Habitat loss and degradation affects 89% threatened birds, 83 % mammals and 91% threatened plants assessed (IUCN, 2000). Habitat loss is due to agricultural activities, mining, fishing, logging, harvesting and development.
Habitat loss and fragmentation leads to formation of isolated, small, scattered populations which are vulnerable to inbreeding depression, high infant mortality and susceptible to environmental stochasticity and consequently possible extinction. Hunting, collecting, fisheries and trade are major threat to birds (37%), mammals (34%), plants (8%), reptiles and marine fishes. Poaching is one primary reason for decline in number of species like tiger. Poaching pressures are unevenly distributed. Alien invasive species affects 350 (30% of all threatened) birds and 361 (15% of all threatened) plant species. Islands are particularly susceptible to such invasions. Underlying causes of biodiversity loss are poverty, macroeconomic policies, international trades, policy failure, poor environmental law/weak enforcement, unsustainable development project and lack of local control over resources (Wood et al., 2000).
Population’s pressures and concomitant increase in collections of fuel wood and fodder, grazing in forests by local communities to take their toll on forests and its biodiversity (IUCN, 2000). Threat to biodiversity due to invasive alien species is considered second only to that of habitat destruction. About 40% Indian floras are alien, of which 25% are invasive. Parthenium hysterophorus, an exotic species of Tropical America has naturalised in most parts of India. This is a noxious weed because of its prolific seed production, fast spreading ability, allelopathic effects on other plants and health hazard to human and other animal. Mikania micrantha, a perennial fast growing weed of Neotropical region, is a major menace in natural forests, plantations, agricultural systems in northeast and southwest India. Lantana camara, one of ten worst weeds of world and a native of subtropical America, is now found all over the Indian Subcontinent.
Ageratum conyzoides, a native to South America is found in several parts of southern Asia including India. In marine environment, ships are major sources for transfer of invasive species. Eichhornia crassipes introduced from Brazil is a most nuisance aquatic hydrophyte as it causes hindrance to navigation. Many freshwater and marine algae including Microcystis, Caulerpa, Chulophora cause extensive damage to ecosystem and affect aquatic biodiversity adversely. However, little information exists regarding invasive fauna and microbes in India. Species of parasites dodders (Cuscuta spp.) are becoming a serious problem in agroecosystems of south India and are being seen increasingly on many plants including rice, throughout the country (Raghubanshi et al., 2005).
Effective management of invasive species requires knowledge about their ecology, morphology, phenology, reproductive biology, and physiology. Taking into consideration the major changes occurred in the IUCN Red List Criteria and IUCN guidelines in the year 2000, it is felt absolutely necessary to revise the Red Data Book of 1994 published by ZSI. It is also felt necessary to take into consideration other conservation measures like CITES and Indian Wildlife (Prelection) Act in addition to IUCN. When a list of mammal species alone was prepared with higher conservation status as per the amendments made at national and international levels, it has been observed that the figure was 150. That means almost 50% of Indian mammal species were under some or other criteria of higher conservation status.
The list included many of the less-charismatic and unknown species which are badly in need of protection for their survival.