Ecosystem Concept

Following are some of the basic concepts in modern ecology:

An ecosystem is defined as a dynamic entity composed of a biological community

and its associated abiotic environment. Often the dynamic interactions that occur

within an ecosystem are numerous and complex. Ecosystems are also always undergoing alterations to their biotic and abiotic components. Some of these alterations begin first with a change in the state of one component of the ecosystem, which then cascades and sometimes amplifies into other components because of relationships.

In recent years, the impact of humans has caused a number of dramatic changes to a variety of ecosystems found on the Earth. Humans use and modify natural ecosystems through agriculture, forestry, recreation, urbanization, and industry. The most obvious impact of humans on ecosystems is the loss of biodiversity. The number of extinctions caused by human domination of ecosystems has been steadily increasing since the start of the Industrial Revolution. The frequency of species extinctions is correlated to the size of human population on the Earth, which is directly related to resource consumption, land-use change, and environmental degradation. Other human impacts to ecosystems include species invasions to new habitats, changes to the abundance and dominance of species in communities, modification of biogeochemical cycles, modification of hydrologic cycling, pollution, and climatic change.

1.1. Major Components of Ecosystems

Ecosystems are composed of a variety of abiotic and biotic components that function in an interrelated fashion. Some of the more important components are: soil,

atmosphere, radiation from the Sun, water, and living organisms.

Soils are much more complex than simple sediments. They contain a mixture of weathered rock fragments, highly altered soil mineral particles, organic matter, and living organisms. Soils provide nutrients, water, a home, and a structural growing medium for organisms. The vegetation found growing on top of a soil is closely linked to this component of an ecosystem through nutrient cycling.

The atmosphere provides organisms found within ecosystems with carbon dioxide for photosynthesis and oxygen for respiration. The processes of evaporation, transpiration, and precipitation cycle water between the atmosphere and the Earth's surface.

Solar radiation is used in ecosystems to heat the atmosphere and to evaporate and

reactions. Plants and animals receive their water from the Earth's surface and soil. The original source of this water is precipitation from the atmosphere.

Ecosystems are composed of a variety of living organisms that can be classified as

producers, consumers, or decomposers. Producers or autotrophs, are

organisms that can manufacture the organic compounds they use as sources of energy and nutrients. Most producers are green plants that can manufacture their

food through the process of photosynthesis. Consumers or heterotrophs get their

energy and nutrients by feeding directly or indirectly on producers. We can distinguish two main types of consumers. Herbivores are consumers that eat plants

for their energy and nutrients. Organisms that feed on herbivores are called

carnivores. Carnivores can also consume other carnivores. Plants and animals

supply organic matter to the soil system through shed tissues and death. Consumer organisms that feed on this organic matter, or detritus, are known as detritivores or decomposers. The organic matter that is consumed by the detritivores is eventually

converted back into inorganic nutrients in the soil. These nutrients can then be used

by plants for the production of organic compounds.

The following graphical model describes the major ecosystem components and their interrelationships (Fig).

Figure : Relationships within an ecosystem. 1.2. Energy and Matter Flow in Ecosystems

Many of the most important relationships between living organisms and the environment are controlled ultimately by the amount of available incoming energy received at the Earth's surface from the Sun. It is this energy, which helps to drive biotic systems. The Sun's energy allows plants to convert inorganic chemicals into organic compounds.

Only a very small proportion of the sunlight received at the Earth's surface is transformed into biochemical form. Several studies have been carried out to

of the available solar insolation. Most ecosystems fix less than 1% of the sunlight available for photosynthesis.

Living organisms can use energy in basically two forms: radiant or fixed. Radiant

energy exists in the form of electromagnetic energy, such as light. Fixed energy is

the potential chemical energy found in organic substances. This energy can be released through respiration. Organisms that can take energy from inorganic sources and fix it into energy rich organic molecules are called autotrophs. If this energy comes from light then these organisms are called photosynthetic autotrophs. In most ecosystems plants are the dominant photosynthetic autotroph.

Organisms that require fixed energy found in organic molecules for their survival are called heterotrophs. Heterotrophs who obtain their energy from living organisms are called consumers. Consumers can be of two basic types: Consumer and decomposers. Consumers that consume plants are known as herbivores. Carnivores are consumers who eat herbivores or other carnivores. Decomposers or detritivores are heterotrophs that obtain their energy either from dead organisms or from organic compounds dispersed in the environment.

Once fixed by plants, organic energy can move within the ecosystem through the consumption of living or dead organic matter. Upon decomposition the chemicals that were once organized into organic compounds are returned to their inorganic form and can be taken up by plants once again. Organic energy can also move from one ecosystem to another by a variety of processes. These processes include: animal migration, animal harvesting, plant harvesting, plant dispersal of seeds, leaching, and erosion. The following diagram models the various inputs and outputs of energy and matter in a typical ecosystem (Figure ).

ecosystem is changing. To determine both structural and functional changes over time, ecoservices can be estimated.

1.4. Ecoservices represent the goods and services that an ecosystem provides.

Measurements of changes in the soil, water, phytomass and biodiversity of an ecosystem can be used to assess changes in the level and type of ecoservices that ecosystem provides.

Although a wide range of ecosystem functions and their associated goods and services have been referred to in literature, our experience suggests that it is convenient to group ecosystem functions into four primary categories (De Groot et

al, 2000):

(1) Regulation functions: this group of functions relates to the capacity of natural and seminatural ecosystems to regulate essential ecological processes and life support systems through bio-geochemical cycles and other biospheric processes. In addition to maintaining ecosystem (and biosphere) health, these regulation functions provide many services, which have direct and indirect benefits to humans (such as clean air, water and soil, and biological control services).

(2) Habitat functions: natural ecosystems provide refuge and reproduction-habitat to wild plants and animals and thereby contribute to the (in situ) conservation of biological and genetic diversity and evolutionary processes.

(3) Production functions: Photosynthesis and nutrient uptake by autotrophs converts energy, carbon dioxide, water and nutrients into a wide variety of carbohydrate structures which are then used by secondary producers to create an even larger variety of living biomass. This broad diversity in carbohydrate structures provides many ecosystem goods for human consumption , ranging from food and raw materials to energy resources and genetic material.

(4) Information functions: because most of human evolution took place within the context of undomesticated habitat, natural ecosystems provide an essential ‘reference function’ and contribute to the maintenance of human health by providing opportunities for reflection, spiritual enrichment, cognitive development, re-creation and aesthetic experience.

1.5. Succession is a concept that describes directional (not cyclical) changes in

structure and function over time. The types of communities of plants and animals that inhabit an ecosystem fundamentally change it, resulting in changes in the communities themselves. In other words, certain hardy grass species may thrive in nitrogen poor soils, but as they thrive and die, they enrich the soil with more nitrogen. Soil with more nitrogen is no longer suitable for these hardy species, but a range of other grasses and shrubs may then take root and result in new vegetative communities flourishing in the area.

1.6. Ecorestoration: Succession occurs naturally but outside stressors

(disturbances) such as overgrazing, deforestation or invasive species can change derail this process. To put the natural system back on track, ecorestoration techniques can be employed. An ecomonitoring program needs to incorporate protocol (methods) for measuring certain ecosystem parameters (indicators) that will