SCIENCE

Ecosystem

Definition

noun, plural: ecosystems

A system that includes all living organisms (biotic factors) in an area as well as its physical environment(abiotic factors) functioning together as a unit.

Supplement

An ecosystem is made up of plants, animals, microorganisms, soil, rocks, minerals, water sources and the local atmosphere interacting with one another.

Word origin: coined in 1930 by Roy Clapham, to denote the physical and biological components of an environment considered in relation to each other as a unit.
Related phrases: ecosystem model, ecosystem ecology, ecosystem diversity.
See also: biotic factor, abiotic factor, ecology.

Abiotic Components

These include the non-living, physico - chemical factors such as air, water, soil and the basic elements and compounds of the environment.

Abiotic factors are broadly classified under three categories.

Climatic factors which include the climatic regime and physical factors of the environment like light, humidity, atmospheric temperature, wind, etc.

Edaphic factors which are related to the structure and composition of soil including its physical and chemical properties, like soil and its types, soil profile, minerals, organic matter, soil water, soil organisms.

Inorganic substances like water, carbon, sulphur, nitrogen, phosphorus and so on. Organic substances like proteins, lipids, carbohydrates, humic substances etc.

Biotic Components

It comprises the living part of the environment, which includes the association of a number of interrelated populations belonging to different species in a common environment.

The populations are that of animal community, plant community and microbial community.

Biotic community is distinguished into autotrophs, heterotrophs and saprotrophs.

Autotrophs (Gr: auto - self, trophos - feeder) are also called producers, convertors or transducers.

These are photosynthetic plants, generally chlorophyll bearing, which synthesize high-energy complex organic compounds (food) from inorganic raw materials with the help of sunlight, and the process is referred as photosynthesis.

Autortophs form the basis of any biotic system.

In terrestrial ecosystems, the autotrophs are mainly the rooted plants.

In aquatic ecosystems, floating plants called phytoplankton and shallow water rooted plants called macrophytes are the dominant producers.

Heterotrophs (Gr: heteros - other; trophs - feeder) are called consumers, which are generally animals feeding on other organisms.

Consumer's also referred as phagotrophs (phago - to ingest or swallow) or macroconsumers are mainly herbivores and carnivores.

Herbivores are referred as First order consumers or primary consumers, as they feed directly on plants.

For e.g., Terrestrial ecosystem consumers like cattle, deer, rabbit, grass hopper, etc.

Aquatic ecosystem consumers like protozoans, crustaceans, etc.

Carnivores are animals, which feed or prey upon other animals.

Primary carnivores or Second order consumers include the animals which feed on the herbivorous animals.

For e.g., fox, frog, predatory birds, smaller fishes, snakes, etc.

Secondary carnivores or Third order consumers include the animals, which feed on the primary carnivores.

For e.g., wolf, peacock, owl, etc.

Secondary carnivores are preyed upon by some larger carnivores.

Tertiary carnivores or Quaternary consumers include the animals, which feed on the secondary carnivores.

For e.g., lion, tiger, etc.

These are not eaten by any other animals.

The larger carnivores, which cannot be preyed upon further are called top carnivores.

Saprotrophs (Gr: sapros - rotten; trophos - feeder) are also called decomposers or reducers. They break down the complex organic compounds of dead matter (of plants and animals).

Decomposers do not ingest their food. Instead they secrete digestive enzymes into the dead and decaying plant and animal remains to digest the organic material. Enzymes act upon the complex organic compounds of the dead matter.

Decomposers absorb a part of the decomposition products for their own nourishment. The remaining substances are added as minerals to the substratum (mineralisation).

Released minerals are reused (utilised) as nutrients by the plants (producers).

Biotic and Abiotic Factors

Biotic and abiotic factors are interrelated. If one factor is changed or removed, it impacts the availability of other resources within the system.

Biotic FactorsBiotic, meaning of or related to life, are living factors. Plants, animals, fungi, protist and bacteria are all biotic or living factors.

Abiotic Factors
Abiotic, meaning not alive, are nonliving factors that affect living organisms. Environmental factors such habitat (pond, lake, ocean, desert, mountain) or weather such as temperature, cloud cover, rain, snow, hurricanes, etc. are abiotic factors.

A System
Biotic and abiotic factors combine to create a system or more precisely, an ecosystem. An ecosystem is a community of living and nonliving things considered as a unit.

The Impact of Changing Factors
If a single factor is changed, perhaps by pollution or natural phenomenon, the whole system could be altered. For example, humans can alter environments through farming or irrigating. While we usually cannot see what we are doing to various ecosytems, the impact is being felt all over. For example, acid rain in certain regions has resulted in the decline of fish population.

Abiotic and Biotic Factors

Abiotic factors are essentially non-living components that effect the living organisms of the freshwater community.

When an ecosystem is barren and unoccupied, new organisms colonising the environment rely on favourable environmental conditions in the area to allow them to successfully live and reproduce.

These environmental factors are abiotic factors. When a variety of species are present in such an ecosystem, the consequent actions of these species can affect the lives of fellow species in the area, these factors are deemed biotic factors.

This page will go into the abiotic factors of the freshwater environment which determine what sort of life would be suited to living (and adapting) to the conditions of the ecosystem.

As described in previous pages, the light from the sun is a major constituent of a freshwater ecosystem, providing light for the primary producers, plants. There are many factors which can affect the intensity and length of time that the ecosystem is exposed to sunlight;

• Aspect - The angle of incidence at which light strikes the surface of the water. During the day when the sun is high in the sky, more light can be absorbed into the water due to the directness of the light. At sunset, light strikes the water surface more acutely, and less water is absorbed. The aspect of the sun during times of the day will vary depending on the time of the year.
• Cloud Cover - The cloud cover of an area will inevitably affect intensity and length of time that light strikes the water of a freshwater ecosystem. Species of plants rely on a critical period of time where they receive light for photosynthesis.
• Season - The 4 seasons in an ecosystem are very different, and this is because less light and heat is available from the sun in Winter and vice versa for Summer, therefore these varying conditions will affect which organisms are suited to them.
• Location - The extreme latitudes receive 6 months of sunlight and 6 months of darkness, while the equator receives roughly 12 hours of sunlight and darkness each day. This sort of variance greatly affects what type of organisms would occupy freshwater ecosystems due to these differences.
• Altitude - For every one thousand metres above sea level, average temperature drops by one degree Celsius. Altitude will also affect the aspect of which sunlight hits the freshwater ecosystem, therefore playing a part on which organisms will occupy it.

As you can see, many abiotic factors can play a part in determining the end product, which organisms live and succeed in the freshwater ecosystem. The sun provides light for photosynthesis, but also provides heat giving a suitable temperature for organisms to thrive in. The temperature of a freshwater environment can directly affect the environment as a whole and the organisms that occupy it.

Enzymes operate best at an optimum temperature, and any deviation from this temperature 'norm' will result in below optimum respiration in the organism. All aquatic life are ectotherms, meaning their body temperature varies directly with its environments.

Temperature affects the density of substances, and changes in the density of water means more or less resistance for animals who are travelling in the freshwater environment.

The next page will continue to look at how these abiotic factors affect the way in which organisms operate in the freshwater ecosystem. The above examples of abiotic factors involve physical characteristics of the freshwater environment, which are continued, with subsequent information studying how the chemical composition of the freshwater ecosystem also affects which organisms survive in the environment and how they cope in these conditions.