K K Vinod
In situ conservation, is the continuation of this
traditional method of informal breeding that distinguishes in situ from
ex situ conservation on farms and in gardens. However, many developed
countries now have legislation protecting plant breeders' rights, which
effectively prevents the continuation of traditional agriculture and therefore in
situ conservation of crop species. This section therefore applies to in
situ conservation of wild species, and of crop species only in those
countries where legislation permits.
Sites for inclusion in a network for in situ conservation
must be chosen to maximize the diversity that can be maintained. This is
similar in principle to choosing sites for collection to maximize diversity
collected.
Sites should cover the entire ecological range of
the species, with a bias towards its centre(s) of diversity and the ecological
extremes of its distribution. There should be a stratified distribution of
sites with several levels of clustering: each site should be large enough to
encompass a cluster of several genetic populations; each site should be part of
a cluster of several nearby sites, close enough for occasional gene flow between
sites as a result of rare long-distance dispersal events; each cluster of sites
should be part of a larger cluster; and so on to encompass the entire range of
the species. Such stratification will serve a dual purpose of: (i) optimizing
gene flow within and between populations; and (ii) encompassing the maximum
possible range of types of diversity. Within the general stratification, sites
and clusters should be chosen to maximize diversity of environments and
therefore of selection pressures within and between sites and clusters. As
always, of course, diversity of selection pressures is taken to include
artificial as well as natural selection, with diversity associated with variation
in local preferences and farmers' concepts of quality and agronomic value.
The shape of sites and clusters also needs
consideration. For example, linear habitats may be useful to
increase connectivity between clusters with minimal increase in areas of the
region set aside for conservation. For rare species, there may be a need to
create new populations at sites with sufficient connectivity to existing
populations to prevent loss of diversity through inbreeding.
Additional measures can be taken to increase
biodiversity within the selected network of conservation sites, essentially by
increasing the diversity of environments and selection pressures within and
between sites.
For crop species, farmers can be actively
encouraged to value the distinctiveness of the traditional farming practices
of the region; and the local customer community can be actively encouraged to
value the distinctiveness of local traditions and their consequent demands on
local farmers. Important traditional farming practices can include factors such
as conscious selection by the farmer for genetic variation within and between
varieties for tolerance to disease, drought, heat, etc. These traditions are
based on utilizing high diversity to provide low-cost, sustainable, low-risk
protection from environmental stresses and hazards. That is, they benefit not
only conservation of biodiversity but also the farm economy.
For wild and some crop species, there can also be
opportunities for increasing diversity by appropriately diverse management.
Emphasis is on diverse management, as many management procedures, especially
mechanized ones, tend to reduce diversity. For example, cutting, liming,
fertilization and control of weeds, pathogens and pests are usually applied
uniformly across entire sites; in so doing they reduce environmental diversity
and therefore the diversity of selection pressures and biodiversity at the
scale of the site. If such procedures are also applied consistently from year
to year, there will also be less temporal variation in selection pressures,
again reducing biodiversity at the scale of the field. In contrast, management
by grazing imposes cutting, trampling and fertilization that is spatially and
temporally variable - to an extent that depends on the grazing behaviour of the
selected herbivore.
Similarly, diversity of management should be
encouraged at larger scales, including landscape and regional. The principal
problem here relates to how to construct and implement a conservation policy.
For example, a management policy may be implemented that maximizes biodiversity
within a field; but if that same policy is applied to all sites, the same range
of biodiversity will be promoted at all sites, reducing biodiversity at the
larger landscape and regional scales. If the policy is to be centrally
established and imposed, it may be economically impossible to incorporate the
larger-scale variation in management necessary to maximize biodiversity at
landscape and regional levels. A decentralized system is likely to be
preferable, especially to incorporate regional variations in traditions.
We have seen that biodiversity is a scale-dependent
phenomenon and that for its efficient conservation we need to include all
scales from a few square centimetres to thousands of square kilometres. We have
also shown that the distribution of genetic diversity of any species depends
on its life cycle and consequent evolutionary characteristics. Efficient
conservation depends on having a good knowledge of population structure and the
life cycle characteristics that determine this - dispersal profiles, breeding
system and longevity. The same principles apply not only to wild species but
also to crop species, the major difference being that crop species have
dispersal profiles determined largely by the farmer and market, and are
subject to artificial selection by the farmer as well as natural selection.
References:
Forman, R.T.T. (1995) Land Mosaics: the Ecology of Landscapes and Regions.Cambridge University Press, Cambridge.
