Open course in Zoology Unit II Threats to wild life

Unit II Threats to wild life

Living things face a constant barrage of external stresses or threats that challenge their ability to survive and reproduce. If a species is unable to successfully cope with these threats through adaptation, they may face extinction.

1)Habitat destruction( Qualitative and Quantitative): Habitat destruction is the main cause for wildlife extinction in India. The rapid deterioration of the environment due to human interference is aiding the disappearance of wildlife from the biosphere. According to IUCN, habitat loss and degradation have affected about 89 percent of all threatened birds, 83 percent of mammals and 91 percent of all threatened plants globally. Habitat loss is due to deforestation for extended cultivation, construction of dams, mining operations and road laying. When the natural habitat of animals is destroyed, it leads to a decline in their primary food supply and breeding and nesting grounds. Hence their numbers get drastically reduced. In the case of plants, if their natural habitat is destroyed and the species that controls the pests that attack them are lost, then their survival is at risk. 

With the advent of agriculture man began to grow large quantities of selected crops in his own chosen place, after clearing away the existing natural ecosystem. Out of thousands of edible plants on earth, we have come to depend on only a few. About 90% of the plant food that we eat comes from only twenty species and more than half comes from just three grains, viz., rice, wheat and corn. Selective cultivation has paved the way for the disappearance of wild and rare species. As a result we have lost much of the faunal diversity that depended on those species. Large scale use of pesticides and fertilizers has polluted the land and river ecosystems. 

2)Isolation of population and inbreeding depression: As humanity spreads out over the globe, finding ever more clever ways to domesticate wild landscapes and harness natural processes to its will, many species of wildlife find their natural distributions becoming fragmented.  Iconic North American species such as grizzly bears, red-cockaded woodpeckers, and the American burying beetle today inhabit only small fractions of the ranges they occupied only 100 years ago. A result of this fragmentation is that many individuals exist in small, isolated populations.  In these populations, a curious phenomenon known as inbreeding depression operates, and it refers to the decline in average fitness of individuals in a shrinking population.

Inbreeding depression is essentially a result of individuals in small, isolated populations being more likely to mate with close relatives.  It’s well known that mating with close relatives produces less fit offspring, and the aggregate effect in natural populations is seen as low average fitness and an ensuing low population growth rate.  This can be a serious problem in populations subject to conservation efforts because even after protective measures have been taken (removing threats, restoring habitat) recovery can be hindered by inbreeding depression.  

3)Hunting and Poaching: Hunting, killing and selling (or using) of wildlife species for monetary or materialistic gains is how one describes Poaching .Poaching of animals for their skin, fur, tusk, horns and meat for medicinal purposes are a major threat to birds, mammals, plants and reptiles. Superstitious beliefs are the cause for the slaughter of certain species. The meat or body parts of these animals are believed to cure particular ailments. 

4)Wild life trade :Wildlife is vital to a high proportion of the world's population. People depend directly on wildlife for consumption and as a way of earning cash. However, irresponsible wildlife trade is threatening this resource, and those most affected tend to be the poorest people, in developing nations.Illegal wildlife trade causes additional problems. The species traded are often already highly threatened and in danger of extinction, conditions under which wildlife is transport are often appalling, operators are unscrupulous and do not care how they damage the environment(for example they use cyanide to kill fish, or log in protected areas; illegal trade undermines nations' efforts to manage their natural resources sustainably and causes massive economic losses in lost earnings. It is often said that illegal wildlife trade is the third most valuable illicit commerce behind drugs and arms.

Introducing invasive species that prey upon, or out compete native species. Invasive species are a major cause of recent extinctions. Wildlife traders have purposely introduced many invasive species, such as American Mink, Red-eared Terrapin and many plant species.

Invasive species are one of the leading threats to native wildlife.Approximately 42% of Threatened or Endangered species are at risk primarily due to invasive species. An invasive species can be any kind of living organism—an amphibian (like the cane toad pictured left), plant, insect, fish, fungus, bacteria, or even an organism’s seeds or eggs—that is not native to an ecosystem and which causes harm.  They can harm the environment, the economy or even, human health. Species that grow and reproduce quickly, and spread aggressively, with potential to cause harm, are given the label of “invasive”.

Eg.Invasive plants

1)Lantana camara is a significant weed of which there are some 650 varieties in over 60 countries. It is established and expanding in many regions of the world, often as a result of clearing of forest for timber or agriculture. It impacts severely on agriculture as well as on natural ecosystems

2)Mikania micrantha is a perennial creeping climber known for its vigorous and rampant growth. It grows best where fertility, organic matter, soil moisture and humidity are all high. It damages or kills other plants by cutting out the light and smothering them.

Eg.Invasive animals:

1)African Cat fish: African cat fish Clarias gariepinus for aquaculture purposed is posing a threat to indigenous catfishes in our rivers

2)Tilapia: Tilapia is threat to native species through competition for food and nest space. Juveniles have been documented to feed on other fish.

Extict Animals:Causes of Extinction:

·         Deforestation and encroachment and habitat distruction

·         Over exploitation

·         Poaching and wildlife trade in animals

·         Climatic changes have immensely affected the living beings.

·         Introduction of non-native species into the new habitats have threatened the existence of native species

1:The dodo

The dodo bird inhabited the island of Mauritius in the Indian Ocean, where it lived undisturbed for so long that it lost its need and ability to fly. It lived and nested on the ground and ate fruits that had fallen from trees. There were no mammals on the island and a high diversity of bird species lived in the dense forests.In 1505, the Portuguese became the first humans to set foot on Mauritius. The island quickly became a stopover for ships engaged in the spice trade. Weighing up to 50 pounds, the dodo bird was a welcome source of fresh meat for the sailors. Large numbers of dodo birds were killed for food.Later, when the Dutch used the island as a penal colony, pigs and monkeys were brought to the island along with the convicts. Many of the ships that came to Mauritius also had uninvited rats aboard, some of which escaped onto the island.Before humans and other mammals arrived the dodo bird had little to fear from predators. The rats, pigs and monkeys made short work of vulnerable dodo bird eggs in the ground nests.The combination of human exploitation and introduced species significantly reduced dodo bird populations. Within 100 years of the arrival of humans on Mauritius, the once abundantdodo bird was a rare bird.The last dodo bird was killed in 1681.

2:Passenger pigeon.( Ectopistes migratorius.):This was a species with well-developed social tendencies. Millions of these birds roamed the great eastern forests of North America feeding on beech-nuts, acorns, and cultivated grains. Their flocks were so large that they were claimed to darken the sky. Hunters found them easy prey and an almost endless supply of meat, feathers and fat. From about 1850 large numbers of shot pigeons were transported to America's growing cities. Each female passenger pigeon laid only one egg a year. Their numbers were in sharp decline by the 1880s and by September 1914 they were extinct.

Distribution and population:Ectopistes migratorius was found forest in eastern and central Canada and the USA, occasionally wandering south to Mexico and Cuba. Over the 19th century, the species crashed from being one of the most abundant birds in the world to extinction (Schorger 1955). The last wild bird was shot in 1900, and surveys in 1910-1911 failed to record any (Blockstein and Tordoff 1985). The last captive bird died in 1914 in the Cincinnati Zoo (Wilcove 1989). It was a nomadic species, breeding and foraging in vast flocks millions of birds strong. It exploited seasonally available crops of beechmast, acorns and chestnuts; scouting for food sources and infomation sharing was likely to have required flocks of a certain critical size, below which survival would be compromised. Birds nested in April or May in vast colonies typically 16 by 5 km in size. 

3:Cheetah(Acinonyx jubatus):The fastest land animal in the world, the cheetah is a marvel of evolution. The cheetah's slender, long-legged body is built for speed. Cheetahs are tan in color with black spots all over their bodies. They can also be distinguished from other big cats by their smaller size, spotted coats, small heads and ears and distinctive "tear stripes" that stretch from the corner of the eye to the side of the nose.Cheetahs eat mainly gazelles, wildebeest calves, impalas and smaller hoofed animals.By the beginning of the twentieth century, the species was already heading for extinction in many areas. The last physical evidence of the Asiatic cheetah in India was three shot by the Maharajah of Surguja in 1947 in eastern Madhya Pradesh, a man also noted for holding a record for shooting 1,360 tigers. In India in the mid-20th century, prey was abundant, and cheetahs fed on the blackbuck, the chinkara, and sometimes the chitaland the nilgai. With the death of the last remaining population of the Asiatic cheetah in India, the species was declared extinct in India; it is the only animal in recorded history to become extinct from India due to unnatural causes. consequence of the extinction of the cheetahs and subsequently the Indian royalty that prized them was that their grasslands homes came to be controlled, used and managed by local people. "The grasslands faded and diminished under the hooves of a thousand cattle, they were tilled and ploughed until only a few scattered remnants were preserved in the form of wildlife sanctuaries.