This article provides study notes on global biodiversity.
1.4 million Species of various life-forms have been enlisted so far.
These include 300,000 species of vascular plants; 40,000 species of vertebrates; 800,000 species of insects; 360,000 species of microorganisms (Table 1).
However, these estimates are increasing all the time.
A conservative estimate of the total figure would be 14 million. According to some recent estimates, the number of insects alone may be as high as 10 million. This means that only 13% of the total biodiversity on earth has been described.
(i) Total Number of Species of Plants and Microbes:
It is evident from Table 2 that about 4,000 different viruses are known to date. A conservative estimate of the total number of viruses is 400,000. Thus, we know only 1% of the existing viruses.
About 5,300 species of bacteria (including 1,700 species of cyanobacteria) have been recorded so far. According to an estimate total number of bacterial species on the Earth is around 400,000.
Fungi and Lichens:
More than 70,000 species of fungi (including about 17,000 species of lichens) are known to us. The conservative figure for existing fungal species on the Earth is about 1.5 million.
So far 40,000 species have been described and another 300,000 species are believed to exist on the Earth. Algae yet to be described are likely to come from open ocean as well as from polar regions.
So far 19,000 species of bryophytes are known, of which about 10,000 species are mosses, 8,000 species liverworts and 800 species of hornworts. The number of bryophyte species is likely to increase to about 30,000, if more areas are explored.
The Pteridophytes are vascular land plants and together with Gymnosperms and Angiosperms dominate terrestrial communities of the world. There are about 15,000 species of Pteridophytes known to us.
Most species of Gymnosperms are trees, although a few species are shrubs. There are about 750 species of this group.
The angiosperms or flowering plants constitute the most diverse group of vascular plants. There are about 300,000 species described so far. This group is very recent (35 million years) to evolve in the geological history but have become the most dominant of all plants because of their great evolutionary capabilities. Plant families vary considerably in the number of their constituent species, e.g. the Orchidaceae contains 25,000-35,000 species and the Leguminosae about 15,000 species. A total of 31 families comprise 62% of the known angiosperm species; 36 families like Adoxaceae are mono-specific.
(ii) Total Number of Species of Animals:
Invertebrates as a whole includes little over one million species, distributed among nine major phyla. These include 800,000 species of insects, 5,000 species of sponges, 38,000 species of molluscs and 9,000 species of crustaceans (Table 1 and 2). The number of species of vertebrates in the world is about 40,000. These include 2,400 species of amphibians, 6,100 species of fish, 6,300 species of reptiles, 9,035 species of birds and 4,230 species of mammals.
(iii) The Mega Diversity Countries of the World:
Warm and humid regions in between the Tropics of Cancer and Capricorn are provided with a rich and diverse plant, animal and microbial life. In this wide belt around the globe occurs more than half of the total number of species present on our planet. Countries which happen to lie in this zone are referred to as Mega diversity countries, as they possess a wide variety of plants and animal species.
These countries are Brazil, Columbia, Mexico, Indonesia, Peru, Malaysia, Ecuador, India, China, Zaire, Madagascar and Australia. Table 3 provides the approximate number of flowering plant species recorded in the mega diversity countries on the Earth.
(iv) Endemism and ‘Hot-Spots’ of Biological Diversity:
Endemic species can be defined as those species which are confined only to a particular locality. There are two important categories of endemic species—Palaeoendemics and Neoendemics. Palaeoendemics are phylogenetically distinct taxa which arose in Tertiary and bound to islands or environmentally isolated situations. Neoendemics are those which have arisen relatively recently. Endemism represents a unique step in the process of evolution which could be perpetuated and sustained only in the locality concerned depending on the environmental quality.
It is the environment which is instrumental in the operation of the process of natural selection. This makes the habitats in which endemic species thrive very important. The importance of the habitat is further highlighted by the fact that in most of the cases such localities possess a number of endemic species distributed in several taxonomic categories. There should always be a sustained effort to conserve the endemic species and their habitat.
Areas where high levels of species richness, threat and endemism coincide are termed as hotspots. The concept of biodiversity hotspots was originated by Dr. Norman Myers (1988 & 1990). He first identified ten tropical forest ‘hotspots’ characterized both by high level of plant endemism and by serious level of habitat loss.
In 1990 Myers added further eight ‘hotspots’, including four Mediterranean-type ecosystems. In 1996 Conservation International (CI) decided to undertake a reassessment of the hotspots concept, including an examination of whether some key areas had been overlooked. Three years later (1999) an extensive global review was undertaken for the designation of biodiversity hotspots and 25 biodiversity hotspots were identified (Myers et al. 2000).
To be identified as a hotspot, a region must meet two strict criteria: (i) it must contain at least 1,500 species of vascular plants (>0.5 % of the world’s total) as endemics, and (ii) it has to have lost at least 70% of its original habitat. These areas (25 hotspots) contain 44% of the world’s plants as endemics and 35% of the terrestrial land vertebrates in an area of 1.4% of Earth’s land surface.
Recently, 34 biodiversity hotspots have been identified covering only 2.3% of the Earth’s land surface. Over 50% of the world’s plant species and 42% of all terrestrial vertebrate species are endemic to these 34 designated hotspots. The 34 hotspots, distributed in different regions of the world are listed below:
North and Central America:
1. California Floristic Province,
2. Caribbean Islands,
3. Madrean Pine-Oak Woodlands,
5. Atlantic Forest,
7. Chilean Winter Rainfall-Valdivian forests,
9. Tropica Andes.
Europe and Central Asia:
12. Mediterranean Basin,
13. Mountains of Central
14. Cape Floristic Region,
15. Coastal Forests of Eastern Africa,
16. Eastern Afromontane,
17. Guinean Forests of West Africa,
18. Horn of Africa,
19. Madagascar and the Indian Ocean Islands,
21. Succulent Karoo.
22. East Melanesian Islands,
23. The Himalaya,
26. Mountains of Southwest China,
27. New Caledonia,
28. New Zealand,
31. Southwest Australia,
34. Western Ghats and Sri Lanka.