LIFE ON THE EARTH : ECOLOGY, ECOSYSTEM AND BIOGEOCHEMICAL CYCLES

Introduction

The Earth consists of three major environmental realms:

• Lithosphere
• Atmosphere
• Hydrosphere

Living organisms interact continuously with these realms and together constitute the biosphere. The biosphere includes:

• plants,
• animals,
• microorganisms,
• and all living organisms on Earth.

These organisms interact with environmental components such as:

• land,
• water,
• air,
• soil,
• temperature,
• rainfall,
• sunlight,
• and moisture.

These interactions are essential for the growth, development and evolution of life on Earth.

ECOLOGY

The term ecology is derived from the Greek words:

• ‘Oikos’ meaning ‘house’
• ‘Logy’ meaning ‘study of’

Thus, ecology literally means the study of Earth as a household of living organisms.The term ‘oekologie’ was first used in 1869 by the German zoologist:

• Ernst Haeckel

Definition of Ecology

Ecology is the scientific study of:

• interactions among organisms,
• interactions between organisms and their physical environment.

The environment consists of:

Ecology studies how balance is maintained between these components.

ECOLOGICAL SYSTEM

The interaction of organisms with abiotic factors within a habitat resulting in:

• energy flows,
• and material cycles

is known as an ecological system.Life exists almost everywhere on Earth:

• from poles to equator,
• from sea bottom to atmosphere,
• from deserts to freezing regions,
• and even underground.

HABITAT

A habitat is the totality of physical and chemical factors constituting the environment of organisms.

ECOSYSTEM

A system consisting of:

• biotic components,
• and abiotic components

is known as an ecosystem.All ecosystem components are interrelated and interact continuously.Different ecosystems develop under varying environmental conditions through the process of:

• ecological adaptation

TYPES OF ECOSYSTEMS

Ecosystems are broadly divided into:

1. Terrestrial ecosystems
2. Aquatic ecosystems

TERRESTRIAL ECOSYSTEMS

Terrestrial ecosystems are further classified into biomes.

Biome

A biome is a large plant and animal community occupying a vast geographical area.Biomes are mainly determined by:

• climate,
• rainfall,
• temperature,
• humidity,
• and soil conditions.

Major Terrestrial Biomes

• Forest biome
• Grassland biome
• Desert biome
• Tundra biome

AQUATIC ECOSYSTEMS

Aquatic ecosystems are classified into:

STRUCTURE OF ECOSYSTEM

The structure of an ecosystem includes both:

• abiotic factors,
• biotic factors.

ABIOTIC FACTORS

Abiotic factors include:

• rainfall,
• temperature,
• sunlight,
• humidity,
• soil conditions,
• carbon dioxide,
• water,
• nitrogen,
• calcium,
• phosphorus,
• potassium.

BIOTIC FACTORS

Biotic factors include:

1. Producers
2. Consumers
3. Decomposers

PRODUCERS

Producers include all green plants which prepare food through:

• photosynthesis

CONSUMERS

Primary Consumers

These are herbivorous animals such as:

• deer,
• goats,
• mice.

Secondary Consumers

These include carnivorous animals such as:

• snakes,
• lions,
• tigers.

Tertiary Consumers / Top Carnivores

Carnivores feeding on other carnivores are called top carnivores.Examples:

• hawks,
• mongooses.

DECOMPOSERS

Decomposers feed on dead organisms.Examples:

• vultures,
• crows,
• bacteria,
• microorganisms.

They break down dead matter into nutrients and salts necessary for soil fertility.

FOOD CHAIN

A food chain is the sequence of eating and being eaten through which energy passes from one level to another.

Example of Food Chain

FLOW OF ENERGY

Transfer of energy from one trophic level to another in a food chain is called:

• flow of energy

Energy is lost at every level through:

• respiration,
• excretion,
• decomposition.

Food chains generally contain:

• 3 to 5 trophic levels.

FOOD WEB

Food chains are interconnected with one another forming a:

• food web

In a food web:

• one organism may feed on multiple organisms,
• and may itself be eaten by multiple consumers.

TYPES OF FOOD CHAINS

Grazing Food Chain

• Begins with green plants.
• Herbivores occupy intermediate levels.
• Carnivores occur at higher levels.

Detritus Food Chain

Based on:

• decomposition of dead organic matter,
• and organic wastes.

TYPES OF BIOMES

There are five major biomes:

1. Forest biome
2. Desert biome
3. Grassland biome
4. Aquatic biome
5. Altitudinal biome

FOREST BIOME

Types

Tropical Forests

Equatorial Forests

Characteristics:

• Temperature: 20–25°C
• Evenly distributed rainfall
• Multi-layered tall trees

Tropical Deciduous Forests

Characteristics:

• Seasonal rainfall
• Rich biodiversity
• Medium height trees

Temperate Forests

Characteristics:

• Well-defined seasons
• Broad-leaved trees such as:
  • oak,
  • maple,
  • beech.

Boreal Forests

Characteristics:

• Long cold winters
• Coniferous trees:
  • pine,
  • fir,
  • spruce.

DESERT BIOME

Types

• Hot and dry desert
• Semi-arid desert
• Coastal desert
• Cold desert

Characteristics:

• Rainfall less than 50 mm
• Sparse vegetation
• Few large mammals

GRASSLAND BIOME

Tropical Grasslands (Savanna)

Found in:

• Africa,
• Australia,
• South America,
• India.

Characteristics:

• Grasses dominate
• Trees absent or sparse

Animals:

• zebras,
• giraffes,
• elephants,
• buffaloes.

Temperate Grasslands (Steppe)

Characteristics:

• Hot summers,
• cold winters,
• moderate rainfall.

AQUATIC BIOME

Freshwater Ecosystem

Includes:

• lakes,
• rivers,
• streams,
• wetlands.

Marine Ecosystem

Includes:

• oceans,
• lagoons,
• coral reefs,
• estuaries.

ALTITUDINAL BIOME

Found along mountain slopes such as:

• Himalayas,
• Andes,
• Rockies.

Vegetation changes with altitude.

BIOGEOCHEMICAL CYCLES

Biogeochemical cycles involve cyclic movement of chemical elements between:

• organisms,
• atmosphere,
• water,
• rocks,
• soil.

These cycles are powered mainly by:

• solar energy.

TYPES OF BIOGEOCHEMICAL CYCLES

WATER CYCLE

The circulation of water among:

• atmosphere,
• hydrosphere,
• lithosphere,
• and organisms

in solid, liquid and gaseous forms is called the:

• water cycle or hydrological cycle.

CARBON CYCLE

Carbon is the basic component of organic compounds.The carbon cycle mainly involves conversion of:

• carbon dioxide into organic compounds through photosynthesis.

Process

• Plants absorb carbon dioxide.
• Photosynthesis forms carbohydrates.
• Herbivores consume plants.
• Respiration releases carbon dioxide.
• Decomposition returns carbon dioxide to atmosphere.

OXYGEN CYCLE

Oxygen is the major by-product of photosynthesis.It is involved in:

• oxidation,
• respiration,
• energy release.

Oxygen combines with various elements to form:

• nitrates,
• oxides,
• minerals.

Most oxygen is released through:

• photosynthesis,
• transpiration,
• respiration.

NITROGEN CYCLE

Nitrogen forms about:

• 78% of atmospheric gases

It is essential for:

• proteins,
• amino acids,
• vitamins,
• nucleic acids.

Nitrogen Fixation

Nitrogen becomes usable after fixation through:

• soil bacteria,
• blue-green algae,
• lightning,
• cosmic radiation.

Nitrogen Cycle Process

• Atmospheric nitrogen is fixed.
• Green plants absorb it.
• Herbivores consume plants.
• Decomposition converts nitrogenous wastes into nitrites and nitrates.
• Denitrification converts nitrates back into free nitrogen.

OTHER MINERAL CYCLES

Important minerals include:

• phosphorus,
• sulphur,
• calcium,
• potassium.

These minerals originate from:

• weathering of rocks.

They move through:

• soil,
• water,
• plants,
• animals,
• decomposition.

ECOLOGICAL BALANCE

Ecological balance is a state of:

• dynamic equilibrium within an ecosystem.

It is maintained when species diversity remains relatively stable.

Mechanism of Ecological Balance

Balance is maintained through:

• competition,
• cooperation,
• predator-prey relationships.

Example:

• Herbivores increase in grasslands.
• Carnivores control herbivore population.

ECOLOGICAL SUCCESSION

Disturbance in native vegetation leads to replacement by other species.Example:

• forest clearing may lead to grasses or bamboo replacing forests.

This gradual replacement is called:

• succession

CAUSES OF ECOLOGICAL IMBALANCE

Ecological balance may be disturbed due to:

• introduction of new species,
• natural hazards,
• human interference.

Human activities have caused:

• ecosystem disturbances,
• secondary succession,
• environmental degradation.

CONSEQUENCES OF ECOLOGICAL IMBALANCE

Ecological imbalance may result in:

• floods,
• landslides,
• diseases,
• erratic climatic events.

IMPORTANCE OF ECOLOGICAL UNDERSTANDING

Knowledge of ecosystems and biodiversity helps in:

• ecosystem protection,
• conservation,
• environmental management,
• maintaining ecological balance.

IMPORTANT UPSC FACTS

• Ernst Haeckel first used the term “ecology” in 1869.
• Nitrogen constitutes about 78% of atmosphere.
• Producers are green plants.
• Grazing food chain starts from plants.
• Food web is an interconnected network of food chains.
• Biogeochemical cycles maintain chemical balance in biosphere.
• Ecological balance is dynamic, not static.