An Ecosystem is a dynamic system of all the living organisms (biotic community) in a particular area, interacting with each other and with their non-living (abiotic) physical environment.
The term was coined by Arthur Tansley in 1935.
It is the fundamental unit of ecology, focusing on the interactions that link living and non-living components.
Examples: A pond, a forest, a desert, a fallen log.
Ecosystem Structure
This refers to the "parts list" of the ecosystem; its static components.
Abiotic Components: The non-living parts (e.g., sunlight, temperature, water, soil, minerals).
Biotic Components: The living parts, organized by trophic (feeding) levels (e.g., producers, consumers, decomposers).
Ecosystem Function
This refers to the "processes" and "jobs" that occur within the ecosystem.
Energy Flow: The one-way passage of energy (from the sun) through the system.
Nutrient Cycling: The circular movement of chemical elements (like carbon, nitrogen) between biotic and abiotic components.
Productivity: The rate at which biomass is created.
Decomposition: The breakdown of dead organic matter.
In short: Structure is the 'what', Function is the 'how'.
2. Components of Ecosystem
Diagram: A flowchart showing "Sunlight" as the primary energy source.
1. "Abiotic Components" box (Climate, Soil, Water).
2. "Biotic Components" box, which contains:
a. "Producers (Autotrophs)" (e.g., Plants) - get energy from Sun.
b. "Consumers (Heterotrophs)" (e.g., Animals) - get energy from Producers.
c. "Decomposers (Saprotrophs)" (e.g., Fungi) - get energy from dead Producers & Consumers.
Decomposers break down matter into "Nutrient Pool" (abiotic), which Producers then use.
They obtain energy by breaking down dead organic matter (detritus) from all trophic levels.
They are essential for recycling nutrients back into the soil for producers to use.
Examples: Bacteria and fungi.
3. Types of Ecosystem
Terrestrial Ecosystem (Land-based)
These are ecosystems found on land. Their character is primarily determined by climate (temperature, rainfall) and dominant vegetation.
Forest Ecosystem: Dominated by trees (e.g., tropical rainforest, temperate deciduous forest, taiga).
Grassland Ecosystem: Dominated by grasses (e.g., savanna, prairie, steppe).
Desert Ecosystem: Characterized by very low rainfall and sparse, adapted vegetation (e.g., hot desert like the Sahara, cold desert like the Gobi).
Tundra Ecosystem: A cold, treeless biome with a permanently frozen subsoil (permafrost).
Aquatic Ecosystem (Water-based)
These are ecosystems found in water bodies. They are often classified by salinity (salt content).
Freshwater Ecosystems (Low salt content)
Lentic (Standing Water): Ponds, lakes.
Lotic (Flowing Water): Rivers, streams.
Wetlands: Areas where soil is saturated (e.g., marshes, swamps).
Marine Ecosystems (High salt content)
Ocean Ecosystem: The vast open ocean, with zones based on depth and light.
Coral Reef: Highly diverse and productive shallow-water ecosystems built by coral animals.
Estuarine Ecosystems (Brackish water)
Estuary: An area where a freshwater river meets the saltwater ocean. The mixing creates "brackish" water. These are extremely productive ecosystems, serving as "nurseries" for many fish and shellfish.
4. Concept of Species, Population and Community
These are the hierarchical levels of organization for the biotic components of an ecosystem.
Species: A group of similar organisms that can interbreed and produce fertile offspring. (e.g., a "Grey Wolf").
Population: A group of individuals of the same species living in the same area at the same time. (e.g., "The pack of Grey Wolves in Yellowstone Park").
Community: A group of different populations (all the different species) living and interacting in the same area. (e.g., "The Grey Wolves, elk, bison, and aspen trees in Yellowstone Park").
Remember the hierarchy: Individual Organism → Population (one species) → Community (many species) → Ecosystem (community + abiotic factors).
5. Energy Flow in an Ecosystem
The flow of energy in an ecosystem is UNIDIRECTIONAL (one-way).
It does not cycle. It flows in, is transferred, and is eventually lost as heat.
Input: Virtually all energy for Earth's ecosystems comes from the sun.
Capture: Producers (plants) capture this solar energy via photosynthesis and store it in the chemical bonds of sugar (biomass).
Transfer: Energy is transferred to primary consumers when they eat producers, and then to secondary consumers when they eat primary consumers, and so on.
Loss: At each and every step, a large amount of energy (around 90%) is lost. This energy is used for the organism's own metabolism (movement, breathing, keeping warm) and is ultimately dissipated as heat.
This massive loss of energy at each step is known as the 10% Law (only about 10% of energy is passed on). This is the second law of thermodynamics in action (entropy/disorder always increases).
6. Food Chain and Food Web
These are models that show the flow of energy in an ecosystem.
Food Chain
A simple, linear pathway showing the feeding relationships and energy flow from one organism to another. Each step is a trophic level.
Example 2 (Aquatic): Algae (Producer) → Zooplankton (Primary Consumer) → Small Fish (Secondary Consumer) → Large Fish (Tertiary Consumer)
Food Web
A food web is a more realistic and complex model that shows the interconnected network of multiple food chains within a community. It recognizes that most organisms eat, and are eaten by, more than one species.
Food webs are more stable than simple food chains. If one food source is removed (e.g., a disease kills all the rabbits), a fox (in a food web) can survive by eating more mice or squirrels.
Diagram: A web diagram. "Plants" at the bottom. Arrows point to "Rabbit," "Mouse," and "Grasshopper." "Rabbit" and "Mouse" arrows point to "Fox." "Mouse" and "Grasshopper" arrows point to "Owl."
7. Ecological Pyramids
These are graphical representations of the trophic structure of an ecosystem. They show the relative amounts of a given quantity (energy, biomass, or numbers) at each successive trophic level. The producers always form the base (bottom level).
Pyramid of Energy
Shows the amount of energy (e.g., in Joules) available at each trophic level.
It is ALWAYS UPRIGHT.
This is because energy is always lost (as heat) at each transfer, following the 10% Law.
Pyramid of Biomass
Shows the total biomass (total dry weight of all organisms) at each level.
Usually Upright: In most terrestrial ecosystems (like a forest), the total biomass of producers (trees) is vastly larger than the biomass of herbivores.
Can be Inverted: In some aquatic ecosystems. The producers are phytoplankton, which have a tiny total biomass but reproduce extremely rapidly. They are consumed so quickly by zooplankton that the zooplankton's biomass at any given moment is actually greater.
Pyramid of Numbers
Shows the number of individual organisms at each trophic level.
Usually Upright: In a grassland, there are millions of grass plants, thousands of grasshoppers, and a few birds.
Can be Inverted: When the producer is very large. For example, a single large tree (1 producer) can support thousands of insects (primary consumers).
Crucial Exam Point: The Pyramid of Energy is the only pyramid that is *always* upright. Pyramids of numbers and biomass can be inverted.
8. Carrying Capacity: Definition
Carrying Capacity (K) is defined as the maximum population size of a given species that a particular environment can sustain indefinitely, given the available food, water, and other resources.
It is not a fixed number, but a dynamic concept that can change if the environment changes (e.g., a drought would lower the carrying capacity).
When a population grows, it eventually encounters limiting factors (like scarce food or increased disease), which cause the growth rate to slow down and stop. The population then typically fluctuates around this carrying capacity. This is shown by the logistic (S-shaped) growth curve.