Ecology Definition (Ecosystem Perspective)

The word ecology (ecosystem) is derived from the Greek root oikos, which means “household”. The ecosystem is indeed a study of the household of life. It is a holistic (broad-based and integrative) approach to understanding living things in context. As they relate both to their physical environment (abiotic aspects) and to each other (biotic aspects). It is these interactions of living things that provide the raw material for ecological studies. Ecologists also tend to support appropriate responsible social actions to ensure that life in its diversity and richness of connections will continue.


Background of Ecology

The Ecological Society of America has set up an office in Washington, D.C., to provide information that may affect legislative decisions on the environment. Professor E. O. Wilson of Harvard University is leading a campaign to save the tropical rain forests of the world. Ecologists often serve as expert witnesses in legal procedures dealing with the environment.

Ecological Society of America

Anatomy of An Ecosystem

The ecological unit is the ecosystem.

Ecosystem Definition

It is a group of diverse interacting populations found within the regional limits of a neighborhood.

Habitat Definition

This neighborhood (habitat) might be as small as a local pond or as broad as the vast Sahara Desert.

Community Definition

Various interacting populations within an ecosystem make up the community, the living components of the ecosystem.

Explanation of Ecosystem

Some ecologists focus almost exclusively on the living organisms of an ecosystem. While others study the way in which the physical characteristics of the neighborhood constrain and regulate the ecosystem. Although ecosystems vary from tidal pools and barrier reefs to arid stretches of scrub grass. They all share features that have been discovered as ecology. Once an almost completely descriptive branch of biology moved in an increasingly experimental direction.


Features of Ecosystem

These features are.

  1. Energy flow.
  2. Nutrient cycling.
  3. Regulation of population size (numbers of individuals).

Energy Flow in Ecosystem

Energy moves through the community of an ecosystem in a single direction means of a food chain (web). Food web consists of the eaters, the eaten, and a combination of both. Populations are assigned an “occupational” role in an ecosystem in terms of their relation to the overall flow of this energy (food) in the food chain.


The first group in a food chain, usually consisting of green plants. They convert some of the energy of the sun (through photosynthesis) into organic molecules. They use and store in their tissues.



Animals that feed on green plants and each other.

Primary consumers

Primary consumers are herbivores, which subsist on the primary producing plants.

Primary consumers

Secondary consumers

Secondary consumers feed on primary consumers. While tertiary, quaternary, etc., consumers are further along the chain.

secondary consumers


Bacteria, fungi, plants, or animals that feed on dead organisms. And release the bound organic material of the organisms to the food chain.

Decomposers Example

A deer dying in a meadow may be picked apart scavenger species such as vultures or crows. Material not eaten undergoes decay bacteria and fungi. So that inaccessible portions of the corpse not consumed are made available to other organisms in the community.


What is a niche?

Niche Definition

A niche is an occupational or functional slot within an ecosystem that is generally filled a species.


Since energy flow is so vital to the maintenance of an ecosystem. Therefore, the niche is usually categorized in terms of a relation to the food chain. Thus, every ecosystem has a niche for a primary consumer. Usually, herbivore that feeds on a primary producer and is, in turn, eaten a secondary consumer. Niches have been likened to an organism’s caloric profession. These are often defined in more specific ways than the broad category of producer, consumer, etc.


Nutrient Cycling in Ecosystem

As energy in a food chain is passed along from one link to another. Its useful capacity for work is diminished in accordance with the second law of thermodynamics. Heat is given off with every transformation. At the end of the food chain little or no free energy is left, so that recycling is not possible. On the other hand, the matter is not lost as it passes from one component of the food chain to another.

Nutrient Cycling

The passage of organic molecules and their elemental units along the food chain may be described in terms of a cycle. Generally, ecologists follow specific atoms through the cycle, e.g., carbon (C), nitrogen (N), and sulfur (S). Chart their fates as they pass through the food chain, into the environment, and back again into the community. The nitrogen and carbon cycles are particularly well documented.

Carbon Cycle in Ecosystem

The carbon cycle is powered alternately the reduction (through photosynthesis) and the oxidation of carbon. Carbon enters the cycle as atmospheric CO2. CO2 is converted plants to food during photosynthesis. Ultimately, this carbon is converted back to C02 through either respiration or combustion, and the cycle begins again.

Carbon cycle

Regulation of Population Size in Ecosystem

As Malthus and Darwin well knew, natural populations tend to increase exponentially. Rather than incrementally addition of a constant amount. Because of their high reproductive potential. Such populations tend to double, then double again, and so on. A constant rate (reproductive potential) produces dramatic increases over time because as the population increases. The rate is being multiplied an ever-increasing base value (the number of individuals in the population).


Differential Equation to Calculate Population in Ecosystem

The situation is summed up in the differential equation dN/dt = rN. Where N is the number of individuals, t is time, and r is the intrinsic rate of increase. The left side of the equation, the change in a number of individuals over time, is the rate of growth. This rate is equal to the intrinsic rate of increase r multiplied the numbers present. Since each individual share is the tendency to increase in numbers.

Exponential Growth Curve Represents Population in Ecosystem

Such a situation produces the typical exponential growth curve seen in Figure. Growth increases slowly at first. Then rapidly as the steady rate is applied to increasing numbers of individuals. The slope may even approach a vertical line. But such a depiction is only hypothetical. since a population that increases in size at such a great rate will be subject to limiting constraints. Its birthrate will soon be matched or even overtaken an increase in its death rate. Which will tend to maintain the population at a steady number.

Exponentional Growth Curve

Calculation of Stable Population Size in Ecosystem

Stable population size is usually characterized a modification of the previous equation as follows.

dN/dt = rN[{K – N)/K

Where K is the carrying capacity or the maximum number of individuals a habitat can support. Here the rate of growth is modified a factor (K – N)/K. As seen in Figure, an early period of slow growth, the lag phase, is followed a very marked period of growth, the exponential {log) phase. This then gives way to a long-term period of stability of numbers, the plateau phase.

Stable Population Size

Some variation may occur in this third phase, including overshoot, oscillation about a mean. However, stability at a lower number of individuals, or even a crash in the population leading to extinction.

Maintaining Population in Ecosystem

Mechanisms for maintaining uniform population size are of two types.

Density-dependent mechanisms

Which are sensitive to the size of the population and increase in effectiveness as population size increases.

Density-independent mechanisms

Which operate independently of population size and exert similar destructive effects on crowded or sparse populations.

The control of population size is one of several areas in which evolution and ecology coincide. Field experimentation in a variety of habitats has enabled ecologists to sharpen our understanding of the mechanisms of natural selection.

Types of Ecosystems

Biosphere Definition

In one sense, the relatively thin shell of ocean, land, air, and freshwater that makes up the arena for all life on earth is a single ecosystem called the biosphere. The concept of spaceship earth emphasizes the interactive unity of all living things on the planet. Within the biosphere, an older traditional subdivision of major ecological types has been established. Land regions have been more intensively probed than marine or fresh aquatic habitats. But this does not reflect assigned importance or even intrinsic interest or complexity.

Biome Definition

A biome is any of several unique terrestrial ecosystem types. The biomes constitute the largest community units classified ecologists. The significant biomes of the earth are as follows.

Tropical Rain Forest Ecosystem

Dense forest tracts characterized warm temperatures and very heavy rainfalls. Trees are abundant, but the apparent fertility is deceiving. Since the soils are actually of poor quality.

Tropical Rain Forest

Desert Ecosystem

Areas of extremely scanty rainfall and only modest plant life. Although the sandy Sahara is the best known of the deserts. Many desert regions are rocky and different from popular conceptions.


Chaparral Ecosystem

Regions in which there are prolonged, hot, dry summers and temperate rainy winters. In which the dominant vegetation forms are small trees and shrubs. The animals are usually small with bland coloration.


Savannas Ecosystem

Grassland regions in the tropics characterized light and seasonal rain. The grasslands of Africa, which begin below the desert. These are dominated deep-rooted grasses with very few patches of shrubs and trees. In this ideal grazing region, a rich diversity of large mammals (giraffes, zebras, wildebeests, etc.) dominates the ecosystem.


Temperate Grasslands Ecosystem

Large tracts of land in temperate zones characterized limited water availability during much of the year. Clumps of scrub grass, shrubs, and some annual plants predominate. Small rodents coexist with large carnivores, which are dependent on the smaller mammals.

Temperate Grasslands

Taiga Ecosystem

Northern forests thick with massive cone-bearing evergreen trees. Animal life includes smaller animals such as hares, mice, shrews, and lynxes. Larger ones, such as bears, elks, deer, and moose. Snow is present most of the year.


Tundra Ecosystem

A modified grassland region of upper northern areas. It is so cold that a permanent layer of frozen undersoil (permafrost) exists. A short growing season during the northern summer provides sustenance for shrubs and rushes and for animal life (fauna). Which includes multitudinous insects, birds, lemmings, and foxes.


Temperate Deciduous Forest Ecosystem

Rich stands of trees that shed their leaves during the cold season, bushes and shrubs, and grasses interspersed with cryptogamic plants. Cold winters alternate with warm summers of adequate rainfall. Animal life is abundant, ranging from mice, chipmunks, and raccoons to wolves and mountain lions.

Temperate Deciduous Forest

Water Ecosystem

Most of our planet’s surface consists of water. The marine (saltwater) environment makes up about 70 percent of that surface. Both freshwater and marine environments possess a rich array of community life and significantly affect the economic aspects of human societies.

water ecosystem

Ocean Ecosystem

From an ecological perspective, the oceans can be divided into a neritic region above the continental shelf. The oceanic depths beyond the relatively shallow shelf (see Figure). The portion of the neritic region just offshore is named the littoral zone. Because of its currents and complete penetration the sun due to its shallowness. It is particularly rich in plant and animal life. Shoreward of the littoral zone, an intertidal zone is periodically covered with water at high tide and exposed at low tide. The ocean depths are divided into a pelagic zone, rich in plankton, and the even deeper assal zone.

Ocean Ecosystem

Stability of Ecosystem

Some ecologists have described ecosystems as supra-organisms possessing inherent properties of growth, metabolism, periodicity in activities, and eventually death. Since ecosystems are far more open and less firmly bounded than individual organisms. Such a view may be an oversimplification of the actual case. But it is useful in classifying some aspects of ecosystem function. The interdependent relationships obtaining within a community are described as the web of life. It is reflecting the complexity of interactions that occur.


The food chains that exist within communities are complex networks. In which many different species may play the role of producer or consumer or decomposer. In a forest in the United States, up to 60 different species of birds might feed upon many hundreds of species of insects. All these birds are part of a single trophic level. They get their food in the same way and bear a similar nutritional relationship to other members of the food chain.

Stability of Ecosystem

Stability of ecosystems was once equated with complexity, particularly the complex interactions occurring within a food web. More recent field studies, however, show that some simple ecosystems may possess considerable durability. However, if only one population exists at a level. The loss of that population may doom the entire ecosystem. Although ecosystems demonstrate some flexibility and tend to maintain their integrity.

Factors Affecting the Stability of Ecosystem

They may be irreparably harmed the following factors.

  1. Sudden shifts in the environment (temperature change, drought, flooding) that destroy a significant portion of the community.
  2. Uncontrolled increase in the numbers of populations due to failure of the mechanisms for population control.
  3. Loss of key minerals or other nutrients in the ecosystem.
  4. Human interference, which may lead to the destruction of habitats, an overkilling of specific species.
  5. Pollution with toxic materials that cannot be handled within the ecosystem.
Factors Affecting Stability of Ecosystem

Ecological Succession in Ecosystem

Just as individuals undergo change as they mature. So, ecosystems evolve new characteristics and gradually supplant older communities with new populations. This slow change in the makeup of the community within a habitat is called succession. Succession often occurs as older inhabitants modify their environments to provide new opportunities. Succession continues until a climax community is formed. One that is extremely well suited to the environment and remains essentially unchanged through long periods of time.


Biomass and Species Dispersal in Ecosystem

Definition of Biomass

It refers to the weight of living organisms within an ecosystem. It is often applied to trophic levels to provide an insight into what transpires during the passage of energy along a food chain. Because of the continual loss of biomass in proceeding along a food chain the community can be considered a pyramid (see Figure). In a food (energy) pyramid a broad producer base is topped ever-diminishing populations of consumers. The terminal consumer forms the apex of the pyramid. Energy transfer in a typical food pyramid, starting with 1 million kcal of sunlight.

Biomass pyramid

Carrying Capacity of Ecosystem

The carrying capacity of a habitat refers to the upper limit of life-support capabilities of that habitat. It is usually expressed in terms of numbers of individuals that can survive within a stable community. For animals, the carrying capacity is generally a function of available food resources. While for plants it may be mineral nutrients, C02 levels, or the availability of sunlight. When the carrying capacities are relatively high, population densities tend to be large. When the carrying capacities are low, populations tend to be sparse. A particularly high carrying capacity for many species of both plants and animals is characteristic of a tropical rain forest.

Carrying Capacity of Ecosystem

Population Density of Ecosystem

Population density is a quantitative feature of ecosystems. Its qualitative aspect is the dispersal of individuals in space. Eugene P. Odum of the University of Georgia has cited three broad distribution patterns.

Random distribution

The distribution in which individuals are scattered without pattern throughout the habitat.

Uniform distribution

Distribution in which regular patterns of dispersal occur, such as flowers in a flower bed.


In which irregular groupings are discerned, such as flocks of wild birds.

Patterns of dispersal are influenced degrees of socialization in a population. The nature of the terrain and the arrangement of its plant life. Further, interactions with other species, availability of resources, and so forth. Dispersive factors tend to scatter members of a population. Whereas cohesive factors tend to bring individuals together.

Population Density and Distribution

Upsetting the Stability of An Ecosystem (World War 1)

Ecosystems possess resiliency and resist a variety of perturbations in a manner suggesting the operation of homeostatic control mechanisms. Slow changes over time tend to lead through a series of successions to the relatively long-term stability of a climax community. Environmental catastrophes can plunge even a stable climax community into chaos. But many less dramatic disturbances can be borne. Younger communities, which are far more active and productive than more mature systems. They are less able to resist environmental insult.

Example of World War 1

By the time of World War 1 ecologists had demonstrated that because of competition no two species can occupy the same niche for very long. This phenomenon is called niche rule. In the 1930s in an elaborate series of experiments with Paramecium a Russian biologist, G. F. Gause.

Competitive Exclusion Principle

He expanded this rule showing that in competing for a scarce resource one species tends to drive out a competing species. This competitive exclusion principle, or Gause’s principle. This principle has been extensively confirmed in a variety of laboratory experiments. Further, has stressed the role of competition in determining species survival within the ecosystem. However, the 1980s ecologists became aware of the possibility of species occupying the same niche and surviving together in nature. At the present time, competitive exclusion is believed to operate but is still being evaluated.

Simplification and Shrinkage of Niches in Ecosystem

A great diversity of species and intricate pattern of interactions among the communities were once thought to confer greater stability on an ecosystem. Computer simulations of hypothetical ecosystems have challenged this traditional view. Simpler ecosystems with fewer branches in their functional food webs demonstrate a greater apparent degradation to environ­mental assaults. However, they tend to recover rather rapidly and assume new stable arrangements. Complex ecosystems are not markedly disrupted at first dislocations in the physical environment. But long-term reverberations are set up that may eventually lead to permanent disruption.

Positive Effect

A clearer positive effect of the diversity of the physical environment on community stability is observed. Where several influences converge to influence temperature, rainfall, wind velocities, and direction. Ecosystems seem better able to adjust to temporary dislocations. Human intervention generally simplifies all aspects of an ecosystem. Where a variety of species at separate trophic levels exist in nature. Moreover, the introduction of agriculture or the setting up of a village reduces these species to one or even none.


As a result of monoculture organization, many farmers clear a field and plant a single crop. Should disease strike that corn crop the entire “artificial” ecosystem would crash. Since the corn is the primary producer here. The use of highly inbred strains of staples increases the vulnerability of these crops to natural enemies. It represents a source of great vulnerability for both the ecosystem and the farmer.


Pollution in the Ecosystem

Population Definition

Pollution is generally defined as the introduction of harmful materials to an ecosystem. Although pollution has been regarded as a human activity in which plastics, synthetic toxins, non-decomposing chemicals. Pollutants are brought into the flow channels of the ecosystem. It may also involve natural processes that produce materials that cause ecosystems to “belch,” “vomit,” or even die. Volcanoes and forest fires spew noxious ash and other atmospheric pollutants that can seriously damage or even destroy ecosystems.

Problem with Population Due to Pollution

One problem with pollutants is that they become more concentrated as they move along a food chain. A lake may contain only moderate levels of the pesticide DDT. But the tiny invertebrates in that lake may concentrate the pesticide 100 times. However, still greater concentrations are accumulated and stored in the fatty tissue of the fish that feed on the small invertebrates. By the time the DDT reaches the birds that feed on the fish. Its levels are many thousands of times greater than in the lake.


Pollution and Ecosystem

Pollution of ecosystems elemental metals such as lead and mercury has been well documented. These substances have been particularly devastating to higher-level predators. These include not only large wild carnivores but human beings as well.

Lead Pollution and Its Effect on Ecosystem

Lead belongs to the class of heavy metals that tend to interact with and precipitate protein. Tissues like the brain and cells like erythrocytes are particularly sensitive to the effects of lead. Among the symptoms of lead, poisoning is weakness and muscle tremors. Furthermore, its interference with thought processes, impaired transport of oxygen erythrocytes, and nerve destruction. Lead moves into communities through its presence in gasoline.

Lead Pollution

Combustion of leaded gasoline tends to spew compounds of lead into the atmosphere. Most cars manufactured today are required to use lead-free gasoline, and the atmospheric contamination lead has considerably abated. At one time lead-based paints were used extensively. However, these are no longer manufactured. Children chewing on paint in old apartments and homes may contract lead poisoning.

Lead pollution

Mercury Pollution and Its Effect on Ecosystem

Mercury has also drawn the interest of historians. Mercury salts used hatters in France to soften their felts were believed to have caused some nerve damage. Many hatters supposedly were irritable and symptoms of the nervous disorder as a result of slow mercury poisoning. The image of the mad hatter, a character in Alice in Wonderland, springs from that historical perception. Some skeptics have challenged the authenticity of such reports in recent years. However, mercury salts from industrial wastes in Minamata Bay (Japan) have been shown to have killed many citizens who ate contaminated shellfish.

Eutrophication Affecting Ecosystem

Eutrophication involves too much of a good thing. An overabundance of nutrients is provided in the waters of a river or lake. It is stimulating an overgrowth of phytoplankton or algae. This floral population soon reaches a density at which vital gases and nutrients are used up. The overgrown “blooms” produce toxins and die as an unpleasant rotting mass. Eutrophication, although rooted in the concept of excessive nutrient levels. It may also be caused a rise in water temperature.


However, usually due to the dumping of hot effluents factories. The increased temperature may speed up activity within the algal community and produce overgrowth. The result is the same as that brought on an excess of nutrients. Eutrophication may also involve the overgrowth of larger plants such as weeds or water lilies. In lakes used for recreational purposes, such overgrowth of weeds may cause economic hardship to those dependent on tourists or summer residents for their livelihood.

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