Migration

It is a two way periodic or seasonal dispersal of population. These types of movements are seen in mammals, birds, fishes and some insects particularly.

• The fishes which migrate from freshwater to the ocean for egg laying are called as catadromous and those which migrate from ocean to freshwater are called as anadromous.
• Birds are the best examples of migratory movements. Birds usually breed in coldest part of their range so in the Northern Hemisphere, birds move towards north in spring and to south in autumn.
• Migration can be emigration (The outward movement of organisms) and immigration (the inward movement of organisms).

STATUS OF BIODIVERSITY IN INDIA:

India has a rich and varied heritage of biodiversity, encompassing a wide spectrum of habitats, from tropical rainforests to alpine vegetation and from semi-arid vegetation to coastal wetlands. India figured with two hotspots - the western ghats and the eastern himalayas - out of 25 biodiversity hotspots identified by Myers (1988). In addition, India has 26 recognized endemic centres that are home to nearly one third of all the flowering plants identified and described to date.
Of the 1.7 million of the world’s described biota, India contributes 7.3% of the global fauna.

Among flowering plants, India accounts for 7% of the 250,000 flowering plants so far described in the world. India is one of the 12 centres of origin of cultivated plants. There are 167 cultivated species and 273 wild relatives of crop plants. The endemism of Indian biodiversity is high.

About 33% of the country's recorded flora (49,219 plant species) are endemic to the country and are concentrated mainly in north-east India, the western ghats, north-west himalayas and the Andaman and Nicobar islands. In animals, the endemism among mammals and birds is relatively low (6 to 9%). However, the amphibians and reptiles are, respectively, nearly 62 and 50% endemic to India, and the majority of them are found in the western ghats. In India, as in many tropical regions of the world, deforestation and forest degradation continue due to various factors such as extension of cultivation, grazing, extraction of forest products, hydroelectric projects and commercial plantations. Because of these activities, for example, in the western ghats, nearly 40% of the natural vegetation has disappeared during the last 8 decades. In north-east, central and eastern India, shifting cultivation is a major reason for forest degradation and loss. According to one estimate, about 6.4 million hectares are affected by shifting cultivation.

Deforestation leads to several changes in the landscape. The degradation and fragmentation of forests, which generally precede deforestation, considerably affect the biodiversity. Several species with narrow distribution patterns become extinct and several rare and endemic species become endangered or threatened. According to the IUCN, 2000 Red List Data, India contains nearly 3% of the world's total number of threatened species. These include 86 species of mammals, 70 birds, 25 reptiles and 3 amphibians. Among plants, 19 are extinct, 44 critically endangered, 113 endangered and 87 vulnerable.