2. 5.1. Definition, History and Concepts of Ecosystem
An ecosystem consists of all the organisms and the physical environment with
which they interact.
These biotic and abiotic components are linked together through nutrient cycles
and energy flows.
Energy enters the system through photosynthesis and is incorporated into plant
tissue.
The term "ecosystem" was first used in 1935 by British ecologist called Tansley.
Ecosystem consists of two words: Eco-Environment, System -Interaction.
American ecologist (Odum) defined- Ecosystem is the basic functional unit of
organism and their environment interacting with each other & with their own
components
He devised the concept as the importance of transfers of materials b/n organisms
and their environment
3. 5.2. Ecosystem Characteristics and Classification
• It is characterized by the presence of living/biotic components (plants, animals,
bacteria, algae and fungi) and non-living/abiotic components (light, shade,
temperature, water, humidity, air, soil, wind and pH).
• Ecosystems are dynamic entities,they are subject to periodic disturbances and are
always in the process of recovering from some past disturbance.
• The tendency of an ecosystem to remain close to its equilibrium state, despite that
disturbance, is termed its resistance.
• The capacity of a system to absorb disturbance and reorganize on undergoing
change to retain the same function, structure, and identity is termed its ecological
resilience.
• Ecosystem classifications are specific ecological classifications that consider all
four elements of the ecosystems: biotic, abiotic, the interactions between and
within them, and the physical space they occupy.
4. There are two big categories of ecosystem: Terrestrial and Aquatic ecosystem
A. Terrestrial Ecosystem:
• Terrestrial ecosystems are exclusively land ecosystems, and they are different
types distributed over the earth spaces.
Forest Ecosystem, Grassland Ecosystem, Tundra Ecosystem, Desert Ecosystem
1. Forest Ecosystem
• A forest ecosystem consists of several plants, particularly trees, animals and
microorganisms that live in coordination with the abiotic factors of the
environment.
• Forests help in maintaining the temperature of the earth and are the major carbon
sink.
2. Grassland Ecosystem
• In GE, the vegetation is dominated by grasses and herbs. Examples are temperate
grasslands and savanna grasslands.
5. 3.Tundra Ecosystem
• Tundra ecosystems are devoid of trees and are found in cold climates or where
rainfall is scarce. These are covered with snow for most of the year.
• Tundra type of ecosystem is found in the Arctic or mountain tops.
4. Desert Ecosystem
• Deserts are found throughout the world. These are regions with little rainfall and
scarce vegetation. The days are hot, and the nights are cold.
B. Aquatic Ecosystem
• Aquatic ecosystems are ecosystems of the water body, which are divided into two
types: Freshwater & Marine Ecosystem
1. Freshwater Ecosystem
• It is an aquatic ecosystem that includes lakes, ponds, rivers, streams and wetlands.
They have no salt content in contrast with the marine ecosystem.
6. 2. Marine Ecosystem
• The marine ecosystem includes seas and oceans. These have a more substantial
salt content and greater biodiversity in comparison to the freshwater ecosystem
5.3. Structure and Functions of Ecosystem
• An ecosystem has two components biotic and abiotic
• The non living constituents include, habitat, gases, solar radiation, temperature,
moisture and inorganic and organic nutrients.
• The living organisms are sub divided into producers, consumers and decomposers.
• Abiotic Components include basic inorganic and organic components of the
environment or habitat of the organism.
• The inorganic components of an ecosystem are co2, water N2, Ca phosphate, all of
which are involved in matter cycle (biogeochemical cycles).
• The organic components are proteins, carbohydrates, lipids and AAs, all of which are
synthesized by the biota of an ecosystem and are reached to ecosystem as their wastes,
dead remains etc.
7. 5.3.2. Functions of Ecosytem
• Ecosystem function is the capacity of natural processes and components to
provide goods and services that satisfy human needs, either directly or indirectly.
• Ecosystem functions are subset of ecological processes and ecosystem structures.
Each function is the result of the natural processes of the total ecological sub-
system of which it is a part.
• Natural processes, in turn, are the result of complex interactions between biotic
and abiotic (chemical and physical) components of ecosystems through the
universal driving forces of matter and energy.
• There are four primary groups of ecosystem functions
1) regulatory functions 2) habitat functions 3) production functions 4) information
functions.
Regulatory functions: It is the capacity of natural ecosystems to regulate essential
ecological processes and life support systems through bio-geochemical cycles.
8. Habitat functions: the ecosystems provides refuge and a reproduction habitat to the
plants and animals, thereby contribute to (in situ) conservation of genetic diversity.
Production functions: Photosynthesis and nutrient uptake by autotrophs converts
energy, Co2 and water into a variety of carbohydrates which are then used by 2o
producers to create even larger variety biomass
Information functions: natural ecosystems contribute to maintenance of human
health by providing opportunities for spiritual enrichment, cognitive development,
recreation and aesthetic experience.
5.4. Productivity in an Ecosystem
The productivity of an ecosystem is the rate at which solar energy is fixed by the
vegetation of the ecosystem
It is classified into 1o productivity, 2o productivity and net productivity.
1o productivity is the rate at which radiant energy is stored by photosynthetic and
chemosynthetic activity of producers;
It is also classified as gross 1o productivity (GPP) and net 1o productivity (NPP)
2o productivity refers to the rates of energy storage at consumer levels.
9. 5.5. Trophic Structures in Ecosystem
• Trophic structure is defined as the partitioning of biomass between trophic
levels (community that uptake energy and nutrients in similar ways),
• The major biological components of ecosystems are the producers/autotrophs
that are self-feeders and the consumers/heterotrophs.
Autotrophs - photosynthesize making their own food from compounds in the
environment (organisms such as green plants and algae).
• A few specialized producers can convert simple compounds to more complex
compounds without sunlight, a process called chemosynthesis.
Heterotrophs (consumers) feed on other organisms or their remains.
• Herbivores feed on plants.
• Carnivores feed on animals.
• Omnivores feed on both plants and animals.
• Detritivores feed on dead organic matter and break down into molecules
• Decomposers (bacteria/fungi) break down organic detritus into simpler molecules
10. 5.6. Energy Flow in Ecosystems
Food chains and food webs
• Help us understand how eaters, the eaten, and the decomposed are interconnected
in an ecosystem.
• The sequence of organisms as they are eaten is a food chain.
• Food webs are complex networks of interconnected food chains. They are maps of
life's interdependence.
Trophic levels are classified in the following feeding levels in ecosystem,
(1) Producers belong to the first trophic level.
(2) Primary consumers belong to the second trophic level.
(3) Secondary consumers belong to the third trophic level.
(4) Detritivores and decomposers process detritus from all trophic levels
11. • Energy flow in a food web/chain decreases at each succeeding organism in a chain
or web. The dry weight of all organic matter within the organisms of a food
chain/web is called biomass.
