Biodiversity refers to “the sum total of all of the plants, animals, fungi, and microorganisms on Earth; their genetic and phenotypic variation; and the communities and ecosystems of which they are a part” (Dirzo & Raven, 2003) and is sometimes referred to as ‘species richness’. It is a concept of growing significance not only to ecologists but also to various governments. In essence, biodiversity reduces with extinction of species. Given the background extinction rates of 0.1-1.0 species per million species per year, for the last 300 years it is at least several hundred times the historical values. (Dirzo & Raven, 2003) From year 1500 to 2000 alone, 811 species have been recorded as extinct. I would like to discuss the relative importance of the major threats to global biodiversity.
Over-exploitation
The first important threat to global biodiversity is excessive exploitation by commercial hunting and illegal poaching, representing 23% of the known causes of animal extinctions in the past 400 years. (Chapman & Hall, 1992) Subsistence hunting is critical for charismatic mammals in tropical regions. (Dirzo & Raven, 2003) The recent misuse of the Internet for advertising and purchasing products derived from endangered species has allowed such wildlife trade to become ‘global’, which may render this threat more significant in the years ahead. The annual global wildlife trade is worth US$5 billion; this amount speaks for merchants who engage in activities ranging from slaughtering of elephants for their ivory, hunting of apes for ‘bushmeat’ at an unsustainable rate in Congo, to trading of tigers’ penises as aphrodisiac in China and other endangered species as pets, performers or decorative plants in Thailand. (Muench-Corbis et al, 2009)
Introduction of alien species
Contributing almost 40% of the extinction causes in the World Conservation Monitoring Centre's study (Chapman & Hall, 1992), the threat of non-native invasive species is even more important, triggering ‘domino effect’ in species removal if this occurs in ecosystems with interdependent species. Birds are the major victims in this category as an IUCN assessment found that this affects 30% of all threatened birds, 15% of the plants, but only 10% of the mammals. (Hilton-Taylor, 2000). On Hawaii alone, almost 100% of species are in danger of extinction attributable to introduced plants and animals. (Dirzo & Raven, 2003) The African Great Lakes - Victoria, Malawi and Tanganyika - are well-known for their great collection of endemic species, called "species flocks", of cichlid fishes. These endemic fish species are preyed on or their foods eaten after introducing a single exotic species, Nile Perch, intended for subsistence and sport fishing. (University of Michigan, 2006)
Habitat loss or degradation
Habitat loss, degradation or fragmentation, together with climate change, poses the most important threat to global biodiversity, although it represents only 36% of the extinction causes. (Chapman & Hall, 1992) Human encroachment by rampant deforestation for and pollutions from agricultural activities or infrastructural development destroy the habitats severely, in fact 89% of threatened mammals, 83% of birds and 91% of plants are affected according to the assessment of the IUCN. (Hilton-Taylor, 2000) From 1990 to 2005, the world lost 70 million hectares of forests, mostly in Brazil and India, which implies wherever “trees are lost, species soon follow”. (Muench-Corbis et al, 2009) What may be overlooked are fragmented or small lower-threshold habitats where species are more vulnerable to extinction owing to their inability to survive any environmental fluctuations (Travis, 2003) or migrate to another ecosystem. Tiny habitat islands, which are fragmented and isolated, embrace a lower threshold for extinction under the influence of climate change. In particular, species that needs a wider home range for hunting such as grizzly bear cannot survive in a small area or respond to climate change easily. Thus, such small-scale, isolated ecosystems cannot form a shelter for species to survive in habitat destroyed or degraded.
Climate change
Travis (2003) concluded using lattice models that species extinction is possible when they live below a threshold of a habitat of which the rate of climate change is a variable. Global warming will shift the climatic conditions characterising the present habitat belts either to higher latitudes or altitudes at a speed which species cannot respond. For example, Robert Colwell, a biologist at the University of Connecticut, in his survey of 2,000 species found that plants, insects, fungi species in the tropics fail to escape from rising temperature in their indigenous zones by migrating upward, north- or south-ward for cooler temperatures. (Walsh, 2008) Desiccated rainforests and warmer cool mountains in tropical zones will drive un-acclimatising species extinct. Examples are periled polar bear in Alaska and lost Golden Toad in cloud forests of Costa Rica, etc. (Walsh, 2008) In fact, up to one-third of existing species will face risk of extinction if the global temperatures increase 2-3°F above the current levels, according to the Intergovernmental Panel on Climate Change (IPCC). (Walsh, 2008)
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| Different colour in a lattice represents a different habitat. A climate window moving from (a) to (b) or (c) models on how global warming shifts the habitat regions of specific species to higher altitudes or latitudes to different extents. Species suffering from a habitat shift from (a) to (b) where some overlapping areas exist can still adapt to survive, but not from (a) to (c) directly. (Travis, 2003) |
The Value of Biodiversity
The recent National Ecosystem Assessment (NEA) in the UK says that ecosystems produce their own hidden wealth, such as food, health, clean water, clean air and cultural benefits. Valuing nature can be an important tool as we can use this to determine whether to preserve an ecosystem or not. In the UK, as much as 30% of our key ecosystems are degrading, while only 20% have improved, mostly related to air quality.
Green economics however, not only considers biodiversity important because of its various benefits discussed here, it also considers it important as an end in itself and not just a means. Valuation of nature is extremely difficult as different groups of people value different environments in wildly different ways. Moral and ethical questions can also be considered more important than the mere economics value of an ecosystem.
The way forward
In brief, over-exploitation, introduction of alien species and habitat loss, deteriorated by climate change, are the key threats to biodiversity globally. Given the magnitude of these threats, fixed, fragmented nature reserves plus other man-made barriers, such as cities and highways prevent migration of affected species for more suitable habitats. To facilitate migrations, conservation researches should focus on the strategy of creating ‘global nature pathways’ by reforestation connecting the existing reserves, in addition to mitigating climate change. This proposal is comparable to that of Walsh (2008) who suggested a ‘nature corridor’, by connecting forested areas, as in the case of Madagascar, allowing the migration of wildlife from tropical zones to the north/south or higher altitudes in search for more suitable habitats against rising global temperatures.
References
Chapman, & Hall. (1992). Global Biodiversity: Status of the Earths Living Resources. London: World Conservation Monitoring Centre.
Dirzo, R., & Raven, P. (2003). Global state of biodiversity and loss. Annual Review of Environment and Resources (28), 137-167.Hilton-Taylor, C. (2000). IUCN Red List of Threatened Species. Gland, Switzerland: World Conservation Union.
Muench-Corbis et al, D. (2009, April 2). Animals under siege. TIME Magazine .
Travis, J. M. (2003). Climate change and habitat destruction: a deadly anthropogenic cocktail. Proceedings B , 270 (1514), 467-473.
University of Michigan. (2006, January 4). Threats to Global Biodiversity. Retrieved November 1, 2009, from http://www.globalchange.umich.edu/globalchange2/current/lectures/biodiversity/biodiversity.html
Walsh, B. (2008, October 13). How climate change will impact animals. TIME magazine .
Email me at winstonkm.mark@googlemail.com
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