2.2 Extent and Determinants of Genetic Extinction
17
According to the Convention on Trade in Endangered Species of Wild Fauna and
Flora (CITES), only those species may be cited as extinct which have not been
recorded for at least 50 years (CITES, 1993). Consequently, current extinction is
seldom documented yet.
Fig. 2.2. Impact of various activities on present biodiversity
deterministic processes:
human induced:
habitat modification
habitat fragmentation
habitat destruction
import of new
species
stochastic processes:
survival of the fittesV
import of new species by invaders
mutation
adaptation
natural catastrophes
(fire, drought, flood ... )
Because of the difficulties described, estimates for present and future
extinction rates for plants are not based on reported and documented extinction,
but rather on models. These incorporate extrapolations from estimated habitat
destruction, combined with bio-geographic assumptions derived by relating the
numbers of species to the area of habitat. Another major difficulty in recording
the decline of biodiversity is the determination of a causal link between human
activities and extinction of species, which is necessary for the estimates. (Jenkins,
1992).
For the most part, the studies have been based on the estimated species richness
of tropical forests combined with their known and estimated deforestation rates.
Estimates of the extinction rate of plant species range between 1 % and 11% per
decade depending on the assumed rate of deforestation and the relation between
the number of species and the existing area (see Table 2.3). The different results
depend to a large extent on the prospected development of the available area,
which determines the relation between the number of species and the existing
area.
Some major shortcomings in this approach must be considered when citing the
estimated values. These estimates include plant as well as animal species. Hence,
17
According to the Convention on Trade in Endangered Species of Wild Fauna and
Flora (CITES), only those species may be cited as extinct which have not been
recorded for at least 50 years (CITES, 1993). Consequently, current extinction is
seldom documented yet.
Fig. 2.2. Impact of various activities on present biodiversity
deterministic processes:
human induced:
habitat modification
habitat fragmentation
habitat destruction
import of new
species
stochastic processes:
survival of the fittesV
import of new species by invaders
mutation
adaptation
natural catastrophes
(fire, drought, flood ... )
Because of the difficulties described, estimates for present and future
extinction rates for plants are not based on reported and documented extinction,
but rather on models. These incorporate extrapolations from estimated habitat
destruction, combined with bio-geographic assumptions derived by relating the
numbers of species to the area of habitat. Another major difficulty in recording
the decline of biodiversity is the determination of a causal link between human
activities and extinction of species, which is necessary for the estimates. (Jenkins,
1992).
For the most part, the studies have been based on the estimated species richness
of tropical forests combined with their known and estimated deforestation rates.
Estimates of the extinction rate of plant species range between 1 % and 11% per
decade depending on the assumed rate of deforestation and the relation between
the number of species and the existing area (see Table 2.3). The different results
depend to a large extent on the prospected development of the available area,
which determines the relation between the number of species and the existing
area.
Some major shortcomings in this approach must be considered when citing the
estimated values. These estimates include plant as well as animal species. Hence,