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Transcript
Module IV – Threats to biodiversity (5 hrs) Types of threats Habitat loss, man- wildlife conflict (with case studies) Invasive species Pollution Over exploitation and human population Climate change THREATS TO BIODIVERSITY Important factors leading to extinction of species and consequent loss of biodiversity are: habitat loss and fragmentation, introduction of non-native species, overexploitation, soil, water and atmospheric pollution, and intensive agriculture and forestry. Habitat loss Habitat loss in the terrestrial domain has been caused largely by the expansion of agriculture: more than 30 per cent of land has been converted for agricultural production. Largescale commercial agriculture has adversely affected biodiversity, particularly agro-biodiversity. Moreover, the growing demand for biofuels has taken a toll, with expanses of forests and natural lands in South East Asia being converted into mono-crop plantations. Direct habitat loss is a major threat to coastal ecosystems through aquaculture. Wetlands in particular have faced a 50 per cent loss in the 20th century. Freshwater ecosystems are severely affected by fragmentation. Benthic habitats have been degraded as a consequence of bottom trawling and other destructive fishing methods Invasive alien species Invasive alien species threaten native biodiversity and are spreading through both deliberate and unintentional introductions as a consequence of increasing levels of global travel and trade. Poorly planned economic introductions, air transport, hull-fouling and ballast water from ships, as well as trade in pets, garden plants and aquarium species, are significant pathways for the dispersal of invasive species. Invasive alien species affect native species principally through predation, competition and habitat modification. They are found in nearly all countries and habitats, including marine ecosystems – for example Pollution 1 Pollutants such as pesticide and fertilizer effluents from agriculture and forestry, industry including mining and oil or gas extraction, sewage plants, run-off from urban and suburban areas, and oil spills, harm biodiversity directly through mortality and reduced reproductive success, and also indirectly through habitat degradation. Inland wetlands and coastal marine habitats face a major threat from waterborne pollutants. Meanwhile, atmospheric pollution in terrestrial systems, particularly the deposition of eutrophying and acidifying compounds such as nitrogen and sulphur is also important. Rates of nitrogen deposition increased sharply after 1940 but have levelled out since 1990, probably owing to an overall decrease in biomass burning, though there is regional variation. Nevertheless, nitrogen deposition continues to be a significant threat to biodiversity, especially for species that have adapted to low-nitrogen habitats Overexploitation Overexploitation of wild species to meet consumer demand threatens biodiversity, with unregulated overconsumption contributing to declines in terrestrial, marine and freshwater ecosystems. In terrestrial systems, major exploited groups include plants for timber, food and medicine; mammals for wild meat and recreational hunting; birds for food and the pet trade; and amphibians for traditional medicine and food The threat to vertebrates from overexploitation is particularly severe, driven, in particular, by demand for wildlife and wildlife products from East Asia In the marine realm, capture fisheries more than quadrupled their catch from the early 1950s to the mid-1990s. Since then, catches have stabilized or diminished, despite increased fishing effort The proportion of marine fish stocks that are overexploited, depleted or recovering from depletion rose from 10 per cent in 1974 to 32 per cent in 2008. Of the 133 local, regional and global extinctions of marine species documented worldwide over the last 200 years, 55 per cent were caused by overexploitation, while the remainder was driven by habitat loss and other threats. The use of destructive fishing practices further amplifies the impacts of unsustainable fishing on marine biodiversity and habitats. Climate change 2 Climate change is an increasingly important threat to species and natural habitats. There is widespread evidence that changes in phenology, including the timing of reproduction and migration, physiology, behaviour, morphology, population density and distributions of many different types of species are driven by climate change. 1. In the Arctic, tundra habitats are shrinking owing to tree-line advance 2. In the marine realm, climate change is causing widespread die-off of coral reefs through rising temperatures and ocean acidification. 3. The Arctic ice cap is also shrinking rapidly, with likely impacts on ice-dependent species 4. For many wetlands, changes in rainfall and evaporation are expected to have major impacts on water regimes, affecting both migratory and residential species. 5. Climate change will also act synergistically with other threats, such as the spread of diseases and invasive alien species. The ecological footprint The ecological footprint is a resource accounting tool that measures how much biologically productive land and sea area – crop and grazing land, forests, fishing grounds and built-up land – is demanded by a given population or activity, and compares this to how much land and sea is available. It has become an increasingly popular headline indicator of broad human pressures on the environment. Ecological footprint analysis shows that the global demand for biologically productive areas has approximately doubled since the 1960s (WWF 2010). In 2007, global society demanded more than 1.5 planets’ worth of productive biological capacity, a deficit that can only be met through the depletion of stocks of renewable resources or the accumulation of waste product, most importantly carbon dioxide (CO2) in the atmosphere. Genetically modified organism (GMO) A genetically modified organism (GMO) is defined by the Cartagena Protocol on Biosafety as any living organism that possesses a novel combination of genetic material obtained through the use of modern biotechnology (CBD 2000); generally by the transfer of genetic material from one species to another. The vast proportion of GM crops has been modified to be tolerant of broad-spectrum herbicides to allow more efficient weed control and/or to express a 3 toxin (Bt) that acts against the caterpillars of butterflies and moths that live and feed inside the crop plants. Genetic modification (GM) remains controversial, both a potential threat and an opportunity for biodiversity conservation, depending on the context. The technology is widely used in pharmaceuticals and crop production, but many consider it an unwarranted risk to the environment and human health. Environmental risks from GMOs 1. Loss of genetic diversity of agricultural species and their wild relatives through gene flow, although this also occurs with non-GM crops. 2. Another concern is the effects on organisms that are not the target of the GM trait, although Bt crops have few toxic effects on non-target species as the Bt toxins produced are highly specific and only expressed in the plant itself. 3. GM crops tolerant of broad-spectrum herbicides such as glyphosate often result in fewer weeds than conventional crops, and therefore make less food available to farmland birds. 4. In addition, species are evolving resistance to both glyphosate and Bt. Habitat Loss and Fragmentation The destruction of habitats is the primary reason for the loss of biodiversity. When people cut down trees, fill a wetland, plough grassland or burn a forest, the natural habitat of a species is changed or destroyed. These changes can kill or force out many plants, animals, and microorganisms, as well as disrupt complex interactions among the species. A forest patch surrounded by croplands, orchards, plantations, or urban areas is an example of fragmented habitats. With the fragmentation of a large forest tract, species occupying deeper parts of forests are the first to disappear. Overexploitation of a particular species reduces the size of its population to an extent that it becomes vulnerable to extinction. Disturbance and Pollution Communities are affected by natural disturbances, such as fire, tree fall, and defoliation by insects. Man-made disturbances differ from natural disturbances in intensity, rate and spatial extent. For example, man by using fire more frequently may change species richness of a 4 community. Then, some human impacts are new, never before faced by biota, e.g. the vast number of synthetic compounds, massive releases of radiation or spillover of oil in sea. These impacts lead to a change in the habitat quality. Pollution may reduce and eliminate populations of sensitive species. For example, pesticide linked decline of fish-eating birds and falcons. Lead poisoning is another major cause of mortality of many species, such as ducks, swans and cranes, as they ingest the spent shotgun pellets that fall into lakes and marshes. Eutrophication (nutrient enrichment) of water bodies drastically reduces species diversity. Introduction of Exotic Species New species entering a geographical region are called exotic or alien species. Introduction of such invasive species may cause disappearance of native species through changed biotic interactions. Invasive species are considered second only to habitat destruction as a major cause of extinction of species. Exotic species are having largeimpact especially in island ecosystems, which harbour much of the world’s threatened biodiversity. A few examples are: (1) Nile perch, an exotic predatory fish introduced into Lake Victoria (South Africa) threatens the entire ecosystem of the lake by eliminating several native species of the small Cichlid fish species that were endemic to this freshwater aquatic system. Water hyacinth clogs rivers and lakes and threatens the survival of many aquatic species in lakes and river flood plains in several tropical countries including India. Lantana camara has invaded many forest lands in different parts of India, and strongly competes with the native species. Extinction of Species Extinction is a natural process. Species have disappeared and new ones have evolved to take their place over the long geological history of the earth. It is useful to distinguish three types of extinction processes. Natural extinction: With the change in environmental conditions, some species disappear and others, which are more adapted to changed conditions, take their place. This loss of species which occurred in the geological past at a very slow rate is called natural or background extinction. Mass extinction: There have been several periods in the earth’s geological history when large number of species became extinct because of catastrophes. Mass extinctions occurred in millions 5 of years. Anthropogenic extinction: An increasing number of species is disappearing from the face of the earth due to human activities. This man-made mass extinction represents a very severe depletion of biodiversity, particularly because it is occurring within a short period of time. The World Conservation Monitoring Centre has recorded that 533 animal (mostly vertebrates) and 384 plant species (mostly flowering plants) have become extinct since the year 1600. More species have gone extinct from the islands than from the mainland or the oceans. The current rate of extinction is 1000 to 10000 times higher than the background rate of extinction. Some interesting observations about the current loss of species are: (1) From ten high-diversity localities in tropical forests covering 300,000 km 2 , some 17,000 endemic plant species and 350,000 endemic animal species could be lost in near future. The tropical forests alone are losing roughly 14000-40000 species per year (or 2-5 species per hour). The earth may lose up to 50% of the species by the end of the 21 current rate of loss continues. Susceptibility to extinction The characteristics of species particularly susceptible to extinction are: large body size (Bengal tiger, lion and elephant); small population size and low reproductive rate (Blue whale and Giant panda). Feeding at high trophic levels in the food chain (Bengal tiger and Bald eagle), fixed migratory routes and habit (Blue whale and Whooping crane) and localized and narrow range of distribution (woodland caribou; many island species) also make the species susceptible to extinction. 6