Our Environment - Mining and the Environment: From Ore to Metal - page 321

Although the concept
of naturalness is easy to
understand, and its relevance
to environmental assessment
process and conservation is
intuitive, it is often more diffi cult
to defi ne and to quantify.

contrary, the island of Papua is considered as the place on Earth with the highest concen-
tration of distinct tribes and languages.
The nature quality concept is usually closely related to naturalness. Although the con-
cept of naturalness is easy to understand, and its relevance to environmental assessment
process and conservation is intuitive, it is often more difficult to define and to quantify.

Diversity
The use of the term 'diversity' has increased tremendously over the last years, especially
since the Rio Earth Summit, which made politicians and their audiences aware of the
term. Diversity however is an older concept in ecology, and it had been used as a value
criterion as well as in ecological studies long before the Rio summit. It has been referred to
as community, habitat, or species diversity by Margules and Usher (1981). Diversity may
appear to be a straightforward and easily measured concept. Most people have an intui-
tive idea of what is meant by diversity, but nevertheless there is no consensus of how it
should be defined and measured. Perhaps the reason is that diversity has two compo-
nents. Diversity may refer to the number of different species, the species richness, but also
to their relative abundance (Magurran 1988). Whittaker (1972) introduced the concept of
alpha, beta, and gamma-diversity, thereby relating diversity to geographical scale. Alpha-
diversity is the number of species found in a small homogeneous area, while beta-diver-
sity is the difference in species composition between different sites (or along gradients),
the so-called species turnover. Gamma diversity is the total diversity in the area. These
concepts are obviously scale dependent. Noss (1990) offered a hierarchical approach in
which structural, compositional, and functional diversity is recognized at multiple levels
of organization: genes, species, community, and landscapes. His concept has many features
in common with the definition of biodiversity from the UN Convention of Biological
Diversity. It was suggested as a guideline for the monitoring of biodiversity. By choosing
good indicators, the topic of the next section, the approach may also offer some opportuni-
ties for site assessment.

Rarity
As with diversity defining rarity as a value criterion is not easy. Both man-induced and
natural factors may contribute to the rarity of a species. Rarity is often assumed to be
related to vulnerability - the rarer a species, the more vulnerable it will be, and the more
likely to become extinct. Therefore information on rarity is important for classification
of species in terms of their conservation status. Rabinowitz et al. (1986) introduced a
clarifying concept of rarity by partitioning the species distribution and abundance into
three levels. The species are subdivided according to (1) geographic range (extensive ver-
sus restricted), (2) habitat tolerance (broad versus narrow), and (3) local population (large
versus small) as shown in Figure 7.5 . By combining these three categories, one class of
common species and seven classes of rarity emerge. Species with a wide geographical dis-
tribution, wide habitat demands and large population sizes, are common species not par-
ticularly vulnerable. Species with a small population size and/or narrow habitat demands
are more or less vulnerable depending on the intensity and extent of disturbance. Species
both with small population size, small geographical distribution, and narrow habitat
demands are on the other hand very vulnerable to disturbances. A somewhat similar
approach is discussed by Smith and Theberge (1986), with emphasis on geographic and
demographic criteria. They discern five types of rarity. Widespread rare species are spe-
cies with a wide geographic distribution, but they are scarce wherever they occur. Tigers
are an example of widespread rare species. Endemic species have a restricted geographic
range, while disjunct species have populations separated from the main range of the

Rarity is often assumed to be
related to vulnerability - the rarer
a species, the more vulnerable
it will be, and the more likely to
become extinct.