Ecology, Ecosystem & Biodiversity

• Ecology is the study of how organisms interact with each other and with their non-living surroundings.
• The word comes from Greek oikos = home, so ecology means the study of the home of life.
• Energy flows from the Sun → plants → animals → decomposers, while materials are recycled endlessly.
• The four big ideas of this chapter are the ecosystem, energy flow, nutrient cycling and biodiversity.
• Levels of organisation studied are organism → population → community → ecosystem → biome → biosphere.

Ecology is the study of how organisms interact with each other and with their non-living surroundings.

The word comes from Greek oikos = home, so ecology means the study of the home of life.

Energy flows from the Sun → plants → animals → decomposers, while materials are recycled endlessly.

• An ecosystem is a unit where living organisms interact with each other and their physical environment.
• NCERT calls it the structural and functional unit of nature; a pond, forest or aquarium is one.
• Abiotic components are non-living factors – air, water, soil, temperature and light.
• Biotic components are all living things, grouped as producers, consumers and decomposers.
• Key structural features are species composition (which species) and stratification (vertical layering).
• A large climate-and-vegetation region is a biome; the exact spot an organism lives in is its habitat.
• Abiotic — Air, water, soil, light, temperature
• Biotic — Producers, consumers, decomposers

An ecosystem is a unit where living organisms interact with each other and their physical environment.

Abiotic components are non-living factors – air, water, soil, temperature and light.

Biotic components are all living things, grouped as producers, consumers and decomposers.

Key structural features are species composition (which species) and stratification (vertical layering).

A large climate-and-vegetation region is a biome; the exact spot an organism lives in is its habitat.

• The four most important abiotic factors are temperature, water, light and soil.
• Life survives in extremes – deserts, ocean trenches, polar permafrost, hot thermal springs and the human gut.
• An adaptation is a useful feature evolved through natural selection to help survival and reproduction.
• Desert (dry-loving) animals are called xerocoles; desert plants storing water are xerophytes.
• Salt-loving plants are called halophytes; water-loving plants are hydrophytes.
• A cactus storing water and spiny leaves is a classic desert adaptation.
• Xerophyte — Dry / desert habitat
• Halophyte — Saline (salty) soil
• Hydrophyte — Aquatic habitat
• Mesophyte — Moderate moisture

Life survives in extremes – deserts, ocean trenches, polar permafrost, hot thermal springs and the human gut.

An adaptation is a useful feature evolved through natural selection to help survival and reproduction.

Desert (dry-loving) animals are called xerocoles; desert plants storing water are xerophytes.

Salt-loving plants are called halophytes; water-loving plants are hydrophytes.

A cactus storing water and spiny leaves is a classic desert adaptation.

• Producers (autotrophs) make their own food from CO2 and water using sunlight – green plants, algae, phytoplankton.
• Producers are the entry point of energy into every ecosystem.
• Consumers (heterotrophs) cannot make food; all animals ultimately depend on plants.
• Herbivores are primary consumers; carnivores are secondary/tertiary consumers.
• Omnivores like humans, crows and cockroaches eat both plants and animals.
• Decomposers (saprotrophs) – fungi and bacteria – break down dead matter (detritus) and recycle nutrients.
• Producer — Sunlight + CO2 — Green plant, algae
• Herbivore — Plants — Deer, grasshopper
• Carnivore — Animals — Snake, eagle
• Decomposer — Dead matter — Fungi, bacteria

Producers (autotrophs) make their own food from CO2 and water using sunlight – green plants, algae, phytoplankton.

Producers are the entry point of energy into every ecosystem.

Consumers (heterotrophs) cannot make food; all animals ultimately depend on plants.

Herbivores are primary consumers; carnivores are secondary/tertiary consumers.

Omnivores like humans, crows and cockroaches eat both plants and animals.

Decomposers (saprotrophs) – fungi and bacteria – break down dead matter (detritus) and recycle nutrients.

• A trophic level is the feeding position in a food chain; it is a functional level, not a fixed species.
• Producers are the 1st trophic level, herbivores the 2nd, carnivores the 3rd, and so on.
• A food chain is a straight-line who-eats-whom, e.g. grass → grasshopper → frog → snake → eagle.
• A grazing food chain (GFC) starts with living plants and dominates aquatic ecosystems.
• A detritus food chain (DFC) starts with dead matter; on land more energy flows through the DFC.
• Many interlinked chains form a food web, which makes the ecosystem more stable.
• Grazing (GFC) — Living green plants — Aquatic ecosystems
• Detritus (DFC) — Dead organic matter — Terrestrial ecosystems

A trophic level is the feeding position in a food chain; it is a functional level, not a fixed species.

Producers are the 1st trophic level, herbivores the 2nd, carnivores the 3rd, and so on.

A food chain is a straight-line who-eats-whom, e.g. grass → grasshopper → frog → snake → eagle.

A grazing food chain (GFC) starts with living plants and dominates aquatic ecosystems.

A detritus food chain (DFC) starts with dead matter; on land more energy flows through the DFC.

Many interlinked chains form a food web, which makes the ecosystem more stable.

• The Sun is the energy source for almost all ecosystems; the exception is deep-sea hydrothermal vents (chemical energy).
• Less than 50% of sunlight is PAR (photosynthetically active radiation) usable by plants.
• Plants capture only about 2–10% of PAR, yet this sustains all life.
• Energy flow is unidirectional (Sun → producers → consumers → decomposers); it never flows backward.
• The 10% law states only about 10% of energy passes to the next trophic level; ~90% is lost as heat.
• Example: 1000 units in plants → 100 in herbivores → 10 in carnivores.

The Sun is the energy source for almost all ecosystems; the exception is deep-sea hydrothermal vents (chemical energy).

Less than 50% of sunlight is PAR (photosynthetically active radiation) usable by plants.

Plants capture only about 2–10% of PAR, yet this sustains all life.

Energy flow is unidirectional (Sun → producers → consumers → decomposers); it never flows backward.

The 10% law states only about 10% of energy passes to the next trophic level; ~90% is lost as heat.

• An ecological pyramid shows the relationship between trophic levels by number, biomass or energy.
• The pyramid of energy is always upright because energy decreases at every higher level.
• The pyramid of numbers can be inverted, e.g. one big tree supporting many insects.
• The pyramid of biomass is inverted in the sea (small phytoplankton support larger fish).
• Producers always form the base of the pyramid.
• Energy — No – always upright
• Number — Yes (e.g. tree ecosystem)
• Biomass — Yes (e.g. aquatic ecosystem)

An ecological pyramid shows the relationship between trophic levels by number, biomass or energy.

The pyramid of energy is always upright because energy decreases at every higher level.

The pyramid of numbers can be inverted, e.g. one big tree supporting many insects.

The pyramid of biomass is inverted in the sea (small phytoplankton support larger fish).

Producers always form the base of the pyramid.

• Nutrient cycling is the repeated movement of nutrients between living organisms and the environment.
• Gaseous cycles (carbon, nitrogen, oxygen) have their main reservoir in the atmosphere.
• Sedimentary cycles (phosphorus, sulphur) have their reservoir in rocks and soil.
• In the nitrogen cycle, bacteria fix atmospheric N2 into usable forms; legumes host Rhizobium.
• In the carbon cycle, photosynthesis removes CO2 and respiration/burning returns it.
• Decomposers are essential – they release locked nutrients back into the soil.
• Gaseous — Atmosphere — Carbon, nitrogen
• Sedimentary — Earth's crust / soil — Phosphorus, sulphur

Nutrient cycling is the repeated movement of nutrients between living organisms and the environment.

Gaseous cycles (carbon, nitrogen, oxygen) have their main reservoir in the atmosphere.

Sedimentary cycles (phosphorus, sulphur) have their reservoir in rocks and soil.

In the nitrogen cycle, bacteria fix atmospheric N2 into usable forms; legumes host Rhizobium.

In the carbon cycle, photosynthesis removes CO2 and respiration/burning returns it.

Decomposers are essential – they release locked nutrients back into the soil.

• Biodiversity is the variety of all life forms – genes, species and ecosystems on Earth.
• Genetic diversity is variation within a species (e.g. many rice varieties).
• Species diversity is the number of different species in an area.
• Ecosystem diversity is the variety of habitats like forests, wetlands and deserts.
• Biodiversity is highest near the equator (tropical rainforests) and falls toward the poles.
• Maximum species of butterflies and other groups occur in the tropics due to stable warm climate.
• Genetic — Variation within a species
• Species — Number of species in an area
• Ecosystem — Variety of habitats

Biodiversity is the variety of all life forms – genes, species and ecosystems on Earth.

Genetic diversity is variation within a species (e.g. many rice varieties).

Species diversity is the number of different species in an area.

Ecosystem diversity is the variety of habitats like forests, wetlands and deserts.

Biodiversity is highest near the equator (tropical rainforests) and falls toward the poles.

• A lichen is a partnership of an alga and a fungus – the alga makes food, the fungus gives shelter.
• This algae-fungus relationship is called symbiosis (mutualism), benefiting both.
• Lichens are excellent indicators of air pollution and do not grow in polluted areas.
• Mutualism benefits both; commensalism benefits one with no harm to the other.
• Parasitism benefits one and harms the host; predation is one species eating another.
• Competition occurs when species fight for the same limited resource.
• Mutualism — Benefit — Benefit
• Commensalism — Benefit — No effect
• Parasitism — Benefit — Harm
• Predation — Benefit — Harm
• Competition — Harm — Harm

A lichen is a partnership of an alga and a fungus – the alga makes food, the fungus gives shelter.

This algae-fungus relationship is called symbiosis (mutualism), benefiting both.

Lichens are excellent indicators of air pollution and do not grow in polluted areas.

Mutualism benefits both; commensalism benefits one with no harm to the other.

Parasitism benefits one and harms the host; predation is one species eating another.

Competition occurs when species fight for the same limited resource.

• DDT is a non-biodegradable chlorinated insecticide (pesticide) that persists in the environment.
• Biomagnification is the increasing concentration of toxins like DDT up the food chain.
• The vulture population in India collapsed mainly due to the drug diclofenac in cattle carcasses.
• Ozone in the stratosphere protects the biosphere from harmful ultraviolet (UV) radiation.
• Lichens serve as biological indicators of clean air.
• Ecological succession is the orderly change of a community over time toward a stable climax.

DDT is a non-biodegradable chlorinated insecticide (pesticide) that persists in the environment.

Biomagnification is the increasing concentration of toxins like DDT up the food chain.

The vulture population in India collapsed mainly due to the drug diclofenac in cattle carcasses.

Ozone in the stratosphere protects the biosphere from harmful ultraviolet (UV) radiation.

Lichens serve as biological indicators of clean air.

Ecological succession is the orderly change of a community over time toward a stable climax.

• In-situ conservation protects species in their natural home – national parks, sanctuaries, biosphere reserves.
• Ex-situ conservation protects species outside their habitat – zoos, botanical gardens, seed banks.
• The IUCN Red List classifies species by extinction risk.
• The Gangetic river dolphin is listed as Endangered and is India's National Aquatic Animal.
• Biodiversity hotspots are species-rich, highly threatened regions (e.g. Western Ghats, Himalaya).
• A keystone species has a large effect on its ecosystem relative to its numbers.
• In-situ — Natural habitat — National park, sanctuary
• Ex-situ — Off-site — Zoo, seed bank

In-situ conservation protects species in their natural home – national parks, sanctuaries, biosphere reserves.

Ex-situ conservation protects species outside their habitat – zoos, botanical gardens, seed banks.

The IUCN Red List classifies species by extinction risk.

The Gangetic river dolphin is listed as Endangered and is India's National Aquatic Animal.

Biodiversity hotspots are species-rich, highly threatened regions (e.g. Western Ghats, Himalaya).

A keystone species has a large effect on its ecosystem relative to its numbers.