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Species
New species may be established in several ways. The most common method is geographical speciation (formation of new biological species), the process by which populations that are isolated diverge through evolution by being subjected to different environmental conditions. Biodiversity is most commonly used and measured by species diversity. There are two major reasons for this: species are still the most easily identifiable collective unit of biological organization and the loss of species seems the most irreversible and final of all forms of diversity. Species diversity can be expressed in terms of richness, that is the number of species in an area – for example you can count the number of plant species in your garden which will give you the species richness of your garden. Thus for example if you have one neem tree and one mango tree in your garden the tree species richness of your garden will be two. Ecologists have come up with various diversity indices, which focus not only on the number of species present but also on the number of individuals of a particular species. Thus for example if you have two neem trees in your garden, this value will be reflected in the diversity index. Diversity indices are of more value to ecologists, since they give an idea of the composition of the communities existing in an area, and help identify species that dominate the community in terms of their abundance, biomass or cover. Let’s take the example of your garden again and make a hypothetical (imaginary) case – say of a total of ten trees in your garden there are 8 neem trees, 1 mango and 1 jamun. What conclusion can you draw from this simple observation? Remember that nature is all about observation and trying to find explanations for whatever exists around you. So 8 neem trees and two other fruit tree species suggest that neem trees are dominant in your garden since they are the most abundant. In this same way ecologists also try to deduce meaning from nature -–trying to find out which species are dominant – they can be dominant in terms of numbers as in your garden (abundance) or biomass (weight) or cover. So nature has dominating species too! Species diversity is not uniform through out the world, some areas are very species rich while others are species poor. Again while one area may have hundreds of plant species another may have an incredible insect diversity. A striking pattern is the increase in diversity from the poles to the equator, thus while the tropical areas team with life, temperate areas which are closer to the poles have fewer kinds of plants and animals, while the polar regions are stark and barren. Tropical rainforests are amazingly diverse, a single hectare may contain 40 to 100 different kinds of trees. Imagine if such diversity existed in your garden you would have to learn the names of many trees since it would be unlikely for you to find two species of the same type. In contrast in a coniferous or a deciduous forest in the temperate zones only about 10 to 30 species can be found. Latitudinal variations are not the only emerging patterns. Diversity is also closely linked to altitude or elevation. The plains of India have a varied species of plants but as you go higher up the Himalayas the number of species decreases. Diversity also decreases with the decrease in the moisture content in the atmosphere, the desert area would have the least number of species. Other than these natural factors there are many reasons for the decrease in species found around the world. A large number of flora and fauna species are in danger of becoming extinct mainly due to the expansion of human activities – the rising population, deforestation, illegal trade in wild life, encroachment into the forest areas, etc. Some of the animals that are endangered are the gaur, wild yak, nilgiri tahr, clouded leopard, tiger, the Indian rhinoceros, pygmy hog, Asiatic lion and many others. The pygmy hog was once found in the Himalayan foothill belt in southern Nepal, northern Bangladesh, Sikkim, Bhutan and adjacent parts of northeastern India. It was considered extinct in the 1960s but was rediscovered in 1971 in northwestern parts of Assam and as its population is still very small it is put in the endangered category. It inhabits the tall grass savanna living in groups of 5 to 20 and feeds mainly on roots, tubers, insects and small mammals. The Asiatic lion was once widely found from northern Greece through Syria, Iraq, Iran to central India. But today the last remaining population is found only in the Gir Forest Sanctuary in Gujarat where it survived due to the patronage of the Nawab of Junagadh. They are now protected under the government of India laws. The world has to wake up to this problem and some action has to be taken for their protection. There are certain species that are endemic to a region that is, they are found in only a particular area and are very special to that area. They have evolved to adapt to that area only and if their habitat is destroyed (e.g. by deforestation) they can easily become extinct. Some plants and shrubs are endemic to only a particular type of forest, such as some found in the evergreen forest will not be found in any other type of forest area. Take the Western Ghats as an example – animals endemic to this area include the Rusty Spotted cat, nilgiri marten, the lion tailed macaque, and the nilgiri languar.
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Species is a group or class of animals and plants
having certain common and permanent characteristics that clearly distinguish it from other
groups or species (Concise Oxford Dictionary). They are populations in which gene flow
occurs under natural conditions. By definition, members of one species do not breed with
those of other species. Unfortunately, this definition does not work in species where
hybridization, self fertilization, or parthenogenesis (reproduction of offspring without
fertilization by sexual union) occurs. 