Loss and Threats to Biodiversity-V Semester

 

Loss and Threats to Biodiversity

The loss of biodiversity and the related changes in the environment are now faster than ever before in human history  and  there  is no sign of  this process  slowing down.  Virtually all of Earth’s  ecosystems  have been dramatically distorted and altered by human activities and  continuously  be  converted  for  agricultural  and other uses. Many animal and plant populations have declined  in  numbers  and  geographical  spread.

However, species extinction is a natural part of Earth’s history but human activity has increased the extinction rate by at least 100 times compared to the natural rate. Loss of biodiversity is caused by a range of drivers. A  driver  is  any  natural  or  human-induced  factor  that directly  or  indirectly  causes  a  change  in an ecosystem. A  direct  driver unequivocally influences ecosystem  processes.  An  indirect  driver operates more diffusely by altering one or more direct drivers. Important direct drivers affecting biodiversity are habitat alteration, climate change, invasive species overexploitation and pollution.

 Principal threats to biodiversity

A threat by definition refers to any process or event whether  natural  or  human  induced  that  is  likely  to cause adverse effects upon the status or sustainable use of any component of biological diversity.  Biodiversity is  declining  rapidly  due  to  factors  such  as  habitat alteration and destruction by the land use change, over exploitation  of  biological  resources,  climate  change, pollution and invasive species. Such natural or human-induced factors tend to interact and amplify each other.

Habitat alteration and destruction

Overall, the  main factor  directly driving biodiversity loss worldwide   is   habitat   alteration   and  destruction.

Habitat destruction renders entire habitats functionally unable to support the species present in the habitat. Biodiversity reduced in this process when existing organism in  the  habitat  are  displaced  or  destroyed.

Human destruction of habitats has accelerated greatly in the latter half of the twentieth century. Natural habitats are often destroyed through human activity for the purpose of harvesting natural resources for industry production and urbanization. Clearing forest areas for agriculture, changes in the riverine habitat to lacustrine (reservoir) habitat by the construction of hydroelectric projects on the rivers, mining, logging, urban sprawl, construction of highways are some examples of habitat destruction and fragmentation. A five-year estimate of global forest cover loss for the years 2000–2005 was 3.1 percent.

In the humid tropics where forest loss is primarily from timber extraction, 272,000  km was  lost  out  of  a  global  total  of  11,564,000 km(or 2.4 percent). In the tropics, these losses also represent the extinction of species because of high levels of endemism. Increased greedy demand for resources has resulted into land use changes. Hence loss  to  genetic  diversity,  species  reduction  and increased  ecosystem  changes  such  as  random population  changes,  disease  outcrop,  and  habitat fragmentation  among  others  has  resulted  into biodiversity losses. 

 Over-exploitation of biological resources

This results when individuals of a particular species are taken  at a higher  rate than  can  be sustained by the natural reproductive capacity of the population being harvested. This can be through hunting, fishing, trade, food gathering etc. Overexploitation remains a serious threat  to  many  species,  such  as  marine  fish  and invertebrates, trees, and animals hunted for meat.  The grazing pressure on most of the high altitude grasslands of the Uttarakhand state both from migrant and local

communities, is the extensive extraction of medicinal herbs in these areas resulting in their over exploitation. Most industrial fisheries are either fully or overexploited, while destructive fishing techniques harm estuaries and wetlands. Although the true extent of exploitation is poorly known,  it is clear that rates of off take are extremely high in tropical forests. The trade in  wild   plants  and  animals  and  their  derivatives  is poorly   documented   but  is   estimated   at  nearly   $160 billion  annually. It ranges from live animals  for  the food and pet trade to  ornamental  plants and timber.

Because the trade in wild animals and plants crosses national  borders,   the   effort   to  regulate   it  requires international  cooperation  to  safeguard certain species from overexploitation. 

 Pollution

Over the past five decades, inorganic and organic pollutants have emerged as one of the most important factor of biodiversity loss in terrestrial, aquatic- marine as well as freshwater  ecosystems. Thermal pollution is another threat to biodiversity.  The potential consequences of organic pollutants in a freshwater ecosystem include eutrophication of fresh-water body, hypoxia in coastal marine ecosystems, nitrous oxide emissions contributing to global climate change, and air pollution by NO in urban areas. Occurrence of such problems varies widely in different regions. Species in habitats are  increasingly  being harmed  by  industrial activities  and pollution  from excessive  use of agro-chemicals such as DDT, oil spills, acid precipitation etc.

 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 pellet that fall into lakes and marshes.

The vulture was once very common in the Gangetic plains of India, and often seen nesting on the avenue trees within large cities in the region. Before the 1990s they   were  even   seen  as   a  nuisance,   particularly  to aircraft  as  they  were  often  involved  in bird strikes. The vulture has suffered a 99% population decrease in India and become rare due to poisoning by DDT used as pesticides and also by diclofenac which is used as veterinary non –steroidal anti- inflammatory drug, leaving traces in cattle carcasses which when fed by vultures leads to thinning of egg shells resulting into premature hatching and kidney failure in birds.

The dramatic decreases in house sparrow population in India is experienced in recent past. It is linked with pollution  caused  by  electromagnetic  radiation  from mobile  phones.  Microwave  towers;  the  excessive  use  of  pesticides,  a gradual decrease in nesting sites caused by changes in urban building design. 

 Species invasions    

This can be intentional or accidental.  Species introduced in an ecosystem will cause changes in the ecosystem. Introduced species are organisms arising in areas/ habitats in which they were previously not native. Such introduced species are usually referred to as biological pollutants. Some of the ecological impacts of the invasion include hybridization, out competition, disruption   of  original  ecosystem,  plant  pathogenic influences,   disease  transmission,   disruption   of  food-webs, and to some situations extinction. Species may be introduced intentionally for ornamental concerns, agriculture, hunting and spotting  activities, biotechnology for scientific research and for trade.

 Climatic changes

This is of great concern especially when global CO2 increases in the atmosphere resulting to global warming. Most species originate within a very narrow physiological limit; hence nature has a range of tolerance maintained for ecosystem stability. Changes may  be   gradual  or  abrupt such  that  if  the  limit  is exceeded the upper or lower, species suffers extinction.                

Recent  changes  in  climate,  such  as  warmer temperatures   in   certain   regions,   have   already  had significant impacts on biodiversity and ecosystem.  They have affected species distributions, population sizes, and the timing of reproduction or migration events, as well as the frequency of pest and disease outbreaks. Projected changes in climate by 2050 could lead to the extinction of many species living in certain limited geographical regions. By the end of the century, climate change and its impacts may become  the main direct  driver of overall biodiversity loss. While the growing season in Europe has lengthened over the last 30 years, in some regions of Africa the combination of regional climate changes and human pressures have led to decreased cereal crop production since 1970.  Changes  in fish population have  also  been  linked  to  large-scale climate  variations  such  as  "El  Nino"  have  affected fisheries off the coasts of South America and Africa, and decadal oscillations  in the  Pacific have affected fisheries  off  the  west  coast  of  North  America.

As climate change will become more severe, the harmful impacts on ecosystem services will outweigh the benefits in most regions of the world.  The Intergovernmental Panel on Climate Change (IPCC) project that the average surface temperature will raise by  2  to  6.4 levels.  This is expected to cause global  negative impacts  on biodiversity  (Millennium  Ecosystem Assessment, 2005).

 Population

From 1950 to 2011, world population increased from 2.5 billion to 7 billion and is forecast to reach a plateau of  more  than  9  billion  during  the  21st  century (Population   Reference   Bureau).    As  the  human population is increasing, there exists insatiable demand for raw materials which is bound to cause changes in biodiversity. The human population has more impact on biodiversity than any other single factor. According to Dumont, (2012) until the middle of the 21st century, worldwide losses of pristine biodiversity will largely depend  on  the  worldwide human  birth  rate .  It  is therefore vital to control human population which will result   in biodiversity conservation.