Communities

Organisms live together in assemblages called communities. Some communities are very small, such as those composed of invertebrates and decomposers living within a rotting log. Others may be as large as an entire forest. The most extensive communities, called Biomes, occupy wide geographic areas.

The major biomes are arctic tundras, northern coniferous forests, deciduous forests, grasslands, deserts, tropical jungles and rain forests.

Chapparals (shubby forests) and coniferous rain forests are sometimes also considered biomes. The distinctive appearance of each biomes is generally determined by the predominance of characteristic plant species, but the animals that are characteristically associated with it also contribute to its distinctiveness.

Communities are composed of both plants and animals. Each species is distributed according to its own biological requirements, which may be affected by other species. For example, sugar maple seedlings required shade and may therefore mature easily in dense forests, whereas seedlings of eastern white pine require full sunlight for vigorous growth. Therefore, some species are sometimes associated with each other, but the exact degree of dependence is difficult to determine and has led to differences of opinion concerning th extent to which communities are discrete entities. By tabulating all plants found along a line passing through adjacent communities on mountainsides, it has been shown that the distribution pattern of each species is independent of most others, suggesting a continuum rather than a few discrete communities.

Communities also exhibit vertical stratification or layering in tropical rain forests, for example the tallest trees, called emergents, grow above the canopy trees; below the canopy trees are shorter trees; below the shorter trees are shrubs; and covering the forests floor is a layer of herbaceous (nonwoody) plants growing in soil inhabited by fungi and bacteria. Some charcteristic animals are also found in each of the strata, such as toucans in the canopy, but most animlas range trhough several strata.

Another aspect of communities is temporal (time) structure.

Some species of animals, are diurnal (active in daytime), some are nocturnal (active at night), and still others are crepuscular (acitve at twilight hours). This structure allows more organisms to occupy the same area without interfering with each other. In addition to these daily activity patterns, there may also be seasonal ones. In temperate areas, for example, frogs of different species use ponds to reproduce at various times throughout the spring. This prevents excessive competition between species for space and food at any one time.

The number of species within a community is called species diversity, Species diversity has two components, richness and evenness. If there are many species in a community, it is said to have a rich diversity. All species, however, are not always equally represented. If, as commonly happens, only a few species are abundant, the diversity is said to be uneven. If a community is made up of many species and each is relatively stable, because the reduction or removal of any one species would be far less important than the loss of an abundant species in a community where only a few are numerous.

If a community that has been disturbed by a disaster such as fire, flood, windstorm, volcanic eruption, plow, or bulldozer, is left undisturbed for a long time, it will eventually restore itself; this process is called succession. A forest completely destroyed by fire may take hundreds or thousands of years to become completely renewed, depending on the climate, the nature of the soil, and other environmental factors. A forest destroyed by fire in Minnesota might be restored in a few hundred years, whereas one in Mexico destroyed by a lava flow might not be restored for thousands of years. Succession also occurs very slowly in the desert and in the tundra because of climatic and soil condition.

The first species to invade a destroyed area are called pioneers. These opportunistic species usually have good means of dispersal and high reproductive capacities. Lichens, grasses, and other herbaceous species are the most common pioneers, but trees such as cottonwood, elm, aspen, and silver maple, which produce abundant windblown seeds, are sometimes found as well. Availability of sources of spores of seeds at the periphery of the disturbed area, as well the suitability of the disturbed site for each species, determines the species composition of the first community formed. THe invading species begin to change the environment by increasing the organic content of the soil with their dead parts and excreted wastes, creating shade, and changing moisture conditions. Some species harbor nitrogen-fixing bacteria that release nitrogenous compounds into the soil and thereby fertilize it.

In the course of succession, conditions are generally made more suitable for new types of organisms that use less energy for reproduction and more energy to maintain themselves. 
These species gradually win out in competition with the pioneers. Collectively, they produce a new community. The process of replacement of species may continue for a long time, the changes occur gradually. Eventually a point is reached at which the environmental and species changes are minimal and species diversity is high. This relatively stable community is called a climax community.

Protective Measures

Many endangered species received a measure of relief in 1973 (first of protective measures has been arrange), when the 80 nations that originally participated in the Convention on International Trade in Endangered Species of Wild Flora and Fauna in Washington D.C., agreed to halt imports of endangered species. In the same year, the United States Congress enacted the Endangered Species Act, ensuring the protection of the vital habitat of any endangered species. The act has been extended repeatedly since then. In 1972 the United Nations Conference on the Human Environment, held in Stockholm, Sweden, called for a 10-years moratorium on whaling. The following year the 14 nations in the International Whaling Commission, which meets annually to set quotas, rejected the recommendation but did reduce quotas, introduce area quotas for sperm whales, and continue to forbid the hunting of blue, bowhead, humpback, gray, and right whales. Various quotas have since been established. As a result of another conference held in 1972, an agreement to prohibit dumping of toxic materials in open seas was signed by 91 nations.

National parks throughout the world are often havens for threatened organism according to the protective measures. Research stations have been set up to replenish breeding stock and discover more about the environment and its interrelationships. The protective measures of endangered species are : 

Pesticide pollution endangers the bald eagle (4), peregrine falcon (6) and Japanese white stork (8)
Oil spills threaten the puffin (3)
Water pollution has also led to the decline of the North Atlantic salmon salar (1), Atlantic sturgeon (2), manatee (5) and black footed penguin (7)

Animal threatened by introduced predators include the Galapagos giant tortoise (9), kakapo (10),
a New Zealand ground parrot (11), kagu (12), Indian wild ass (13)
Cattle plague affects the western giant eland (14)

Superstitions endanger such animals as the aye-aye (15), which some Madagascans regard as an evil spirit.
Horns of the black rhinoceros (16), and sika deer (19), are thought to have aphrodisiac properties.
The Japanese giant salamander (17), and formosan serow (18) are used for healing.

The Capture and collection of animals for zoos, pets, or research threatens populations of the Philippine monkey-eating eagle (20), orang utan (21) of Borneo and Sumatera, golden marmoset (22), giant anteater (23),
Texas blind salamander (24), Mediterranean spur-thighed tortoise (25) and golden frog (26) of Panama.

Hunting and over exploitation include the dugong (27), bengal and siberian tiger (28), L. tigris altaica (29), several subspecies of leopard (30), the arrau (31), Atlantic Walrus (32), blue whale (33), European beaver (34),
Nile crocodile (35), green turtle (36), American alligator (37), wild yak (38), chincilla (39), snow leopard (40).

Shooting for "sport" has endangered many species. The giant sable antelope (41),
The Arabian ostrich (45), the Arabian oryx (43), Grus Americana (42), the trumpeter swan (44), Canada goose (46), California condor (47), and polar bear (48)

Many native species are considered pests or predators of introduced species in the new habitats created by human settlement. Animals persecuted for this reason include the Tasmanian wolf (49), wolf (50), black-footed ferret (51), Spanish imperial eagle (52), Mexican grizzly bear (53), Hawaiian hawk (54), Spanish lynx (55), sea otter (56), northern kit fox (57), Florida cougar (58), and Asiatic lion (59).

Deforestation, wetland drainage and other forms of habitat destruction have to the decline of white -throated wallaby. Macropus parma (60), mountain gorilla (61), indri indri (62), Salmo clarki (63), Komodo dragon (64), chimpanzee (65), Everglade kite (66), Hawaiian gallinule (67), Indian elephant (68), spider monkey (69), Comanche Springs pupfish (70), and British swallowtail butterfly (71).

Endangered Species

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Endangered species are those whose populations have been so reduced that they are threatened with extinction. Thousand of species are included in this category. The international Union for the Conservation Of Nature Resources (headquartered in Morges, Switzerland) publishes a list of threatened mammals, birds, reptiles, and amphibians. This list is growing at an alarming rate, as is the number of endangered species of fish, invertebrates, and plants.
During the millions of years that preceded the appearance of human life, extinction of organisms was linked to large scale geologic and climatic changes, the effects of which were translated into major alteration of the environment. Environment change is still the primary cause of the extinction of animals, but now the changes are greatly accelerated by human activity. Clearing land for farms and towns, lumbering, mining, building dams, and draining wetlands all alter the environment so extensively that ecosystems may be completely destroyed. With a burgeoning human population requiring food, shelter, and clothing and constantly demanding more energy using devices, the temptation to exploit land for human use without regard for consequences is great.
Frequently, several forms of environmental change are responsible for the disappearance of species. For example, as tropical forests are cut down, primates have progressively smaller feeding and living spaces. They also become more accessible to hunters, who kill monkeys for food and trap many primates for sale as pets, research animals, and zoo specimens. Some animal species may move into human communities when their own are destroyed. Extermination of marauding monkeys, roaming tigers, or foraging deer is easy to justify by people whose livelihood is threatened.

Ecology

Ecology is the scientific study of the interrelationships of plants, animals, and the environment. In recent years, the word has sometimes been misused as a synonym for environment. The principles of ecology are useful in many aspect of the related fields of conservation, wildlife management, forestry, agriculture, and pollution control.
The world ecology (Greek, oikos, "house," and logos, "study of") is generally believed to have been coined by Ernst Haeckel, who used and defined it in 1869. The historical roots of ecology lie not only in natural history, but in physiology, oceanography, and evolution as well. It has occasionally been called scientific natural history (a phrase originated by Charles Elton) because of its origin and its heavy reliance on measurement and mathematics. Ecology is variously divided into terrestrial ecology, fresh-water ecology (limnology), and marine ecology, or into population ecology, community ecology, and ecosystem ecology.


Ecological Classification of Organism
Ecologists commonly classify organisms according to their fucntion in the environment. Autotrophs ("self-nourishers," also called producers), which are mainly green plants, manufacture their own food from carbon dioxide, water, minerals, and sunlight, whereas heterotrophs - a wide assortment of organisms - lack the metabolic machinery to synthesize their own food and must obtain it from other sources.
Some heterotrophs - the herbivores - eat plants, and some - the carnivores, or predators - eat animals. Some, called omnivores, eat both plants and animals; others eat only dead plants and animals. Some, called scavengers, eat large dead organisms. Some smaller heterotrophs, such as bacteria and fungi, feed on dead organisms; they are called decomposers. Parasites eat living organisms, but, unlike predators, do not devour them at one time. Parasite include forms such as ticks and fleas, which live on their hosts, and others, such as tapeworms, roundworms, and bacteria, which live within their hosts.

Related Topic :
Communities
Endangered Species