1: What is it, where is it, and why is it important?

o 1.1 What is biodiversity?

o 1.2 Where is biodiversity?
o 1.2.1 Spatial Patterns of Biodiversity
o 1.2.2 Temporal Patterns of Biodiversity
o 1.3 What is the link between biodiversity and ecosystem services?
o 1.3.1 Supporting Services
o 1.3.2 Regulating Services

1.1 What is biodiversity?

The source document for this Digest states:
o 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.
o Biodiversity forms the foundation of the vast array of ecosystem services that critically
contribute to human well-being.
o Biodiversity is important in human-managed as well as natural ecosystems.
o Decisions humans make that influence biodiversity affect the well-being of themselves
and others.
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) 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.
BOX 1.1

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.
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.
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.
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)

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.)

Importance of Quantity and

Level Importance of Variability
Distribution

adaptive variability for production and

Genes resilience to environmental change, local resistance and resilience
pathogens, and so on

different populations retain local local provisioning and regulating

Populations
adaptation services, food, fresh water

community and ecosystem interactions

the ultimate reservoir of adaptive
Species are enabled through the co-occurrence
variability, representing option values
of species

the quantity and quality of service

different ecosystems deliver a
Ecosystems delivery depend on distribution and
diversity of roles
location

Source: Millennium Ecosystem Assessment

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 (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 CO 2 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. (See Box
1.4)."
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.
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:
• Provide information about changes in important processes
• Be sensitive enough to detect important changes but not so sensitive that signals
are masked by natural variability
• Be able to detect changes at the appropriate temporal and spatial scale without
being overwhelmed by variability
• Be based on well-understood and generally accepted conceptual models of the
system to which it is applied
• Be based on reliable data that are available to assess trends and are collected in a
relatively straightforward process
• Be based on data for which monitoring systems are in place
• Be easily understood by policy-makers