Environmental Engineering Reference
In-Depth Information
functional diversity. Genetic diversity usually refers to the genetic variation
that exists within a species (the gene pool).
Genes are the fundamental unit
of biodiversity and the ultimate source of all variation among all animal
and plant species (Dobzhansky, 1970; Soulé and Wilcox, 1980). Genetic
diversity has been proposed as the basis on which to make conservation
decisions using the evolutionary distinctiveness of taxa when assigning
them priorities for preservation (Vane-Wright et al., 1991; Crozier, 1992;
Solow et al., 1993; Weitzman, 1998). Here, the relative ecological value is
based on how far away species are from one another genetically and an
objective value is assigned to the taxonomic distinctiveness or degree of
'independent evolutionary history' (IEH) that is vested in a species (Vane-
Wright et al., 1991).
Conservation organizations frequently employ descriptions and meas-
ures of ecosystem diversity based on genetic diversity and they tend to
place great emphasis on species and their populations (IUCN, 1988).
Although considerable sums have been allocated towards species preser-
vation, there is frequently a bias towards charismatic species, large birds
or mammals that are very familiar to the public. Conservation groups and
professional conservationists often exploit certain species and ecosystems
to further their own conservation goals. Conservationists have called
the charismatic species that win the hearts of the general public 'l agship
species'. This may be at the expense of less well-known species that may be
critical for the functioning of ecosystems (Metrick and Weitzman, 1994).
Understanding the value of biodiversity to land managers requires a
dif erent perspective that is linked to the functional value of biodiversity.
How then does functional diversity dif er from genetic diversity and if
so, why do these dif erences matter to managers? First, genes are after
all just chemicals that have no value in and of themselves. Instead, genes
have value in what they do - control the structure and function of life -
instead of in what they are. Measures of genetic distance may not capture
the relative values of species such as the complex functional relationships
embodied in ecosystems. Two species might be very similar with respect to
genetic distance but they may perform very dif erent functions within the
ecosystem. One might be a keystone species that is vital to the well-being
of the managed ecosystem whilst the other is 'functionally redundant'.
Species diversity is relevant
to land managers because some species appear
to play a more important functional role than others. An individual who is
evaluating a species in terms of its functional role would be more sensitive
to a change in the ecosystem's productivity than would a person focusing
on biodiversity. A person assessing an ecosystem from an ecosystem func-
tion perspective would be more likely to focus on key species and processes
and might overlook the disappearance of a rare species. There is greater
