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| Biodiversity loss
and its causes |
Spéciations
ed extinctions
Speciation and extinction constitute natural phenomena that
have been taking place for ages, before arriving at the
actual life forms. Although the massive extinctions of the
past, 40.000 years ago when the first Homo sapiens appeared,
took place gently and slowly, so that new life forms have
been able to adapt to a continuously changing world, species
disappearance was too rapid to allow the process of natural
evolution. Rapid extinctions, such as those taking place
today, cannot be balanced by speciation, a process that
normally anticipates very long time periods, of 2.000-100.000
generations (Dallai R., 2005).
Global biodiversity, therefore, has been progressively
reduced since man appeared. This phenomenon has started
around 10.000 years ago, as man began to develop his agrarian
abilities since the Industrial Revolution, the man-induced
biodiversity loss has become more and more accentuated.
From cutting down trees with stone tools to demolishing
mountains in order to get access to the resources of the
planet, man has redesigned the landscape in a definitive
and drastic way. Old harvesting practices have been replaced
by intensive technologies that have often caused, despite
the obvious advantages, the decline of local economies,
due to the insane over-exploitation of natural resources.
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Fishing
with sonar instruments and using more extensive
fishing nets have exhausted the marine resources
of areas where fishing was the indigenous population’s
livelihood (© 2005 Martino Coppola di Canzano).
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The phenomenon of geneti
erosion and the subsequent biodiversity loss has intensified
for various reasons, among which :
- habitats destruction (e.g. : draining and deforestation)
;
- intensive agriculture ;
- landscape fragmentation ;
- overgrazing ;
- colonization by invasive species.
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The deforestation
of tropical forests, the planet «lungs »
and precious biodiversity reservoirs which are
disappearing in a rate of 30 hectares per minute
; the exploitation of large areas and the use
of fertilizers and phytosanitary products ; roads,
railways, tracks that cross over non- urbanised
areas and create fragmented mosaics of green areas
where every isolated unit is not sufficiently
large to accept functional biological communities
; exhaust gases that cause an increase in the
concentration of anhydrous carbon in the air,
climate warming and altered life conditions for
plants and animals ; overgrazing of natural vegetation
by ruminants which restrict the regeneration of
the vegetal cover; the introduction of invasive
species ( e.g. Caulerpa taxifolia) that displace
indigenous species ; all these cause a rapid increase
in the rate of extinction of several species (©
2005 Martino Coppola di Canzano e Gael Farano).
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According to a report from WWF, the world
Organisation for species conservation, more than 30% of
the natural heritage has been destroyed within the last
30 years. Ecosystems have been fragmented or eliminated
and the species will go extinct with a rate of 50-100
times higher than the natural rhythm. If this trend is
not reversed, scientists foresee that within the next
decades, 60% of the living species will be lost; this
would be a real massive extinction, the sixth since the
birth of the Planet.
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Each
species that disappears is lost forever –
the species Nesiota elliptica could be considered
as the symbol of species that are definitively
extinct. The last individual of this tree died
in November 2003 and there is no collection, local
nor international, that conserves germplasm (plants,
seeds, tissues) of this species; it has to be
considered as irremediably extinct. (©
Rebbecca Cairns-Wicks) |
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