Environment and Ecology- Basic Concepts and its Types

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  • A layer of the Earth ’s atmosphere, above the troposphere, extends from 20 to 50 km above the sea level. Temperature increase throughout the stratosphere.

  • The Earth’s crust and a lower portion of the upper mantle, which together Earth ’s atmosphere a layer of strength, relative to the more easily deformable Asthenosphere below. On the basis of worldwide heat flow measurements,


Environment: The surroundings. The environment consists of natural environment and the cultural environment. The natural environment includes the nature of the living space (or land, soil and water), the chemical constituents and physical properties of the living space, the climate, and the assortment of other organisms present. The cultural environment or the phenomenal environment includes changes and modifications of the natural environment made by man. The effect of the environment on man is modified, in part, by the way the environment is perceived and human geographers distinguish this – the subjective environment – from the objective environment – the real world as it is. The objective environment is of less importance to the individual than his or her perceived image of it. A division may also be made between the built environment and the social environment which is made up of the various fields of economic, social, and political interactions.

The main concern of environmental geography is spatio-temporal analysis of environment in its totality and in the context of aggregate nature of place. It is basically a systematic study of biotic and abiotic attributes of ecosystems in the context of space and their mutual relationships as well as the spatial implications of such inter-relationships. The fundamental unit of study of environmental geography is the biosphere.

Modern environmental problems call for geographers to examine relations among Earth (environment/resources), society, and cultures through out space and time. Critical environmental concerns that are integral to physical geography include:

  • Global ozone depletion in the upper atmosphere that allows increasing amounts of ultraviolet radiation to reach Earth’s surface.
  • Possible global warming through human-caused increases of carbon dioxide in the atmosphere.
  • Worsening of air pollution, particularly in metropolitan areas.
  • Identification of natural hazards that threaten society, such as hurricanes, earthquakes, tsunamis, landslides, drought, and floods.
  • Deliberate destruction of Earth’s forests.
  • Increasing losses of plant and animal diversity as habitats disappear.
  • Spatial analysis of  disasters such as the 1986 Chornobyl’ nuclear power station and the March 2011 Tohoko earthquake of Japan.
  • Accounting for natural resources as environmental assets on national economic balance sheets.

Geography is in a unique position to synthesize the environmental, spatial, and human aspects of these concerns.


The layer of air surrounding the Earth, with a average composition, by volume  79% nitrogen, 20% oxygen, 0.934 % argon,  0.03 % carbon dioxide, and traces of rare gases (Fig.1.1). This surprisingly uniform composition is achieved by convection in the troposphere and by diffusion above it, especially above 100 km, where diffusion is rapid in the thin atmosphere, and stirring is weak. Also present are atmospheric moisture, ammonia, ozone, and salts and solid particles. The atmosphere is commonly divided into the troposphere, the stratosphere, the mesosphere, ionosphere,  and thermosphere.

The modern atmosphere is a gaseous  mixture of ancient origin. The principal substance of this atmosphere is air, the medium of life as well as a major industrial and chemical raw material. Air is a simple additive mixture of gases that is naturally odorless, colourless, tasteless, and formless, blended so thoroughly  that it behaves as if were single gas.

On the basis of composition  of gases  the atmosphere may be divided into (i) Heterosphere, and (ii) Homosphere.
On the basis of temperature the modern atmosphere may the divided into: (i) Troposphere, (ii) Stratosphere, (iii) Mesosphere, (iv) Exosphere)

1.Troposphere: The lower layer of the atmosphere is known as troposphere. It is the home of biospheric layer that supports life on Earth. Approximately 90 % of the total mass of the atmosphere and the bulk of all water vapour, clouds, weather, and air pollution are contained  within the troposphere. The tropopause is the upper limit which is defined by an average temperature of -57oC, but its exact elevation varies with the season, latitude, and surface temperatures and pressure. Near the equator, because of intense heating from below, the tropopause occurs at 18 km; in the middle latitudes, it occurs at 13 km and at the North and South Poles it is only 8 km or less above Earth’s surface. In the troposphere temperatures decrease with increasing altitude at an average of 6.4oC per k which is known as the normal lapse rate (Fig.1.2).

2.Stratosphere and Ozonosphere: A layer of the Earth’s  atmosphere, above the troposphere, extends from 20 to 50 km above the sea level. Temperature increase throughout the stratosphere. The heat source in the other functional layer, called the ozonosphere, or ozone layer. Ozone is a highly reactive oxygen molecule made up of three oxygen atoms (O3) instead of the usual two (O2)  that make up most oxygen gas. Ozone absorbs wavelength of ultraviolet light and subsequently eradicates tat energy at longer wavelengths, as infrared (heat) energy. Through this process, most harmful ultraviolet radiation is effectively ‘filtered’ from the incoming solar radiation, safeguarding life at Earth’s surface and heating the stratosphere.

3.Mesosphere: The mesosphere is the area from 50 up to 80 km. Its upper boundary, the mesopause, is the coldest portion of the atmosphere, averaging -90OC. It is characterized with continent-sized windstorms in the mesosphere. The very rarefied air is moving in vast  waves at speed in excess of 320 kmph. The importance of this new discovery to surface weather patterns and to the Earth-atmosphere energy budget is being considered.

4.Thermosphere ( Heat Sphere): That part of the atmosphere, starting at about 80 km above the sea level, the top of the mesosphere, extending to the uttermost fringe (480 km) of the atmosphere. Here temperatures increase with height.  High temperatures are generated in the atmosphere because the gas molecules absorb shortwave solar radiation.

The temperature curve in Fig.1.2 shows that temperatures rise sharply in the thermosphere, up to 1200oC and higher. Despite such high temperatures, the thermosphere is not ‘hot’ in the way you might expect. Temperature and heat are two different things. The intense solar radiation in this portion of the atmosphere excites individual molecules and atoms (principally nitrogen and oxygen). This kinetic energy, the energy of motion, is the vibrational energy that we measure, stated as temperature. However, the density of the molecules is so low that little actual heat is produced (heat is the quantity of thermal energy). Heating in the lower atmosphere near Earth’s surface is different because the greater number of molecules in the denser atmosphere transmit their kinetic energy as sensible heat, meaning that can sense it.
Ionosphere: The atmosphere has two functional layers, so called because both function to filter harmful wavelengths of solar radiation, protecting Earth’s surface from bombardment in any significant quantity. The upper functional layer, the Ionosphere, coincides with the thermosphere. It is composed of atoms that acquired electrical charges when they absorbed cosmic rays, gama rays, X-rays, and shorter wavelengths of ultraviolet radiation. These charged atoms are called ions, giving the ionosphere its name. Radiation bombards the ionosphere constantly, producing a constant flux (flow) of electrons and charged atoms.

Earth’s Four Spheres Earth’s surface is where four open systems interface and interact (Fig.1.3). IT may be seen from 2.1 that the three abiotic (non-living) systems are overlapping to form the realm of biotic (living) system. The abiotic spheres are the atmosphere, hydrosphere, and lithosphere. The biotic sphere is called the biosphere. Because these four spheres are not interdependent units in nature, their boundaries must be understood as transitional rather than sharp delimitations.

Hydrosphere: The Earth’s water, which exists in both fresh and saline form and may occur in a liquid, solid or gaseous  state. Land, sea and air each contribute to the total volume of water, which is conveyed between various locations and transformed from one state to another (Hydrological Cycle). The overall quantity of water in the hydrosphere remains more or less constant.
About 71 per cent of Earth’s surface is occupied by water. Some 97.3 per cent of its volume is currently in the ocean, the maximum extent of which is in the Southern Hemisphere. Of the 2.7 percent terrestrial water, most is polar snow and ice. Groundwater (the majority below soil level) is in lakes and rivers, living organisms.

Lithosphere: The Earth’s crust and a lower portion of the upper mantle, which together constitute a layer of strength, relative to the more easily deformable Asthenosphere below. On the basis of worldwide heat flow measurements, it has been estimated that the lithosphere varies in thickness from only a few kilometers along the crest of mid-ocean ridges where, according to the Plate Tectonics model, new lithosphere is being created, to over 300 km beneath some continental areas. Oceanic lithosphere capped by continental crust tends to be thinner but more dense than  continental lithosphere, which is capped by continental crust.

Biosphere: The zone, incorporating elements of the hydrosphere,  lithosphere and atmosphere, in which life occurs on Earth.  It is the intricate, interconnected web that links all organisms with their physical environment is known as biosphere (ecosphere).  The biosphere extends from the bottom of ocean trenches to about 8 km )5 miles0 into the atmosphere.The term is occasionally used to refer only to the living component alone, although it is more commonly conceived as a zone of interaction between the other ‘spheres’. This is appropriate, because life is dependent up on energy, processes and materials which are located in all three of the Earth’s other conceptual spheres, to the extent that the scheme is often represented as a series of overlapping circles with the biosphere in the nodal position. Used in this way, biosphere is synonymous with ecosphere.

The biosphere has evolved, reorganized itself at times, faced extinction, gained new vitality, and managed to flourish overall. Earth’s biosphere is the only one known in the Solar System; thus, life as we know is unique to the Earth.
Today, over seven hundred million humans, approximately one million animal species and 355,000 known plant species depend on the air, water and land of the planet Earth.
Ecology: The scientific study of the interactions between organisms and their environment. Ecology examines the relationships between organisms belonging to both the same and different taxonomic groups, and between those organisms and their physical environmental circumstances. The  word was first used by Ernst Haeckel in  1869, but many of its concepts are much more recent. The ecosystem concept is central to an understanding of the nature of ecological relationships and dates from the 1930s syntheses of Arthur Tansley. Still other associated concepts, such as those developed in relation to population ecology, came  much , so that ecology can be considered as a relatively new scientific discipline. 

Ecosystem: The North American ecologist E.P. Odum defines an ecosystem as ‘any unit that includes all of the organisms in a given area interacting with the physical   environment so that a flow of energy leads to …. Exchange of materials between living and non-living parts of ecosystems’.  This simplifies the earlier definition given by A.G. Tansely, who coined the term in 1935, and confirms the concept of the ecosystem in an aggregative hierarchy. Individuals aggregate into populations, populations come together in communities, and a community plus its physical environment comprise an ecosystem.

Ecological Transition: This concept was developed by Bennett in 1976, which concerns the reduction in the farmer’s dependence on his land that often accompaniers his incorporation into the cash economy. The economic opportunities of industry or urban life gradually provide viable  social alternatives to rural life and individual farmers can afford to be less concerned about the possibility of long term decline in the productivity of their land. Over-cultivation may result from this reduced ecological sensitivity in rural  population.
Ecological explosion: Ecological events marked by an enormous increase in number of some kind or kinds or organism. The term was defined by Elton in 1958 and was employed to indicate the bursting out from control of populations that were previously held in restraint by other forces. Classic examples of such explosions are found in the epidemics of infectious viruses and bacteria, such as influenza and bubonic plague, etc.

Many organisms  subject to such population outbursts are serious agricultural pests, such as desert the desert locust (Schistoverca gregaria). The causes of the devastating plagues appear to be related to weather conditions, particularly to moisture, operating in and through the process of phase transformation, in which the locusts exhibit polymorphism, changing from solitary (solitaria) forms to  gregarious or swarming forms (gregaria). The causes of  many ecological explosions remain far from clear and it is interesting to observe that many species which are rare in their normal  habitat experience such bursts of population when spread by man to new areas and environment.

Ecotone: The transition on the ground between two plant communities. It may be a broad zone and reflect a gradual blending of two communities or it may be approximated by sharp boundary line. It may coincide with changes in physical environmental conditions or be dependent on plant interactions, especially competition, which can produce sharp community boundaries even where environmental gradients are gentle. It is also used to denote a mosaic or interdigitating zone between two more homogeneous vegetation units. They have special significance for mobile animals through edge effects (such as the availability of more than one set of habitat within a short distance).

Ecotope: The physical environment of a biotic community (biocoenosis). It includes those aspects of the physical environment that are influences on or are influenced by a  biocoenosis. Together with its biocoenosis, the ecotope forms an integral part of biogeoecoenosis. There are two major component parts of the ecotope: the effective atmospheric environment (climatop) and the soil (edaphotope).
Biostasy: A term that was applied by Erhart in 1956 to periods of soil formation, with rhexistasy referring to phases of denudation. In periods of biostasy there is normal vegetation, while in phases of rhexistasy tere is dying out or lack of vegetation as a result of soil erosion resulting from climatic changes, tectonic displacement, etc.

Biota: The entire complement of species of organisms, plants and animals, found within a given region.

Biotope: The habitat of a   community, or a micro-habitat with a biocoenosis. In the first sense the word as synonymous with ecotope’ the effective physical environment of a biocenosis or biotic community. In the second sense it refers to a small, relatively uniform habitat within the more complex community, e.g. although a forest community occupies its own habitat, each layer of stratum within the forest  may be regarded as a separate biotope (see also niche).

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