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Our Planet Reviewed - Expedition Papua New-guinea :: Rubriques

Our Planet Reviewed - Expedition Papua New-guinea


Our planet reviewed

Mapping biodiversity: the hotspots

At the end of the 1980ies, a revolution took place in the area of the biology of conservation. Its beginning was the question of a researcher, Norman Myers: “In which area of the world does a dollar spent have the biggest effect on slowing down current extinction?” In an attempt to answer this question, he made a synthesis of the existing literature which led to the formulation in 1988 of his theory of hotspots, “the most important contribution to the biology of conservation of the last century” according to Edward O. Wilson, one of the fathers of the concept of biodiversity:diversity of all the forms of living. Schematically, biodiversity is studies at three levels: ecosystems, the species of which these ecosystems consist and finally the characteristic genes of each species.. On the basis of these works, the NGO Conservation International, founded in 1987, defined a number of hotspots. Today there are 34 hotspots which are the object of a widely shared consensus. Among these, the destinations of “La Planète Revisitée” have been chosen. 

For a region to be considered as a hotspot of diversity, two conditions have to be fulfilled:
- the region has to accommodate at least 1,500 species of vascular plants (any plants, except for algae, mosses and lichen), i.e. more than 0.5% of the total number of species of vascular plants : Vegetal characterised by the presence of roots, a stem, leaves and special tissues forming vessels which allow for the circulation of the sap. The name vascular plant thus refers to plants with flowers and seeds as well as to ferns.which are currently known. These plants have been chosen as references since these are the most comprehensively recorded ones amongst living species.
- the region has to have lost more than 70% of its species since the period of time when people started to modify landscapes, i.e. about 8,000 years ago.
However, despite these common criteria, the level of threat weighing on each hotspot may vary considerably. For example, the southern forests of Chile, the least degraded hotspots, still preserve 30% of their initial coverage while no more than 10% of the original surfaces of the ecosystems of the 11 most threatened hotspots are left.
It is these 11 regions where a record number of species of plants and endemic animals whose extinction is imminent and on which the expeditions of “La Planète Revisitée” will focus concentrates.

There, the researchers will establish detailed inventories of the limited geographical areas while concentrating on the small species which are naturally rare and habitually neglected by the organisms of protection and conservation. In fact, although the “Rapid Assessments*” which are used for rapidly mapping hotspots of the planet have proven their effectiveness, the majority of them is based on the “big charismatic fauna” and vascular plants. This approach leaves numerous species which are less “visible” (fungi, insects etc.) aside although this small nation of biodiversity play a fundamental role within the frame of ecosystems.

Hotspots, one vision among others


Although the scientific community globally and enthusiastically appreciates hotspots, these still raise a number of questions. First of all, the lack of reliable data regarding the distribution of species over the planet constitutes an important bias within the evaluation of the zones to be protected. Certainly, the hotspots concentrate 42% of the endemic species of vertebrates and 50% of the endemic vascular plants on 16% of the emerged surfaces but the major part of biodiversity consists of the smaller species which are hardly known. Moreover, the criteria for the selection of hotspots which are very arbitrary are also being discussed: the variations of the vegetal biodiversity cannot be systematically superposed to the variations of the biodiversity of other species. This finding prompted Birdlife International to define “endemic bird areas” which decisively differ from hotspots. In fact, the hotspots are mainly located in tropical forest areas which excludes ecosystems such as swamps which are however important for the biogeochemical cycles. In order to include these “cold spots” in the agendas of conservation, the WWF thus decided to define “ecoregions” on the basis of the criteria of endemism, specific richness and taxonomic rarity on the one hand and of the presence of original ecological and evolution processes on the other hand.
All these points of view which are at a time complementary and divergent are the expression of one single reality: we are terribly lacking knowledge on our environment and only the synergy of all the actors of conservation will allow for a bridging of these gaps.

Marine environment: a particular problem


If the notion of geographic areas has a sense when one considers terrestrial ecosystems, things get complicated as soon as the interest is directed at the marine environment. In fact, the spatial distribution of species is very different, there, and there is actually no notion of endemism as per country or micro-region. Instead, what can be found in the oceans are zones which accommodate a large biodiversity such as South-East Asia and the Coral Triangle as well as the peripheral zones which are mainly less rich in species (even though the latter may sometimes accommodate specimen which are important due to their originality although they are less populated). In other words: if it is possible for terrestrial ecosystems to identify those zones which should be preserved with priority by crossing the criteria “numerous endemic species” + “considerable destruction of habitats”, this framework does not apply to the oceans. However, these cover more than 70% of the planet and accommodate 32 of the known 33 phylums 15 of which are exclusively marine! In the oceans more than in the geographical regions, it is mainly the condition of the various big types of habitats (coral reefs, mangroves...) which will help to measure the vulnerability of marine species.