Geography Reference
In-Depth Information
Figure 15.5
Densities of
larvae of the larch bud moth
(Zeiraphera diniana)
on larch
in Switzerland.
Source:
Baltensweiler1984.
risk diverting resources to those species that are
least likely to survive in the long term. It would
be both less costly and probably more effective if
conservation projects sought to protect viable
populations of more common species within their
native range to prevent them ever reaching
endangered status. It should not be assumed that
rarity is synonymous with vulnerability to
extinction. Many species are naturally rare,
especially at the limits of their range. Rarity is also
scale-dependent; local rarity does not always imply
that an organism is regionally rare.
to draw up species distribution maps and compare
these with maps of existing protected areas. This
procedure has been termed 'gap analysis' (Scott
et
al
. 1993) and is an approach that has been made
considerably more tractable by the development
of sophisticated geographic information systems.
Such an approach makes good sense, because most
species are distributed in a strongly non-random
pattern. Similar biogeographical histories for many
species mean that their distribution patterns
coincide. The effectiveness of protected areas in
protecting species and habitats can be increased
significantly by the selection of diversity hotspots,
where the ranges of large numbers of species
overlap.
Part of the rationale for protecting biodiversity
is the belief that it may contribute to future
evolutionary potential. Giving priority for
conservation to areas that encompass the greatest
possible species diversity may not be the best way
of retaining the greatest capacity for further
evolutionary development (Brooks
et al
. 1992).
Areas that contain a diversity of habitats will often
contain large numbers of species. However, close
juxtaposition of habitats within a restricted area
may mean that they are at marginal ecotones and
no one habitat may be adequately represented.
Areas that have been the focus of evo-lutionary
Selection of protected areas
As attempts to protect endangered species have so
frequently proved inadequate, an alternative
strategy for biodiversity conservation is one that
protects the greatest variety of species and habitats.
There are two distinct problems that face
conservation in its efforts to select areas for
conservation. The first is to ensure that all valuable
facets of diversity are protected. This involves some
form of biodiversity inventory. The second
problem is to make provision for their protection
in perpetuity.
The most logical way to identify which species
and habitats are inadequately protected would be
