ECOSYSTEMS

Chapter - 3

An ecosystem is a natural unit consisting of all plants, animals, and micro-organisms in an area functioning together with all the non-living physical factors of the environment.

According to British ecologist Arthur Tansley (1935), an ecosystem is a system that arises from the integration of all living and non-living factors of the environment.

Ecology

Ecology is the study of how living and non-living factors affect each other in an environment. An ecosystem is the basic and functional unit of ecology.

Ecosystem

Classification of Ecosystems

Natural Ecosystems Man-made Ecosystems (aquaria, garden, dams & cropland of maize,wheat, rice).

Terrestrial Ecosystems

Aquatic Ecosystems

Fresh water Ecosystems

Marine Ecosystems

Running water Ecosystems (lotic)

Standing water Ecosystems (lentic)

Forest Ecosystems

Grass land Ecosystems

Desert Ecosystems

Natural Ecosystems Man-made Ecosystems

What is the different between natural and manMade ecosystem?

Structure of an Ecosystem

Living (Biotic) Components

• Producers• Consumers ( primary, secondary and tertiary)• Decomposers(Maintains biological cycle)

Non-living (Abiotic) Components

• Organic• Inorganic• Physical

Biotic Components of Ecosystems

• Producers (or autotrophs)

Green plants and some bacteria which manufacture their own food.

• Consumers (or heterotrophs)

Animals which obtain their food from producers•Primary consumers•Secondary consumers•Tertiary consumers

• Decomposers

Bacteria and fungi that decompose deadorganic matter and convert it intosimpler parts

Abiotic Components of an Ecosystem

Organic Carbohydrates Lipids Proteins

Inorganic Water Ammonia Gases

Climatic Rainfall Humidity Temperature

Limiting factorFactors which restrict the further growth of populationAvailability of foodWaterShelterSpace

• Food chain and food web

•Energy flow

• Cycling of matter (chemicals)

Functions of an Ecosystem

Food Chain

The transfer of food energy from the source (plants) through a series of organisms by repeated eating and being eaten up is referred as food chain.

Food Web

The interlocking pattern formed by several food chains that are linked together is called a food web.

Significance of food chain

• Food chains are important for maintaining and regulating the population size

• Ecological balance• biomagnification

Flow of Energy in an Ecosystem

First Law of Energy

Energy can neither be created nor be destroyed

Second Law of Energy

No energy transformations are 100% efficient

Ten-percent Rule of Energy

Only 10% of food energy is transferred from one trophic level to another

Producer → primary consumer → secondary consumer → tertiary consumer(1000 Kcal) (100 Kcal) (10 Kcal) (1 Kcal)

Biogeochemical Cycling

The cyclic movement of minerals from their reservoirs (air, water, and soil) to the living components and back to the reservoirs is called nutrient cycling or biogeochemical cycles.

Phosphorus Cycle

Carbon Cycle Nitrogen cycle

Ecological Pyramid

The graphical representations of different trophic levels in an ecosystem is known as ecological pyramid .

They are used to illustrate the feeding relationships between organisms.

Types of Ecological Pyramids

•Pyramid of number

•Pyramid of biomass

•Pyramid of energy

Pyramid of Number

Pyramid of number is used to show the number of individuals in each trophic level.

It is upright in case of grassland and pond ecosystems.

In some cases, the pyramid of number is inverted.

For example, in case of forest ecosystem.

Pyramid of Biomass

The pyramid of biomass is used to show the total biomass of individuals at each trophic level.

It is better than the pyramid of number for showing the relationships between organisms.

Pyramid of biomass is upright in case of grassland and forest ecosystemsand inverted in case of pond ecosystems.

Pyramid of energy

Pyramid of energy is used to show the amount of energy transferred between trophic levels. It provides the best representation of the overall nature of an ecosystem.

The pyramid of energy flow is always upright because there is always loss of energy while moving from lower trophic level to higher trophic level. Therefore, the energy reaching the next trophic level is always less compared to that in the previous trophic level.

Ecological succession is the gradual process by which ecosystems change and develop over time. It is therefore a series of predictable temporary communities or stages leading up to a climax community. Each stage/temporary community is called a successional stage or seral stage. Each step prepares the land for the next successional stage. All habitats are in the state of constant ecological succession.

Types of Succession

Primary succession

Primary succession refers to a series of community changes which occur on an entirely new habitat which has never been colonized before. For example, a newly quarried rock face or sand dunes. (pioneer and climax community)

Secondary succession

Secondary succession refers to a series of community changes which take place on a previously colonized, but disturbed or damaged habitat. For example, land obtained after felling trees in a woodland, land clearance, or fire.  

Ecological Succession

Ecosystem characteristic that changes during Succession

Characteristics Stage

Initial Climax

1. Size of individual Small Large

2. Community organization Simple Complex

3. Food Chain & food Web Simple Complex

4. Efficiency of energy use Low High

5. Nutrient conversion Low High

• Two primary cause that initiate the ecological succession

• An established species and impact of external natural forces, which try to alter the environmental condition of that area

• Ex. Hardwood tree replacing red pine• Ecosystem is continuously changing and

reorganizing,• ecological succession refers to orderly changes

in composition or structure of ecosystem

Process of ecological succession

• Nudation• Invasion Migration (dispersal) Ecesis (establishment) Aggregation• Competition• Stabilization

Forest Ecosystem

Inorganic and organic substances found in thesoil, climatic factors, e.g., temperature, humidity, rainfall, and light.

Abiotic Components

Producers Different kinds of trees depending upon the climate

Consumers Different kinds of primary, secondary, and tertiary consumers, e.g., deer, elephant, moles, snakes, lizards, lion, and tiger

DecomposersThese are various kinds of bacteria and fungi

Biotic Components

Forest ecosystem

• tropical rain forests (small mammals, reptiles birds, monkeys, predators like tigers, jaguars etc. plant biodiversity Tall tree, dense canopy.)

• temperate forests (deciduous plants like oaks, maples, coniferous plants like pines, ferns, lichens and mosses are also found.)

• coniferous forests (spruce, pine fir)• Tundra (mosses, lichens, grasses and some dwarf trees;

animals like arctic foxes, hares, snowy owls; it is fragile ecosystem)

Tropical Forest: Vertical stratification with trees in canopy blocking light to bottom strata. Many trees covered by epiphytes (plants that grow on other plants).

Temperate Deciduous Forest: Mid-latitudes with moderate amounts of moisture, distinct vertical strata: trees, understory shrubs, herbaceous sub-stratum. Loss of leaves in cold, many animals hibernate or migrate then. Original forests lost from North America by logging and clearing.

Coniferous forest: Largest terrestrial biome on earth, old growth forests rapidly disappearing, usually receives lots of moisture as rain or snow.

Tundra: Permafrost (Permanent frozen ground), bitter cold, high winds and thus no trees. Has 20% of land surface on earth.

Grassland Ecosystem

ProducersMainly grasses with a few scattered trees Consumers Deer, rabbit, giraffe, etc., are herbivores,while wolf, leopard, etc., are carnivores

Decomposers Mainly bacteria and fungi

Abiotic Components

Inorganic elements (C, H, O, N, P, S), climatic components, temperature, rainfall, light, etc.

Biotic Components

Grassland ecosystem

• Grasslands(grazing animals like wild horses, kangaroos, zebra as well as predators like wolves, cheetas etc. )

• Tropical grassland (hot through out the year) (savannas)

• Temperate grassland (hot during summer and very cold during winter)

Temperate Grassland: Marked by seasonal drought and fires, and grazing by large animals. Rich habitat for agriculture, very little prairie exists in US today.

Desert Ecosystem

Producers Predominantly thorny shrubs, cactus, opuntia, etc.

Consumers Different insects, lizards, reptiles, nocturnal rodents, birds, etc.

Decomposers Various bacteria and fungi

Low rainfall, high temperature, and sandy soil

Abiotic Components

Biotic Components

Desert: Sparse rainfall (< 30 cm per year), plants and animals adapted for water storage and conservation. Can be either very, very hot, or very cold (e.g. Sahara, Thar, Antarctica)

Pond Ecosystem

It includes organic and inorganic substances,atmospheric gases dissolved in water, mineralsfound in dissolved state, etc.

Producers Submerged floating and emergent aquatic plantsFor example, nelumbo, hydrilla, chara, etc. Consumers May be primary, secondary, or tertiary, e.g., small fishes, beetles, mollusca, crustaceans, etc.

DecomposersChiefly bacteria, actinomycetes, fungi, etc.

Abiotic Components

Biotic Components

The Global Ocean

• Single ocean, great depths• Largely unexplored• Greater biodiversity than on land• Provides many ecosystem services

Zones of the Ocean

• Coastal zone• Open ocean:

– euphotic zone– bathyal zone – abyssal zone

Figure 4.1 The Zones of the Ocean

Marine environment with zonation.

Intertidal Zone: Alternately submerged and exposed by daily cycle of tides. Often polluted by oil that decreases biodiversity.

Figure 4.2 The Coastal Zone

Estuary: Place where freshwater stream or river merges with the ocean. Highly productive biome; important for fisheries and feeding places for water fowl. Often heavily polluted from river input so many fisheries are now lost.

Estuary•An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea•Estuaries form a transition zone between river environments and ocean environments and are subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment•Estuaries provide habitats for a large number of organisms and support very high productivity. Estuaries provide habitats for many fish nurseries, depending upon their locations in the world, such as salmon and sea trout.