English Arabic French German Hindi Italian Portuguese Russian Spanish

Biodiversity decline causes concern

AddThis Social Bookmark Button



Saturday, February 2, 2013



Overuse of forest in Satchari National Park, Habiganj-Sylhet

Dr. M.a. Bashar



Biodiversity almost always refers to the diversity of species found in a given ecosystem. These are its structural components. Identifying the structural components is important, because function flows from structure, and it is the functioning ecosystem that provides the goods and services sustaining human life and enterprises. Can ecosystems lose some species and still retain their functional integrity? Research evidence indicates that it is the dominant plants and animals that determine major ecosystem processes such as energy flow and nutrient cycling.


How much biodiversity of species is there? Estimate ranges widely, and the fact is, no one knows. At least 726 animal and 90 plant species have become extinct since 1500. Most of the known extinctions of the past several hundred years have occurred on oceanic islands, where small land masses limit the size of populations and human intrusions are the most severe.


Global Biodiversity Outlook published in 2001 by UNEP to provide information on Biological Diversity, estimated that some 24% of mammal (1,130) and 12% of bird species (1,183) are globally threatened. There were many causes for the decline of biodiversity. Biologists have identified some of them as more responsible. These are physical alteration of habitats, population connection, pollution, exotic species, and overuse.


Physical alteration of habitats

When a forest is cleared, for example, plant and animal that occupied the destroyed ecosystem, also suffers. The idea that this wildlife simply will move “next door” and continue to live in an undisturbed section is erroneous.


Human-dominated landscapes, however, consists patches that frequently contrast highly with neighbouring patches. For continued survival of any natural population, the number of individuals must never fall below a critical line, and that requires a certain minimum area that must be large enough to compensate for years of adverse weather. For many species, more area will be required during a dry year than during a normal year. If development reduces the habitat to a point where it cannot support the critical number during an adverse year, the entire population will perish.


Streams are sometimes “channelized” their beds are cleared of fallen trees and riffles, and sometimes the stream is straightened out by dredging. Such alterations inevitably reduce the diversity of fish and invertebrates that live in the stream.


Intrusion is one of the reasons to reduce biodiversity. Birds use the airways as highways. Recently, telecommunications towers have presented a new hazard to birds. Although television towers have been around for decades, new towers are sprouting up on hill-tops and countrysides in profusion. The lights often placed on these tower can attract birds which usually migrate at night, and the birds simply collide with the towers wires. Some 45,000 towers over 200 feet high are now in place, and the number is expected to double within a decade (The U.S. Fish and Wildlife Services 'FWS').The FWS has estimated that the towers kill somewhere between 5 and 50 million birds a year. In Bangladesh towers establishment is indiscriminately done and no estimation is yet made on the number of towers and also on the bird-killings occurred because of the tower placement.


Population connection

Past losses of biodiversity can be attributed to the expansion of the human population. Continuing human population growth will further alter natural ecosystems, resulting in the inevitable loss of more wild species. The losses will be greatest in the developing world, where biodiversity is greatest and human population growth is highest. Africa and Asia have lost almost two-thirds of their original natural habitat. In East Africa, where human population growth has been explosive for several decades, the conversion of Savanna and woodlands to cultivation or intensive grazing by goats and cattle has driven most of the African elephant population into the existing wildlife reserves, greatly reducing their numbers. The other large African mammals have experienced similar reductions, as the needs of the rural population inevitably conflict with those of the large wild animals of East Africa.


Pollution is a major factor that can directly kill many kinds of plants and animals, seriously reducing their populations. For example, nutrients (phosphorus and nitrogen) from America's agricultural heartland traveling down the Mississippi River have created a 7,700-square mile “dead zone” in the Gulf of the Mexico where oxygen completely disappears from depths below 20 meters every summer. Shrimp, fish, crabs, and other commercially valuable sea life are either killed or forced to migrate away from this huge area along the Mississippi and Louisiana coastline. This type of pollution in the aquatic ecosystem in Bangladesh is too severe, but yet no proper corrective attempts have been made. Buriganga river near Dhaka city has collapsed ecologically and become dead biologically long before. No plankton growth is there for lack of oxygen supply and increase of waste-deposition rate per year.


Pollution destroys or alters habitats, with consequences just as severe as those caused by deliberate conversions. Acid deposition and air pollution kill forests; sediments and nutrients kill species in lakes, rivers, and bays; and emissions cause depletion of the stratospheric ozone species. Global climate change, brought on by anthropogenic greenhouse gas emissions, is already having an impact on many species rates. In this case, however, the developing world, where population growth is such a problem, is not much to blame. Instead, global climate change and pollution from toxic substances are the legacy of the already developed nations.


Exotic species

An exotic species is a species introduced into an area from somewhere else, often a different continent. Such introduced species frequently stands unsuccessful in establishing viable population and quietly disappears. This is the fate of many pet birds, reptiles, and fishes that escape or are deliberately released from their native habitats. Occasionally, however, an introduced species finds the new environment very much to its linking and can become an invasive species, thriving, spreading out, eliminating native species by predation or competition for space or food. Exotic species are major agents in driving native species to extinction and are responsible for an estimated 39% of all animal extinctions since 1600.



Overuse is not only the excessive use but also indiscriminate use by the anthropogenic activities. Overuse is major assault against wild species, responsible for 23% of their recent extinctions. Overuse is driven by a combination of greed, ignorance, and desperation. The plight of birds in Europe is a good example. In Greece, some 700,000 birds are shot each year. In Malta about 3 million a year are killed and eaten each year. Another prominent form of overuse is the trafficking in wildlife and in products derived from wild species.


Bangladesh is a glaring example overuse of natural resources. Forests of the country are worst sufferers. Most vital examples may be cited the Sundarbans ecosystem and the some other forest ecosystem of Bangladesh. In Sundarbans forest areas major plants or dominating plants are pollinated by insects. The plants dominating the Sundarban ecosystems mostly are with entomophilous pollens. This means that the plants are dependent on the insects mainly on the bees for their pollinations. The mawallis (professional honey-collectors) are allowed to enter into the forest during the period of April to June every year. It is the high flowering period for the dominating plants. Plant-animal interactions in the mangrove ecosystem is to be attentively maintained otherwise this most suitable site for biodiversity maintenance will be perished even if we take other several measures to maintain it.


The Satchari forest in Habiganj, Sylhet is a newly overexploited and overused forest ecosystem and it is most alarming situation in the country. The visitors are indiscriminately allowed to the forest. The damage made by the situation stands unreparable. One example could given here. One year ago, 15 “spot-hedges” were identified where the largest butterflies of Bangladesh (Birdwings) were naturally colonized. “Spot-hedge” is the smallest area (small suitable ecosystem) in the forest where the butterflies get their all necessities both biological and environmental. Studies reveal that out of the 15 marked “spot-hedges” six have been destroyed because over-use of the forest as a whole. It is now found that the population of the bird-wing butterflies has been dropped by 50% in the present year.



Dr. M.A. Bashar is Professor, Department of Zoology, University of Dhaka.



Source: thedailystar







Add comment

Security code

| + - | RTL - LTR