures of the distribution of functional diversity. Functional diversity (the variety of different ecological functions in a community independent of its taxonomic diversity) shows patterns of associations (biota typical of wetlands, forests, grasslands, estuaries, and so forth) with geography and climate known as biomes (see Figure 1.2), with ecosystems and ecoregions being smaller divisions within biomes (see Figure 1.3). These can be used to provide first-order approximations of both expected functional diversity as well as possible changes in the distribution of these associations should environmental conditions change.
| 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:
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.” |
| Box 1.4. Criteria for Effective Ecological Indicators |
An effective ecological indicator should:
|
Temporal Patterns of Biodiversity: Background Rates of Extinction and Biodiversity Loss
Knowledge of patterns of biodiversity over time allow for only very approximate estimates of background rates of extinction or of how fast species have become extinct over geological time. Except for the last 1,000 years, global biodiversity has been relatively constant over most of human history, but the history of life is characterized by considerable change. The estimated magnitude of background rates of extinction is roughly 0.1–1.0 extinctions per million species per year. Most measurements of this rate have come from assessing the length of species’ lifetimes through the fossil record: these range over 0.5–13 million years, and possibly 0.2–16 million years. These data probably underestimate background extinction rates because they are necessarily largely derived from taxa that are abundant and widespread in the fossil record (C4.4.2). Current rates of extinction are discussed in Key Question 3.
A mismatch exists between the dynamics of changes in natural systems and human responses to those changes. This mismatch arises from the lags in ecological responses, the complex feedbacks between socioeconomic and ecological systems, and the difficulty of predicting thresholds. Multiple impacts (especially the addition of climate change to the mix of forcing functions) can cause thresholds, or rapid and dramatic changes in ecosystem function even though the increase in environmental stress has been small and constant over time. Understanding such thresholds requires having long-term records, but such records are usually lacking or monitoring has been too infrequent, of the wrong periodicity, or too localized to provide the necessary data to analyze and predict threshold behavior (C28, S3.3.1).
Shifts to different regimes may cause rapid substantial changes in biodiversity, ecosystem services, and human well-being. Regime shifts have been commonly documented in pelagic systems due to thresholds related to temperature regimes and overexploitation (C19.2.1, C18). Some regime shifts are essentially irreversible, such as coral reef ecosystems that undergo sudden shifts from coral-dominated to algal-dominated reefs (C19.5). The trigger for such phase shifts usually includes increased nutrient inputs leading to eutrophic conditions and removal of herbivorous fishes that maintain the balance between corals and algae. Once the thresholds (both an upper and a lower threshold) for the two ecological processes of nutrient loading and herbivory are passed, the phase shift occurs quickly (within months), and the resulting ecosystem—though stable—is less productive and less diverse. Consequently, human well-being is affected not only by reductions in food supply and decreased income from reef-related industries (diving and snorkeling, aquarium fish collecting, and so on), but also by increased costs due to diminished ability of reefs to protect shorelines. (Algal reefs are more prone to being broken up in storm events, leading to shoreline erosion and seawater breaches of land) (C19.3). Such phase shifts have been documented in Jamaica, elsewhere in the Caribbean, and in Indo-Pacific reefs (C19, S3.3.1).
Introduced invasive species can act as a trigger for dramatic changes in ecosystem structure, function, and delivery of services. For example, the introduction of the carnivorous ctenophore Mnemiopsis leidyi (a jellyfish-like animal) in the Black Sea caused the loss of 26 major fisheries species and has been implicated (along with other factors) in the subsequent growth of the oxygen-deprived “dead” zone (C19.2.1).
Biodiversity and Its Link to Ecosystem Services
Biodiversity plays an important role in ecosystem functions that provide supporting, provisioning, regulating, and cultural services. These services are essential for human well-being. However, at present there are few studies that link changes in biodiversity with changes in ecosystem functioning to changes in human well-being. Protecting the Catskill watersheds that provide drinking water for New York City is one case where safeguarding ecosystem services paid a dividend of several billion dollars. Further work that demonstrates the links between biodiversity, regulating and supporting services, and human well-being is needed to show this vital but often unappreciated value of biodiversity (C4, C7, C11).
Species composition matters as much or more than species richness when it comes to ecosystem services. Ecosystem functioning, and hence ecosystem services, at any given moment in time is strongly influenced by the ecological characteristics of the most abundant species, not by the number of species. The relative importance of a species to ecosystem functioning is determined by its traits and its relative abundance. For example, the traits of the dominant or most abundant plant species—such as how long they live, how big they are, how fast they assimilate carbon and nutrients, how decomposable their leaves are, or how dense their wood is—are usually the key species drivers of an ecosystem’s processing of matter and energy. Thus conserving or restoring the composition of biological communities, rather than simply maximizing species numbers, is critical to maintaining ecosystem services (C11.2.1, C11.3).
Local or functional extinction, or the reduction of populations to the point that they no longer contribute to ecosystem functioning, can have dramatic impacts on ecosystem services. Local extinctions (the loss of a species from a local area) and functional extinctions (the reduction of a species such that it no longer plays a significant role in ecosystem function) have received little attention compared with global extinctions (loss of all individuals of a species from its entire range). Loss of ecosystem functions, and the services derived from them, however, occurs long before global extinction. Often, when the functioning of a local ecosystem has been pushed beyond a certain limit by direct or indirect biodiversity alterations, the ecosystem-service losses may persist for a very long time (C11).
Changes in biotic interactions among species—predation, parasitism, competition, and facilitation—can lead to disproportionately large, irreversible, and often negative alterations of ecosystem processes. In addition to direct interactions, such as predation, parasitism, or facilitation, the maintenance of ecosystem processes depends on indirect interactions as well, such as a predator preying on a dominant competitor such that the dominant is suppressed, which permits subordinate species to coexist. Interactions with important consequences for ecosystem services include pollination; links between plants and soil communities, including mycorrhizal fungi and nitrogen-fixing microorganisms; links between plants and herbivores and seed dispersers; interactions involving organisms that modify habitat conditions (beavers that build ponds, for instance, or tussock grasses that increase fire frequency); and indirect interactions involving more than two species (such as top predators, parasites, or pathogens that control herbivores and thus avoid overgrazing of plants or algal communities) (C11.3.2).
Many changes in ecosystem services are brought about by the removal or introduction of organisms in ecosystems that disrupt biotic interactions or ecosystem processes. Because the network of interactions among species and the network of linkages among ecosystem processes are complex, the impacts of either the removal of existing species or the introduction of new species are difficult to anticipate (C11). (See Table 1.1.)
As in terrestrial and aquatic communities, the loss of individual species involved in key interactions in marine ecosystems can also influence ecosystem processes and the provisioning of ecological services. For example, coral reefs and the ecosystem services they provide are directly dependent on the maintenance of some key interactions between animals and algae. As one of the most species-rich communities on Earth, coral reefs are responsible for maintaining a vast storehouse of genetic and biological diversity. Substantial ecosystem services are provided by coral reefs—such as habitat construction, nurseries, and spawning grounds for fish; nutrient cycling and carbon and nitrogen fixing in nutrient-poor environments; and wave buffering and sediment stabilization. The total economic value of reefs and associated services is estimated as hundreds of millions of dollars. Yet all coral reefs are dependent on a single key biotic interaction: symbiosis with algae. The dramatic effects of climate change and variability (such as El Niño oscillations) on coral reefs are mediated by the disruption of this symbiosis (C11.4.2).
Supporting Services
Biodiversity affects key ecosystem processes in terrestrial ecosystems such as biomass production, nutrient and water cycling, and soil formation and retention—all of which govern and ensure supporting services (high certainty). The relationship between biodiversity and supporting ecosystem services depends on composition, relative abundance, functional diversity, and, to a lesser extent, taxonomic diversity. If multiple dimensions of biodiversity are driven to very low levels, especially trophic or functional diversity within an ecosystem, both the level and stability (for instance, biological insurance) of supportive services may decrease (CF2, C11). (See Figure 1.4.)
Region-to-region differences in ecosystem processes are driven mostly by climate, resource availability, disturbance, and other extrinsic factors and not by differences in species richness (high certainty). In natural ecosystems, the effects of abiotic and land use drivers on ecosystem services are usually more important than changes in species richness. Plant productivity, nutrient retention, and resistance to invasions and diseases sometimes grow with increasing species numbers in experimental ecosystems that have been reduced to low levels of biodiversity. In natural ecosystems, however, these direct effects of increasing species richness are usually overridden by the effects of climate, resource availability, or disturbance regime (C11.3).
Even if losses of biodiversity have small short-term impacts on ecosystem function, such losses may reduce the capacity of ecosystems for adjustment to changing environments (that is, ecosystem stability or resilience, resistance, and biological insurance) (high certainty). The loss of multiple components of biodiversity, especially functional and ecosystem diversity at the landscape level, will lead to lowered ecosystem stability (high certainty). Although the stability of an ecosystem depends to a large extent on the characteristics of the dominant species (such as life span, growth rate, or regeneration strategy), less abundant species also contribute to the long-term preservation of ecosystem functioning. There is evidence that a large number of resident species, including those that are rare, may act as “insurance” that buffers ecosystem processes in the face of changes in the physical and biological environment (such as changes in precipitation, temperature, pathogens) (C11.3.2). As tragically illustrated by social conflict and humanitarian crisis over droughts, floods, and other ecosystem collapses, stability of ecosystems underpins most components of human well-being, including health, security, satisfactory social relations, and freedom of choice and action (C6; see also Key Question 2).
Regulating Services
Invasion resistance
The preservation of the number, types, and relative abundance of resident species can enhance invasion resistance in a wide range of natural and semi-natural ecosystems (medium certainty). Although areas of high species richness (such as biodiversity hot spots) are more susceptible to invasion than species-poor areas, within a given habitat the preservation of its natural species pool appears to increase its resistance to invasions by non-native species. This is also supported by evidence from several marine ecosystems, where decreases in the richness of native taxa were correlated with increased survival and percent cover of invading species (C11.3.1, C11.4.1).
Pollination
Pollination is essential for the provision of plant-derived ecosystem services, yet there have been worldwide declines in pollinator diversity (medium certainty). Many fruits and vegetables require pollinators, thus pollination services are critical to the production of a considerable portion of the vitamins and minerals in the human diet. Although there is no assessment at the continental level, documented declines in more-restricted geographical areas include mammals (lemurs and bats, for example) and birds (hummingbirds and sunbirds, for instance), bumblebees in Britain and Germany, honeybees in the United States and some European countries, and butterflies in Europe. The causes of these declines are multiple, but habitat destruction and the use of pesticide are especially important. Estimates of the global annual monetary value of pollination vary widely, but they are in the order of hundreds of billions of dollars (C11.3.2, Box C11.2).
Climate regulation
Biodiversity influences climate at local, regional, and global scales, thus changes in land use and land cover that affect biodiversity can affect climate. The important components of biodiversity include plant functional diversity and the type and distribution of habitats across landscapes. These influence the capacity of terrestrial ecosystems to sequester carbon, albedo (proportion of incoming radiation from the Sun that is reflected by the land surface back to space), evapotranspiration, temperature, and fire regime—all of which influence climate, especially at the landscape, ecosystem, or biome levels. For example, forests have higher evapotranspiration than other ecosystems, such as grasslands, because of their deeper roots and greater leaf area. Thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems. In the Amazon, for example, 60% of precipitation comes from water transpired by upwind ecosystems (C11.3.3).
In addition to biodiversity within habitats, the diversity of habitats in a landscape exerts additional impacts on climate across multiple scales. Landscape-level patches (>10 kilometers in diameter) that have lower albedo and higher surface temperature than neighboring patches create cells of rising warm air above the patch (convection). This air is replaced by cooler moister air that flows laterally from adjacent patches (advection). Climate models suggest that these landscape-level effects can substantially modify local-to-regional climate. In Western Australia, for example, the replacement of native heath vegetation by wheatlands increased regional albedo. As a result, air tended to rise over the dark (more solar-absorptive and therefore warmer) heathland, drawing moist air from the wheatlands to the heathlands. The net effect was a 10% increase in precipitation over heathlands and a 30% decrease in precipitation over croplands (C11.3.3).
Some components of biodiversity affect carbon sequestration and thus are important in carbon-based climate change mitigation when afforestation, reforestation, reduced deforestation, and biofuel plantations are involved (high certainty). Biodiversity affects carbon sequestration primarily through its effects on species characteristics, which determine how much carbon is taken up from the atmosphere (assimilation) and how much is released into it (decomposition, combustion). Particularly important are how fast plants can grow, which governs carbon inputs, and woodiness, which enhances carbon sequestration because woody plants tend to contain more carbon, live longer, and decompose more slowly than smaller herbaceous plants. Plant species also strongly influence carbon loss via decomposition and their effects on disturbance. Plant traits also influence the probability of disturbances such as fire, windthrow, and human harvest, which temporarily change forests from accumulating carbon to releasing it (C11.3.3).
The major importance of marine biodiversity in climate regulation appears to be via its effect on biogeochemical cycling and carbon sequestration. The ocean, through its sheer volume and links to the terrestrial biosphere, plays a huge role in cycling of almost every material involved in biotic processes. Of these, the anthropogenic effects on carbon and nitrogen cycling are especially prominent. Biodiversity influences the effectiveness of the biological pump that moves carbon from the surface ocean and sequesters it in deep waters and sediments. Some of the carbon that is absorbed by marine photosynthesis and transferred through food webs to grazers sinks to the deep ocean as fecal pellets and dead cells. The efficiency of this trophic transfer and therefore the extent of carbon sequestration is sensitive to the species richness and composition of the plankton community (C11.4.3).
Pest, disease, and pollution control
The maintenance of natural pest control services, which benefits food security, rural household incomes, and national incomes of many countries, is strongly dependent on biodiversity. Yields of desired products from agroecosystems may be reduced by attacks of animal herbivores and microbial pathogens, above and below ground, and by competition with weeds. Increasing associated biodiversity with low-diversity agroecosystems, however, can enhance biological control and reduce the dependency and costs associated with biocides. Moreover, high-biodiversity agriculture has cultural and aesthetic value and can reduce many of the externalized costs of irrigation, fertilizer, pesticide, and herbicide inputs associated with monoculture agriculture (C11.3.4, Boxes C11.3 and C11.4).
The marine microbial community provides critical detoxification services, but how biodiversity influences them is not well understood. There is very little information on how many species are necessary to provide detoxification services, but these services may critically depend on one or a few species. Some marine organisms provide the ecosystem service of filtering water and reducing effects of eutrophication. For example, American oysters in Chesapeake Bay were once abundant but have sharply declined—and with them, their filtering ecosystem services. Areas like the Chesapeake might have much clearer water if large populations of filtering oysters could be reintroduced. Some marine microbes can degrade toxic hydrocarbons, such as those in an oil spill, into carbon and water, using a process that requires oxygen. Thus this service is threatened by nutrient pollution, which generates oxygen deprivation (C11.4.4).
Why is biodiversity loss a concern?
- Biodiversity is essential for ecosystem services and hence for human well-being. Biodiversity goes beyond the provisioning for material welfare and livelihoods to include security, resiliency, social relations, health, and freedoms and choices. Some people have benefited over the last century from the conversion of natural ecosystems to human-dominated ecosystems and from the exploitation of biodiversity. At the same time, however, these losses in biodiversity and associated changes in ecosystem services have caused other people to experience declining well-being, with some social groups being pushed into poverty.
Main Links among Biodiversity, Ecosystem Services, and Various Constituents of Human Well-being
The MA identifies biodiversity and the many ecosystem services that it provides as a key instrumental and constitutive factor determining human well-being. The MA findings support, with high certainty, that biodiversity loss and deteriorating ecosystem services contribute—directly or indirectly—to worsening health, higher food insecurity, increasing vulnerability, lower material wealth, worsening social relations, and less freedom for choice and action.
Food Security
Biological diversity is used by many rural communities directly as an insurance and coping mechanism to increase flexibility and spread or reduce risk in the face of increasing uncertainty, shocks, and surprises. The availability of this biological “safety net” has increased the security and resilience of some local communities to external economic and ecological perturbations, shocks, or surprises (C6.2.2, C8.2). In a world where fluctuating commodity prices are more the norm than the exception, economic entitlements of the poor are increasingly becoming precarious. The availability of an ecosystem-based food security net during times when economic entitlements are insufficient to purchase adequate nourishment in the market provides an important insurance program (C8.1, C6.7).
Coping mechanisms based on indigenous plants are particularly important for the most vulnerable people, who have little access to formal employment, land, or market opportunities (C6). For example, investigations of two dryland sites in Kenya and Tanzania report local communities using wild indigenous plants to provide alternative sources of food when harvests failed or when sudden expenses had to be met (such as a hospital bill). (See Table 2.1.)
Another pathway through which biodiversity can improve food security is the adoption of farming practices that maintain and make use of agricultural biodiversity. Biodiversity is important to maintaining agricultural production. Wild relatives of domestic crops provide genetic variability that can be crucial for overcoming outbreaks of pests and pathogens and new environmental stresses. Many agricultural communities consider increased local diversity a critical factor for the long-term productivity and viability of their agricultural systems. For example, interweaving multiple varieties of rice in the same paddy has been shown to increase productivity by lowering the loss from pests and pathogens.
Vulnerability
The world is experiencing an increase in human suffering and economic losses from natural disasters over the past several decades. Mangrove forests and coral reefs—a rich source of biodiversity—are excellent natural buffers against floods and storms. Their loss or reduction in coverage has increased the severity of flooding on coastal communities. Floods affect more people (140 million per year on average) than all other natural or technological disasters put together. Over the past four decades, the number of “great” disasters has increased by a factor of four, while economic losses have increased by a factor of ten. During the 1990s, countries low on the Human Development Index experienced about 20% of the hazard events and reported over 50% of the deaths and just 5% of economic losses. Those with high rankings on the index accounted for over 50% of the total economic losses and less than 2% of the deaths (C6, R11, C16).
A common finding from the various sub-global assessments was that many people living in rural areas cherish and promote ecosystem variability and diversity as a risk management strategy against shocks and surprises (SG11). They maintain a diversity of ecosystem services and are skeptical about solutions that reduce their options. The sub-global assessments found that diversity of species, food, and landscapes serve as “savings banks” that rural communities use to cope with change and ensure sustainable livelihoods (see Peruvian, Portuguese, Costa Rican, and India sub-global assessments).
Health
An important component of health is a balanced diet. About 7,000 species of plants and several hundred species of animals have been used for human food consumption at one time or another. Some indigenous and traditional communities currently consume 200 or more species. Wild sources of food remain particularly important for the poor and landless to provide a somewhat balanced diet (C6, C8.2.2). Overexploitation of marine fisheries worldwide, and of bushmeat in many areas of the tropics, has lead to a reduction in the availability of wild-caught animal protein, with serious consequences in many countries for human health (C4.3.4).
Human health, particularly risk of exposure to many infectious diseases, may depend on the maintenance of biodiversity in natural ecosystems. On the one hand, a greater diversity of wildlife species might be expected to sustain a greater diversity of pathogens that can infect humans. However, evidence is accumulating that greater wildlife diversity may decrease the spread of many wildlife pathogens to humans. The spread of Lyme disease, the best-studied case, seems to be decreased by the maintenance of the biotic integrity of natural ecosystems (C11, C14).
Energy Security
Wood fuel provides more than half the energy used in developing countries. Even in industrial countries such as Sweden and the United States, wood supplies 17% and 3% of total energy consumption respectively. In some African countries, such as Tanzania, Uganda, and Rwanda, wood fuel accounts for 80% of total energy consumption (SG-SAfMA). In rural areas, 95% is consumed in the form of firewood, while in urban areas 85% is in the form of charcoal. Shortage of wood fuel occurs in areas with high population density without access to alternative and affordable energy sources. In some provinces of Zambia where population densities exceed the national average of 13.7 persons per square kilometer, the demand for wood has already surpassed local supply. In such areas, people are vulnerable to illness and malnutrition because of the lack of resources to heat homes, cook food, and boil water. Women and children in rural poor communities are the ones most affected by wood fuel scarcity. They must walk long distances searching for firewood and therefore have less time for tending crops and school (C9.4).
Provision of Clean Water
The continued loss of cloud forests and the destruction of watersheds reduce the quality and availability of water supplied to household use and agriculture. The availability of clean drinking water is a concern in dozens of the world’s largest cities (C27). In one of the best documented cases, New York City took steps to protect the integrity of watersheds in the Catskills to ensure continued provision of clean drinking water to 9 million people. Protecting the ecosystem was shown to be far more cost-effective than building and operating a water filtration plant. New York City avoided $6–8 billion in expenses by protecting its watersheds (C7, R17).
Social Relations
Many cultures attach spiritual and religious values to ecosystems or their components such as a tree, hill, river, or grove (C17). Thus loss or damage to these components can harm social relations—for example, by impeding religious and social ceremonies that normally bind people. (See Box 2.1.) Damage to ecosystems, highly valued for their aesthetic, recreational, or spiritual values can damage social relations, both by reducing the bonding value of shared experience as well as by causing resentment toward groups that profit from their damage (S11, SG10).
| Box 2.1. Social Consequences of Biodiversity Degradation (SG-SAfMA) |
| The basic needs of the AmaXhosa people in South Africa are met by ecosystem services, including fuelwood, medicinal plants, building materials, cultural species, food supplements, and species of economic value. When asked by researchers about their relationship with the natural environment, a local responded “I am entirely dependent on the environment. Everything that I need comes from this environment” and “[the environment] will be important forever because if you have something from the environment it does encourage you to love the environment.” Respondents often described positive emotional and physical symptoms when the environment is healthy: “When the environment is healthy, my body and spirit is also happy.” And when describing people’s feelings toward a healthy environment, a respondent stated that “people love such an environment. They really adore it. Such an environment makes them feel free.” In addition, respondents described the feelings of peace when walking in the bush and how they would go into the natural environment to pray. The beliefs and traditions of the AmaXhosa play an important role in guiding resource use and management and encouraging values to be place-centered. The ancestors are central to this cosmology, where the very identity of a Xhosa person is based on performing traditions and rituals for ancestors. The majority of respondents stated that practicing traditions and thus communicating with ancestors is what is of value to a Xhosa person. A number of sites and species are fundamental to the performance of rituals and maintaining a relationship with the ancestors. When respondents were asked what would happen if these sites were to be destroyed, they replied “It means that the ancestors would be homeless.” “That can’t happen here at this village because our health depends entirely on these sites,” and “it means that our culture is dead.” |
Freedom of Choice and Action
Freedom of choice and action within the MA context refers to individuals having control over what happens and being able to achieve what they value (CF3). Loss of biodiversity often means a loss of choices. Local fishers depend on mangroves as breeding grounds for local fish populations. Loss of mangroves translates to a loss in control over the local fish stock and a livelihood they have been pursuing for many generations and that they value. Another example is high-diversity agricultural systems. These systems normally produce less cash than monoculture cash crops, but farmers have some control over their entitlements because of spreading risk through diversity. High diversity of genotypes, populations, species, functional types, and spatial patches decreases the negative effects of pests and pathogens on crops and keeps open possibilities for agrarian communities to develop crops suited to future environmental challenges and to increase their resilience to climate variability and market fluctuations (C11).
Another dimension of choices relates to the future. The loss of biodiversity in some instances is irreversible, and the value individuals place on keeping biodiversity for future generations—the option value—can be significant (CF6, C2). The notion of having choices available irrespective of whether any of them will be actually picked is an essential constituent of the freedom aspect of well-being. However, putting a monetary figure on option values is notoriously difficult. We can only postulate on the needs and desires of future generations, some of which can be very different from today’s aspirations.
Basic Materials for a Good Life and Sustainable Livelihoods
Biodiversity offers directly the various goods—often plants, animals, and fungi—that individuals need in order to earn an income and secure sustainable livelihoods. In addition, it also contributes to livelihoods through the support it provides for ecosystem services: the agricultural labor force currently contains approximately 22% of the world’s population and accounts for 46% of its total labor force (C26.5.1). For example, apples are a major cash crop in the Himalayan region in India, accounting for 60–80% of total household income (SG3). The region is also rich in honeybee diversity, which played a significant role in pollinating field crops and wild plants, thereby increasing productivity and sustaining ecosystem functions. In the early 1980s, market demand for particular types of apples led farmers to uproot pollinated varieties and plant new, sterile cultivars. The pollinator populations were also negatively affected by excessive use of pesticides. The result was a reduction in overall apple productivity and the extinction of many natural pollinator species (SG3).
Nature-based tourism (“ecotourism”)—one of the fastest-growing segments of tourism worldwide—is a particularly important economic sector in a number of countries and a potential income source for many rural communities (C17.2.6). The aggregate revenue generated by nature-based tourism in Southern Africa was estimated to be $3.6 billion in 2000, roughly 50% of total tourism revenue (SG-SAfMA). Botswana, Kenya, Namibia, South Africa, Tanzania, Uganda, and Zimbabwe each generated over $100 million in revenue annually from nature-based tourism in 2000. In Tanzania, tourism contributed 30% of the total GDP of the country.
Biodiversity also contributes to a range of other industries, including pharmaceuticals, cosmetics, and horticulture. Market trends vary widely according to the industry and country involved but many bioprospecting activities and revenues are expected to increase over the next decades (C10). The current economic climate suggests that pharmaceutical bioprospecting will increase, especially as new methods use evolutionary andecological knowledge.
Losses of biodiversity can impose substantial costs at local and national scales. For example, the collapse of the Newfoundland cod fishery in the early 1990s cost tens of thousands of jobs, as well as at least $2 billion in income support and retraining. Recent evidence suggests that the preservation of the integrity of local biological communities, both in terms of the identity and the number of species, is important for the maintenance of plant and animal productivity, soil fertility, and their stability in the face of a changing environment (C11). Recent estimates from the MA Portugal sub-global assessment indicate that environmental expenses in that country are increasing at a rate of 3% a year and are presently 0.7% of GDP (SG-Portugal).
Trade-offs among Biodiversity, Ecosystem Services, and Human Well-being
When society has multiple goals, many of which depend on biodiversity, ecosystem services, and the many constituents of well-being, difficult decisions involving trade-offs among competing goals have to be made. The value of ecosystem services lost to human society, in the long term, may greatly exceed the short-term economic benefits that are gained from transformative activities. In Sri Lanka, for example, the clearing of tropical forest for agriculture initially reduced the habitat for forest-adapted anopheline mosquito vectors of malaria. But in due course, other vector species occupied the changed habitat, contributing to the resurgence of malaria (SG3).
Many of the changes in biodiversity and ecosystems have been made to enhance the production of specific ecosystem services such as food production. But only 4 of the 24 ecosystem services examined in this assessment have been enhanced: crops, livestock, aquaculture, and (in recent decades) carbon sequestration, while 15 services have been degraded. (See Table 2.2.) The degraded services include capture fisheries, timber production, water supply, waste treatment and detoxification, water purification, natural hazard protection, regulation of air quality, regulation of regional and local climate, regulation of erosion, and many cultural services (the spiritual, aesthetic, recreational, and other benefits of ecosystems). Modifications of ecosystems to enhance one service generally have come at a cost to other services that the ecosystem provided. For example, while the expansion of agriculture and its increased productivity are a success story of enhanced production of one key ecosystem service, this success has come at high and growing costs in terms of trade-offs with other ecosystem services, both through the direct impact of land cover change and as a result of water withdrawals for irrigation and release of nutrients into rivers. Globally, roughly 15–35% of irrigation withdrawals are estimated to be unsustainable (low to medium uncertainty).The impacts of these trade-offs among ecosystem services affect people in different ways. An aquaculture farmer, for instance, may gain material welfare from management practices that increase soil salinization and thereby reduce rice yields and threaten food security for nearby subsistence farmers.
Trade-off analysis aided by qualitative and quantitative values for biodiversity and ecosystem services can help decision-makers make intelligent decisions among competing goals (R17). (See Figure 2.1.) Such analysis can identify management strategies that generate efficient outcomes in which it is not possible to increase one objective without decreasing another. Second, it can show the extent to which current decisions are inefficient and help identify opportunities for improving the status quo. Third, it illustrates the nature of the trade-offs between goals once the efficiency frontier has been reached.
Values of Biodiversity and Ecosystem Services for Human Well-being
The importance of biodiversity and natural processes in producing ecosystem services that people depend on is not captured in financial markets. Unlike goods bought and sold in markets, many ecosystem services do not have markets or readily observable prices. However, lack of a price does not mean lack of value. A substantial body of research on nonmarket valuation is now available for some ecosystem services, including clean drinking water, recreation, or commercially harvested species. Existence value of species and other “non-use” values pose a greater challenge to those who would try to measure the complete value of conserving biodiversity and natural processes. The fact that ecosystems are dynamic and complex, as well as the fact that human preferences change through time, also present difficulties for attempts to value natural systems. Combinations of irreversible actions, such as species extinction, and uncertainty give rise to option value (such as the value of maintaining flexibility, keeping options open, until uncertainty is resolved). Though clear in theory, getting reasonable estimates of option value is difficult in practice (C2.3). Better quantification of the benefits derived from ecosystems would provide greater impetus for biodiversity protection and create a more transparent picture of the equitability of the distribution of benefits.
Private and social values of conserving biodiversity and natural systems often differ widely. The private use value of biodiversity and ecosystem services by individuals will typically ignore the “external” benefits of conservation that accrue to society in general. For example, a farmer may benefit from intensive use of the land but generally does not bear all the consequences caused by leaching of excess nutrients and pesticides into ground or surface water, or the consequences of loss of habitat for native species. If private decision-makers are not given the incentives to value the larger social benefits of conservation, their decisions will often result in inadequate conservation (C5.4).
The indirect values of biodiversity conservation can be highly significant in comparison with the direct economic values derived from a particular area. (See Box 2.2.) In existing economic studies of changes to biodiversity in specific locations (such as the conversion of mangrove forests, degradation of coral reefs, and clear-felling of forests), the costs of ecosystem conversion are often found to be significant and sometimes exceed the benefits of the habitat conversion. Despite this, in a number of these cases conversion was promoted because the value of the lost ecosystem services—the indirect value of biodiversity conservation—was not internalized. In other instances, subsidies distorted the relative costs and benefits and provided the incentives to destroy biodiversity (C5).
| Box 2.2. Economic Costs and Benefits of Ecosystem Conversion (C5 Box 5.2) |
| Relatively few studies have compared the total economic value of ecosystems under alternate management regimes. The results of several that attempted to do so are shown in the Figure. In each case where the total economic value of sustainable management practices was compared with management regimes involving conversion of the ecosystem or unsustainable practices, the benefit of managing the ecosystem more sustainably exceeded that of the converted ecosystem even though the private benefits—that is, the actual monetary benefits captured from the services entering the market—would favor conversion or unsustainable management. These studies are consistent with the understanding that market failures associated with ecosystem services lead to greater conversion of ecosystems than is economically justified. However, this finding would not hold at all locations. For example, the value of conversion of an ecosystem in areas of prime agricultural land or in urban regions often exceeds the total economic value of the intact ecosystem (although even in dense urban areas, the TEV of maintaining some “green space” can be greater than development of these sites) (C5). 
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The depletion and degradation of many ecosystem services represents the loss of a capital asset that is poorly reflected in conventional indicators of economic growth or growth in human well-being (C2.3.5). A country could cut its forests and deplete its fisheries, and this would show only as a positive gain to GDP, despite the loss of the capital asset. (GDP measures the flow of economic benefits from the use of these resources, but the depletion of the capital asset is not reflected.) Moreover, many ecosystem services are available freely to those who use them (fresh water in aquifers, for instance, and the use of the atmosphere as a sink for pollutants) and so again their degradation is not reflected in standard economic measures. When changes to these natural capital assets are factored into measures of the inclusive wealth of nations, they significantly change the balance sheet for countries with economies largely dependent on natural resources. Some countries that appeared to have positive growth in the 1970s and 1980s, for example, actually experienced a net loss of capital assets, effectively undermining the sustainability of any gains they may have achieved.
The Distributional Impacts of Biodiversity Loss and Ecosystem Change
Biodiversity use, change, and loss have improved well-being for many social groups and individuals. But people with low resilience to ecosystem changes—mainly the disadvantaged—have been the biggest losers and witnessed the biggest increase in not only monetary poverty but also relative, temporary poverty and the depth of poverty (C5, C6, R17). See Box 2.3 for a description of various types of poverty.
| Box 2.3. Concepts and Measures of Poverty |
| Relative poverty is the state of deprivation defined by social standards. It is fixed by a contrast with others in the society who are not considered poor. Poverty is then seen as lack of equal opportunities. It is based on subjective measures of poverty. Depth of poverty is a measure of the average income gap of the poor in relation to a certain threshold. It defines how poor the poor are. It gives the amount of resources needed to bring all poor people to the poverty-line level. Temporary poverty is characterized by a short-term deprivation, usually seasonal, of water or food. Monetary poverty is an insufficiency of income or monetary resources. Most indicators like the U.S. dollar a day indicator or national poverty lines are defined in those terms. Multidimensional poverty is conceived as a group of irreducible deprivations that cannot be adequately expressed as income insufficiency. It combines basic constituents of well-being in a composite measure, such as the Human Poverty Index. Other characteristics of poverty commonly used in the literature include rural and urban poverty, extreme poverty (or destitution), female poverty (to indicate gender discrimination), and food-ratio poverty lines (with calorie-income elasticities). Other indices such as the FGT (Foster, Greer, and Thorbecke) or the Sen Index, which combine both dimensions of incidence and depth of poverty, are also widely used. The type of poverty experienced by individuals will therefore differ for different rates and levels of biodiversity and ecosystem services loss and if the loss is transitory or permanent. |
Many communities depend on a range of biological products for their material welfare. In addition, the transfer of ownership or use rights to ecosystem services like timber, fishing, and mining to privileged groups by governments have also excluded local communities from the use of these ecosystem services (R8). Provisions for ensuring the equitable distribution of monetary benefits from the use of biological products are an issue of major concern. Even in cases where equitable provisioning has been made, implementation is being impaired by weak and ineffective institutions (C10).
Poor people have historically disproportionately lost access to biological products and ecosystem services as demand for those services has grown. Coastal habitats are often converted to other uses, frequently for aquaculture ponds or cage culturing of highly valued species such as shrimp and salmon. Despite the fact that the area is still used for food production, local residents are often displaced from their fishing grounds, and the fish produced are usually not for local consumption but for export. Coastal residents often no longer have access to cheap protein or sources of income (C18). The development of shrimp aquaculture has displaced local fishers who are not able to enter the capital- and technology-intensive shrimp fisheries (SG3). Food security and overall well-being is much better in situations where local communities—with particular focus on the poor and the disadvantaged—were involved and made partners in the access, use, and management of biodiversity.
Changes in the equity structure of societies can have impacts on ecosystem services. Differential access to resources may also help to explain why some people living in environmental resource-rich areas nevertheless rank low in measures of human well-being. For example, economic liberalization in Viet Nam resulted in the development of a class of entrepreneurs with markedly greater access to capital. The poorer fishers were unable to enter the capital and technology-intensive shrimp fishery that developed. Furthermore, the ecological changes precipitated by the expansion of shrimp aquaculture reduced the capacity of the ecosystem to support the traditional fish stocks, further exacerbating the inequity (SG3.7).
The increase in international trade of biological products has improved the well-being for many social groups and individuals, especially in countries with well-developed markets and trade rules and among people in developing countries who have access to the biological products. However, many groups have not benefited from such trade. Some people who live near and are dependent on biodiversity-rich areas have experienced a drop in their well-being rather than an increase. Examples include the many indigenous groups and local communities who have relied on these products and the ecosystem services they support for many of the constituents of well- being. Weak and inefficient institutional structures that oversee the equitable distribution of benefits are key reasons for the inequitable distribution of benefits at the national and local levels. In addition, structural adjustment programs played a key role in pushing the poor further into destitution and forcing many to have no choice but to further stress ecosystem services (R17).
Conflicts between competing social groups or individuals over access to and use of biological products and ecosystem services have contributed to declines in well-being for some groups and improvements for others. Sometimes different social groups have a conflict over how a given bundle of ecosystem services or biological products ought to be used and shared. Although many such conflicts have been managed cooperatively, it is also common for one group to impose its preferred outcome on the others, leading to an improvement in well-being for one group at the expense of others. For example, if mountain communities convert forests into agricultural lands, they may reduce downstream water quality. When ecosystem change is linked to well-being change through this highly complex structure of interdependencies, there are both winners and losers. Some groups improve and other groups decline (C6). Box 2.4 describes some conflicts that emerged in Chile over the mining industry and local communities.
Box 2.4. Conflicts Between the Mining Sector and Local Communities in Chile |
The Salar de Atacama, Chile, is a salty wetland within the driest desert in the world. Surface water is limited. The present major concern is over groundwater usage and the extent to which the exploitation is sustainable. The economic activities in this region include mining, agriculture, and tourism, all of which depend on the quantity and quality of available water. The Salar de Atacama holds over 40% of world lithium reserves; mining provides 12% of local employment and two thirds of the regional GDP. It also consumes 65% of the water used in the region. Tourism is the second largest source of employment and income, and tourist facilities need fresh water. Local communities rely on water for subsistence agriculture and livestock raising. Most subsistence farmers do not have enough resources to buy water rights when bidding against the mining companies. Hence the shortage of water is generating major conflicts over access and ownership rights among competing users (SG.SDM). |
One of the main reasons some countries, social groups, or individuals—especially the disadvantaged—are more severely affected by biodiversity and ecosystem changes is limited access to substitutes or alternatives. When the quality of water deteriorates, the rich have the resources to buy personal water filters or imported bottled water that the poor can ill afford. Similarly, urban populations in developing countries have easier access to clean energy sources because of easy access to the electrical grid, while rural communities have fewer choices. Poor farmers often do not have the option of substituting modern methods for services provided by biodiversity because they cannot afford the alternatives. And, substitution of some services may not be sustainable, and may have negative environmental and human health effects. For example, the reliance on toxic and persistent pesticides to control certain pests can have negative effects on the provision of services by the cultivated system and other ecosystems connected to the cultivated system (C.26.2). Many industrial countries maintain seed banks in response to the rapid rate of loss of crop genetic diversity and to make existing genetic diversity more readily available to plant breeders. Apart from the network of seed banks maintained in developing countries by the Consultative Group on International Agricultural Research, for many developing countries creating such banks could pose a problem when electricity supplies are unreliable, fuel is costly, and there is a lack of human capacity (R17).
Place-based or micro-level data and not macro-level or aggregated data provide more useful information to identify disadvantaged communities being affected by biodiversity and ecosystem changes. Most poverty statistics are only available at an aggregate level. These tend to hide pockets of poverty existing sometimes within traditionally defined “wealthy” regions or provinces. Therefore, using aggregate data to understand and establish links between biodiversity loss, ecosystem changes, and well-being can be quite misleading (C5).
What are the current trends and drivers of biodiversity loss?
- Across the range of biodiversity measures, current rates of loss exceed those of the historical past by several orders of magnitude and show no indication of slowing.
- Biodiversity is declining rapidly due to land use change, climate change, invasive species, overexploitation, and pollution. These result from demographic, economic, sociopolitical, cultural, technological, and other indirect drivers.
- While these drivers vary in their importance among ecosystems and regions, current trends indicate a continuing loss of biodiversity.
Recent and Current Trends in Biodiversity
Across the range of biodiversity measures, current rates of change and loss exceed those of the historical past by several orders of magnitude and show no indication of slowing. At large scales, across biogeographic realms and ecosystems (biomes), declines in biodiversity are recorded in all parts of the habitable world. Among well-studied groups of species, extinction rates of organisms are high and increasing (medium certainty), and at local levels both populations and habitats are most commonly found to be in decline. (C4)
Virtually all of Earth’s ecosystems have now been dramatically transformed through human actions. More land was converted to cropland in the 30 years after 1950 than in the 150 years between 1700 and 1850 (C26). Between 1960 and 2000, reservoir storage capacity quadrupled (C7.2.4) and, as a result, the amount of water stored behind large dams is estimated to be three to six times the amount held by rivers (C7.3.2). Some 35% of mangroves have been lost in the last two decades in countries where adequate data are available (encompassing about half of the total mangrove area) (C19.2.1). Roughly 20% of the world’s coral reefs have been destroyed and an additional 20% have been degraded (C19.2.1). Although the most rapid changes in ecosystems are now taking place in developing countries, industrial countries historically experienced comparable changes.
The biomes with the highest rates of conversion in the last half of the 20th century were temperate, tropical, and flooded grasslands and tropical dry forests (more than 14% lost between 1950 and 1990) (C4.4.3). Areas of particularly rapid change in terrestrial ecosystems over the past two decades include (C28.2):
- the Amazon basin and Southeast Asia (deforestation and expansion of croplands);
- Asia (land degradation in drylands); and
- Bangladesh, Indus Valley, parts of Middle East and Central Asia, and the Great Lakes region of Eastern Africa.
Habitat conversion to agricultural use has affected all biogeographical realms. In all realms (except Oceania and Antarctica), at least a quarter of the area had been converted to other land uses by 1950 (C4.4.4), and in the Indo-Malayan realm almost half of the natural habitat cover had been converted. In the 40 years from 1950 to 1990, habitat conversion has continued in nearly all realms. (See Figure 3.1.) The temperate northern realms of the Nearctic and Palearctic are currently extensively cultivated and urbanized; however, the amount of land under cultivation and pasture seems to have stabilized in the Nearctic, with only small increases in the Palearctic in the last 40 years. The decrease in extensification of land under agricultural use in these areas is counterbalanced by intensification of agricultural practices in order to ensure continued food production for expanding human populations (C8, C26). Within the tropics, rates of land conversion to agricultural use range from very high in the Indo-Malayan realm to moderate in the Neotropics and the Afrotropics, where large increases in cropland area have taken place since the 1950s. Australasia has relatively low levels of cultivation and urbanization, but these have also increased in the last 40 years at a similar rate to those of the Neotropics.
The majority of biomes have been greatly modified. Between 20% and 50% of 9 out of 14 global biomes have been transformed to croplands. Tropical dry forests were the most affected by cultivation between 1950 and 1990, although temperate grasslands, temperate broadleaf forests, and Mediterranean forests each experienced 55% or more conversion prior to 1950. Biomes least affected by cultivation include boreal forests and tundra. (See Figure 3.2.) While cultivated lands provide many provisioning services (such as grains, fruits, and meat), habitat conversion to agriculture typically leads to reductions in local native biodiversity (C4.4.3).
Rates of human conversion among biomes have remained similar over at least the last century. For example, boreal forests had lost very little native habitat cover up to 1950 and have lost only a small additional percentage since then. In contrast, the temperate grasslands biome had lost nearly 70% of its native cover by 1950 and lost an additional 15.4% since then. Two biomes appear to be exceptions to this pattern: Mediterranean forests and temperate broadleaf forests. Both had lost the majority of their native habitats by 1950 but since then have lost less than 2.5% additional habitat. These biomes contain many of the world’s most established cities and most extensive surrounding agricultural development (Europe, the United States, the Mediterranean basin, and China). It is possible that in these biomes the most suitable land for agriculture had already been converted by 1950 (C4.4.3).
Over the past few hundred years, humans have increased the species extinction rate by as much as three orders of magnitude (medium certainty). This estimate is only of medium certainty because the extent of extinctions of undescribed taxa is unknown, the status of many described species is poorly known, it is difficult to document the final disappearance of very rare species, and there are extinction lags between the impact of a threatening process and the resulting extinction. However, the most definite information, based on recorded extinctions of known species over the past 100 years, indicates extinction rates are around 100 times greater than rates characteristic of species in the fossil record (C4.4.2). Other less direct estimates, some of which model extinctions hundreds of years into the future, estimate extinction rates 1,000 to 10,000 times higher than rates recorded among fossil lineages. (See Figure 3.3.)
Between 12% and 52% of species within well-studied higher taxa are threatened with extinction, according to the IUCN Red List. Less than 10% of named species have been assessed in terms of their conservation status. Of those that have, birds have the lowest percentage of threatened species, at 12%. The patterns of threat are broadly similar for mammals and conifers, which have 23% and 25% of species threatened, respectively. The situation with amphibians looks similar, with 32% threatened, but information is more limited, so this may be an underestimate. Cycads have a much higher proportion of threatened species, with 52% globally threatened. In regional assessments, taxonomic groups with the highest proportion of threatened species tended to be those that rely on freshwater habitats (C4.4). Threatened species show continuing declines in conservation status, and species threat rates tend to be highest in the realms with highest species richness (C4.4). (See Figures 3.4 and 3.5.)
Threatened vertebrates are most numerous in the biomes with intermediate levels of habitat conversion. Low-diversity biomes (such as boreal forest and tundra) have low species richness and low threat rates and have experienced little conversion. Very highly converted habitats in the temperate zone had lower richness than tropical biomes, and many species vulnerable to conversion may have gone extinct already. It is in the high-diversity, moderately converted tropical biomes that the greatest number of threatened vertebrates are found (C4.4.3). (See Figure 3.6.)
Among a range of higher taxa, the majority of species are currently in decline. Studies of amphibians globally, African mammals, birds in agricultural lands, British butterflies, Caribbean corals, waterbirds, and fishery species show the majority of species to be declining in range or number. Increasing trends in species can almost always be attributed to management interventions, such as protection in reserves, or to elimination of threats such as overexploitation, or they are species that tend to thrive in human-dominated landscapes (C4.4.1). An aggregate indicator of trends in species populations—the Living Planet Index—uses published data on trends in natural populations of a variety of wild species to identify overall trends in species abundance. Although more balanced sampling would enhance its reliability, the trends are all declining, with the highest rate in freshwater habitats. (See Figure 3.7.)
Genetic diversity has declined globally, particularly among domesticated species (C26.2.1). In cultivated systems, since 1960 there has been a fundamental shift in the pattern of intra-species diversity in farmers’ fields and farming systems as a result of the Green Revolution. Intensification of agricultural systems coupled with specialization by plant breeders and the harmonizing effects of globalization have led to a substantial reduction in the genetic diversity of domesticated plants and animals in agricultural systems. The on-farm losses of genetic diversity of crops have been partially offset by the maintenance of genetic diversity in gene banks. A third of the 6,500 breeds of domesticated animals are threatened with extinction due to their very small population sizes (C.26.2). In addition to cultivated systems, the extinction of species and loss of unique populations that has taken place has resulted in the loss of unique genetic diversity contained in those species and populations. This loss reduces overall fitness and adaptive potential, and it limits the prospects for recovery of species whose populations are reduced to low levels (C4.4).
Globally, the net rate of conversion of some ecosystems has begun to slow, and in some regions ecosystems are returning to more natural states largely due to reductions in the rate of expansion of cultivated land, though in some instances such trends reflect the fact that little habitat remains for further conversion. Generally, opportunities for further expansion of cultivation are diminishing in many regions of the world as the finite proportion of land suitable for intensive agriculture continues to decline (C26.ES). Increased agricultural productivity is also lowering pressures for agricultural expansion. Since 1950, cropland areas in North America, Europe, and China have stabilized, and even decreased in Europe and China (C26.1.1). Cropland areas in the former Soviet Union have decreased since 1960 (C26.1.1). Within temperate and boreal zones, forest cover increased by approximately 3 million hectares per year in the 1990s, although about half of this increase consisted of forest plantations (C21.4.2).
Translating biodiversity loss between different measures is not simple: rates of change in one biodiversity measure may underestimate or overestimate rates of change in another. The scaling of biodiversity between measures is not simple, and this is especially significant in the relationship between habitat area and species richness. Loss of habitat initially leads to less species loss than might be expected, but depending on how much habitat remains, rates of loss of habitat can underestimate rates of loss of species (C2.2.4, C4.5.1).
Biotic homogenization, defined as the process whereby species assemblages become increasingly dominated by a small number of widespread species, represents further losses in biodiversity that are often missed when only considering changes in absolute numbers of species. Human activities have both negative and positive impacts on species. The many species that are declining as a result of human activities tend to