Chapter 3

ECOSYSTEMS

What is an ecosystem?

An ecosystem is a self-sustained community of plants and animals

existing in its own environment.

The term ecosystem may be defined as a system resulting from the

integration of all the living and non living factors of the environment.

Desert, Forest, Ocean, Grasslands, Mountains, etc. are all ecosystems.

Biome and Biosphere

A Biome is a collection of related ecosystems. The sum

total of all the ecosystems on planet earth is called the

biosphere, which includes all the earth’s living

organisms interacting with the physical environment

as a whole to maintain a steady state ecosystem.

Ecology and Ecosystem

The two terms are commonly used together but there is a

difference between them.

Ecosystem is the basic and functional unit of ecology.

Ecology is the branch of science that studies the

interrelationships between the living organisms with their

environment.

Classification of Ecosystems

Natural Ecosystems and Man Made/Artificial Ecosystems

Natural Ecosystems Ecosystems which are the gifts of nature are called

natural ecosystems. Deserts, forests, oceans,

grasslands, etc. are natural ecosystems .

Man Made/Artificial Ecosystems

Ecosystems which are engineered by man are called

Man Made or artificial ecosystems. Examples :

Gardens, Man made lakes, agricultural fields, etc.

Natural Ecosystem Artificial Ecosystem(i) Plants of one species are often scattered (i) Plants of the small species grow

in close proximity

(ii) Natural ecosystems usually have alternate sources of food available if one fails.

(ii) Artificial ecosystems usually contain less food choices.

(iii) Natural ecosystem is developed under natural conditions.

(iii) Artificial ecosystem is created and manipulated by human activities.

(iv) In a natural ecosystem the inorganic nutrients are returned to the soil from which they were taken.

(iv) In artificial ecosystems, the inorganic nutrients do not return to the soil but are carried away at some other places.

(v) Natural ecosystems have no distinct boundaries.

(v) Artificial ecosystems have distinct boundaries.

Natural Vs Artificial Ecosystems

Structure of Ecosystems All ecosystems whether natural or man made consist of the following two components

Abiotic Components (Non living Abiotic Components (Non living Components )Components )

Biotic Components (Living Components)

A comparative account of different ecosystemsType of ecosystem Abiotic Factors Biotic Factors

Grassland Ecosystem Inorganic elements like C, H, N along with climatic components like temperature, rainfall, light, etc

Main producers are grasses along with the presence of different levels of consumers

Desert Ecosystem Low rainfall, high temperature and sandy soil are the main features

Cactus, Opuntia, etc thorny plants are present. Consumers include insects, reptiles, snakes, rodents, etc.

Forest Ecosystem Inorganic and organic substances found in soil and the climatic factors like rainfall, temperature, wind, etc.

Producers comprise of different kinds of trees, shrubs, etc. Consumers have a wide range with representations from primary secondary and tertiary consumers like deer, elephant, tiger,etc.

Pond Ecosystem Atmospheric gases are dissolved in water, minerals are also found in dissolved state

Submerged, emergent aquatic plants are present. Small fishes, beetles, mollusca, are also found

Marine Ecosystem Light, temperature, pressure, salinity constitute the main abiotic factors

Phytoplanktons like diatoms, microscopic algae, crustaceans, carnivorous fishes, etc are found

Functions of Ecosystems

The key functional aspects of the ecosystem are:

(1)Food Chain and Food Web

(2)Energy Flow

(3)Nutrient cycling

(4) Development and stabilization

Food Chain

The process of eating and being eaten

Grazing and Detritus Food Chain

Detritus Food Chain

Grazing Food Chain

Food web Intermixing of food chains

Energy Flow in Ecosystems

First Law of Thermodynamics energy can neither be created nor destroyed but only is

transformed from one form to another.

Second Law of Thermodynamics-The second law of thermodynamics states that no

energy transformations are 100% efficient.

10 Percent Rule of Energy

As a rule of thumb, 90 percent of the energy involved is degraded at each trophic

transfer and only 10 percent of the energy is conserved in the organism's tissue.

Nutrient cycling

The movement, and exchange of organic and inorganic matter

back into the production of living matter.

Carbon Cycle

Carbon is absorbed through three major links in nature: the oceans, the atmosphere and the terrestrial system

Nitrogen Cycle

Nitrogen Fixation

Assimilation

Ammonification

Nitrification

Denitrification

Phosphorus cycleThe phosphorus cycle is a sedimentary cycle and , the atmosphere is not a reservoir for phosphorous nor do microorganisms fix phosphorus as they do nitrogen !!

Ecological Succession

Environment is always kept on changing over a period of time due to

(i)variations in climatic and physiographic factors, and

(ii) the activities of the species of the communities themselves.

Ecological Succession is an orderly sequence of different communities over a period of time.

Types of ecological succession

Primary Succession Secondary Succession

Primary succession is the process by which an area first changes from bare rock into a functioning ecosystem. Secondary succession is the process by which an ecosystem that has been destroyed gradually returns to its previous state.

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Process / Stages of Ecological Succession

Nudation

Invasion

Competition

Stabilization

Homeostasis in ecosystem

Homeostasis is referred to as balance of nature. An

ecosystem maintains a biological equilibrium between the

different components and this property is referred to as

homeostasis.

The ability of a community to establish itself in a different

habitat or area is also a form of ecological resilience.

Ecosystems

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