An ecosystem is a dynamic complex of living organisms (plants, animals, and microbes) interacting with one another and with their non-living environment (air, water, and mineral soil) as a system. Ecosystems can vary greatly in size and type, from small ponds to large forests or oceans. The biosphere is a global ecosystem encompassing all local ecosystems on Earth.

Examples of ecosystems include:

• Terrestrial Ecosystems: Forests, grasslands, deserts
• Aquatic Ecosystems: Ponds, lakes, wetlands, rivers, estuaries
• Man-made Ecosystems: Crop fields, aquariums

Components of an ecosystem include biotic (living) and abiotic (non-living) factors.

The two important structural features are:

• Species Composition: All plants, animals, and microbes present in an ecosystem.
• Stratification: Vertical distribution of species in an ecosystem.

Ecosystems perform four major functions:

• Productivity: The rate of biomass production through the conversion of energy by producers.
• Decomposition: The process of breaking down organic matter into simpler compounds.
• Energy Flow: The transfer of energy from one organism to another through various trophic levels.
• Nutrient Cycling: The recycling of nutrients through the biotic and abiotic components of the ecosystem.

Energy transfer occurs through food chains and webs:

• Food Chain: A linear sequence of energy transfer from producers to consumers.
• Food Web: A complex network of interconnected food chains.

Nutrient Cycling: The movement of nutrients between organisms and their physical environment, allowing ecosystems to maintain balance and productivity.

Primary Productivity: The amount of biomass or organic matter produced by plants through photosynthesis.

Two types of primary productivity:

• Gross Primary Productivity (GPP): The total amount of organic matter produced by photosynthesis.
• Net Primary Productivity (NPP): The amount of energy available to consumers after some energy is used for respiration (NPP = GPP - R).

Decomposition: The process where complex organic matter is broken down into simpler substances.

Steps involved in decomposition:

• Fragmentation: Detritus is broken into smaller particles by detritivores (e.g., earthworms).
• Leaching: Water-soluble substances are carried down to the soil horizon.
• Catabolism: Enzymatic breakdown of detritus into inorganic compounds by decomposers (bacteria and fungi).
• Humification: Formation of dark-colored amorphous substances called humus.
• Mineralization: Degradation of humus, releasing inorganic nutrients.

A food chain is a series of organisms each dependent on the next as a source of food. There are two main types of food chains:

• Grazing Food Chain (GFC): Starts with producers (plants) and involves herbivores and carnivores.
• Detritus Food Chain (DFC): Begins with dead organic matter and is decomposed by microbes and fungi.

Energy Flow: In a food chain, energy moves in one direction, from producers to consumers. Only 10% of energy is transferred from one trophic level to the next, while 90% is lost as heat.

Trophic Levels: Each step in the food chain is a trophic level. Primary producers are at the first trophic level, followed by herbivores, and then carnivores.

Ecological pyramids represent the relationships among organisms at different trophic levels. They can be classified into:

• Pyramid of Numbers: Shows the number of organisms at each trophic level. It can be upright or inverted.
• Pyramid of Biomass: Illustrates the total biomass at each trophic level. It can be upright (terrestrial ecosystems) or inverted (aquatic ecosystems).
• Pyramid of Energy: Always upright as energy decreases at each successive trophic level due to the loss of energy as heat.

Ecological Succession: The gradual process of change and replacement of species in a community, leading to the establishment of a stable climax community.

Two types of ecological succession:

• Primary Succession: Occurs in an area where no life previously existed (e.g., bare rocks).
• Secondary Succession: Occurs in areas where life previously existed but was destroyed (e.g., after a forest fire).

Two main types of succession based on the nature of the habitat:

• Hydrarch Succession: Starts in aquatic environments and progresses toward land (e.g., from ponds to forests).
• Xerarch Succession: Begins in dry or arid environments and moves toward more mesic (moist) conditions (e.g., from bare rocks to forest).

Climax Community: The stable and mature community that develops at the final stage of succession. It remains relatively unchanged until disrupted by a disturbance.

Nutrient Cycling: The recycling of nutrients between living organisms and their physical environment. It ensures that nutrients are reused within ecosystems.

Nutrient cycles can be classified into:

• Gaseous Cycles: Nutrients (e.g., carbon, nitrogen) are cycled between the atmosphere and organisms.
• Sedimentary Cycles: Nutrients (e.g., phosphorus, sulfur) are cycled between the Earth's crust and organisms.

The carbon cycle is the process through which carbon is exchanged between the atmosphere, oceans, and organisms. It plays a crucial role in regulating the Earth's climate and supporting life.

Carbon dioxide is absorbed by plants during photosynthesis and released back into the atmosphere through respiration, decomposition, and human activities like burning fossil fuels.

The phosphorus cycle involves the movement of phosphorus through rocks, soil, water, and living organisms. Unlike the carbon cycle, phosphorus does not cycle through the atmosphere.

Phosphates are released from rocks through weathering and are absorbed by plants, which pass them on to animals through the food chain. Decomposers return phosphorus to the soil, where it can be reused.

Ecosystem Services: The benefits provided by ecosystems to humans. These include:

• Provisioning Services: Products obtained from ecosystems, such as food, water, timber, and fiber.
• Regulating Services: Benefits from ecosystem processes, including air quality regulation, climate regulation, and water purification.
• Supporting Services: Services that support the functioning of ecosystems, such as nutrient cycling and soil formation.
• Cultural Services: Non-material benefits, including recreational, aesthetic, and spiritual values.