Earth’s Biomes, The rule of climatic similarity

Earth’s Biomes

Biomes are regions of the world with similar climate, animals and plants such as desert, tropical rain forest, freshwater biomes, etc.

Knowledge of basic characteristics of the world’s major biomes and features of life within each is important for planning, dealing with environmental issues, and determining beneficial introduction of new species.

 The rule of climatic similarity

Why is one area of the Earth’s land surface a desert, grassland, and another a forest? Why do different types of these exist? The general answer to these questions is differences in climate, caused mostly by differences in average temperature and precipitation caused by global air circulation. Different climates promote different community of organisms.

Similar environments lead to the evolution of organisms similar in form and function and to similar ecosystems. This is known as the rule of climatic similarity and leads to the concept of the biomes.

There is a strong relationship between climate and life. The rule of climatic similarity is important in environmental science because by knowing the climate, we can predict a great deal about what kinds of life we will find in an area and what kinds could survive there if introduced.

Convergent evolution

A kind of evolution wherein organisms evolve that have similar structures or functions in spite of their evolutionary ancestors being very dissimilar or unrelated.

The process by which species evolve in different places or different times and, although they have different genetic heritages, develop similar external forms and structures as a result of adaptation to similar environments is known as convergent evolution.

Although geographically isolated for 180 million years, certain plants of the American and African deserts may look similar in spite of not being closely related and belonging to different biological families. Similar climates, to which these plants have been subjected, imposed similar stresses and opened up similar ecological opportunities. The plants evolved to adapt to these stresses and potentials and have come to look alike and prevail in like habitats. The ancestral differences between these look-alike plants can be found in their flowers, fruits, and seeds, which are evolutionarily the most conservative (least changing) organs and provide the best clues as to the genetic history of a species. People make use of convergent evolution when they move decorative and useful plants around the world.        

                                                   

Major biomes

Tundra, Boreal Forests or Taiga, Temperate Forests, temperate Rain Forests, Temperate Woodlands, Temperate Shrub lands, Temperate Grasslands, tropical Rain Forests, Tropical Seasonal Forests and Savannas, Deserts, Wetlands, Freshwaters, Intertidal, Open Ocean, Upwellings, Hydrothermal Vents, etc.

Tundra: Cold Boggy Plains of the Far North

Tundra are treeless plains that occur under the harsh climates of low rainfall and low average temperatures. The dominant vegetation includes grasses and their relatives (sedges), mosses, lichens, flowering dwarf shrubs, and mat-forming plants.

There are two kinds of tundra: arctic which occurs at high latitudes, and alpine, which occurs at high elevations. The vegetation of both is similar, but the dominant animals are different. Arctic tundra typically have important large mammals, birds, and insects; in alpine tundra, the dominant animals are small rodents and insects. Alpine tundra occupy comparatively small, isolated areas, whereas arctic tundra cover the large territories required for populations of large mammals.

Parts of tundra have permafrost, which is permanently frozen ground. Such area are extremely fragile ecologically; when disturbed by such activities as the development of roads, permafrost areas may be permanently changed or may take a very long time to recover. As the environment becomes more harsh, the vegetation grades from dwarf shrubs and grass like plants to mosses and lichens, and finally to bare rocks surfaces with occasional lichens. The extreme tundra occurs in Antarctica, where the major land organism in some areas is lichen that grows within rocks, just below the surface.

Taiga or Boreal Forests (Evergreen Forests of the North)

The Taiga biome includes the forests of the cold climates of high latitudes and high altitudes, covering approximately 11 % of the Earth’s land. Taiga forests are dominated by conifers, especially spruces, firs, and larches, and certain kinds of pines. Aspens and birches are important flowering trees. Boreal forests are characterized by dense stands of relatively small trees, typically under 30 m, which form dense shade and making walk difficult. Although cover very large areas, relatively few important species of trees occur in taiga. There are only about 20 major tree species in North American boreal forests, for example. Boreal forests are among the most economically important biomes as they are the source of much lumber and paper pulp.

The dominant animals of boreal forests include a few large mammals (moose, deer, wolves, and bears), small rodents (squirrels and rabbits), small carnivores (foxes), many insects, and migratory birds, especially water fowl and carnivorous land birds, such as owls and eagles.

Disturbances—particularly fires, storms, and outbreaks of insects—are common in the boreal forests. 

Tropical Rain Forests: Lush Equatorial Forests

Tropical rain forests occur where temperatures are warm throughout the year and precipitation occurs almost daily. The annual precipitation is typically from 200-450 cm. Much of this precipitation comes from locally recycled water that enters the atmosphere by transpiration of the forest’s own trees.

Of all the biomes, the tropical rain forests are unexcelled in species richness and variety. Hundreds of species of trees can be found within a few square km. Typically, some trees are very tall (some 50 m), but there are many kinds of plants; some, like palm trees remain relatively small (30-40 m); others, like bromeliads and some ferns, grow on trees. Many species of animals occur; mammals tend to live in trees but some are ground dwellers. Insects and other vertebrates are abundant and show a high diversity. Rain forests occur in some of the most remote regions of Earth and remain poorly known; many undiscovered species are believed to exist there.

Except for dead organic matter at the surface, soils tend to be very low in nutrients. Most chemical elements are held in the living vegetation, which has evolved to survive in this environment; otherwise, rainfall would rapidly remove many chemical elements necessary for life.

Unless strong conservation measures are initiated soon, human population growth and industrial expansion in tropical countries may spell the end of tropical rain forests by the end of the middle of the 21^st century. Biologists fear that many rain forest organisms will become extinct before they have even been identified and scientifically described. 

Deserts are dry areas found in both temperate (cold desert) and subtropical or tropical regions (warm desert) where the rainfall is less than 50 cm/yr. Most deserts have a considerable amount of specialized vegetation, as well as specialized vertebrates and invertebrates. Soils often have abundant nutrients but little or no organic matter and need only water to become very productive. Disturbances are common in the form of occasional fires, cold weather, and sudden, infrequent, and intense rains that cause flooding.

The dominant animals of warm deserts are nonmammalian vertebrates (snakes and reptiles). Mammals are usually small, like kangaroo mice of North American deserts.

Fresh waters

Although fresh water lakes, ponds, rivers, and streams make up a very small portion of Earth’s surface, they are critical for our water supply for homes, industry, and agriculture and play important ecological roles. They are major recreational resources but are easily polluted. Dominant plants are floating algae, referred to as phytoplankton. Along shores and in shallow areas are rooted flowering plants, such as water lilies. Animal life is often abundant. Open waters have many small invertebrate animals (zooplankton)—both herbivores and carnivores. Many species of finfish and shellfish are found.

Rivers and streams are important in the biosphere as major transporters of materials from land to ocean. Fresh waters are economically important to people for their drinking water, production of energy, fish, bird life, and for recreation and transportation.

Estuaries—areas at mouths of rivers where river water mixes with ocean waters—are rich in nutrients and usually support an abundance of fish. They are important as breeding sites for many commercially significant fish.

Human activities have several adverse impacts on rivers and streams, including water pollution and the effects of dams, which are built to contain or divert the water of rivers or streams. Pollution alters the physical environment and changes the biotic component downstream from the pollution source. A dam causes water to back up, flooding large areas of land and forming a reservoir, which destroys terrestrial habitat. Below the dam, the once powerful river is often reduced to a relative trickle, altering aquatic ecosystems.

Open Ocean

The open ocean biome includes open waters of much of the oceans. These vast areas tend to be low in nitrogen and phosphorus—chemical deserts with low productivity and low diversity of algae. Many species of large animals occur but with low density.