LO14 Energy Flow and Nutrient Cycling in Ecosystems

Constant Energy Input

Energy enters ecosystems primarily from the sun in the form of solar radiation, transformed into chemical energy by autotrophs through photosynthesis or chemosynthesis.

Trophic Levels

Organisms in an ecosystem are grouped into trophic levels based on their feeding relationships: Primary Producers (autotrophs), Primary Consumers (herbivores), Secondary Consumers (carnivores), Tertiary Consumers (top predators), Decomposers and Detritivores (e.g., fungi, bacteria).

Gross Primary Production (GPP)

The total amount of light energy converted into chemical energy by autotrophs in a given period.

Net Primary Production (NPP)

The energy remaining after autotrophic respiration (Ra) that is available for consumption by other organisms. NPP = GPP - Ra.

Net Ecosystem Production (NEP)

Measures total biomass accumulation in an ecosystem. NEP = NPP - respiration of heterotrophs.

Trophic Pyramid

Biomass decreases at higher trophic levels due to energy loss at each level (as per the 10% rule).

10% Rule

Only about 10% of the energy at one trophic level is transferred to the next, leading to shorter food chains and upright energy pyramids.

Water Cycle

Involves processes like evaporation, condensation, precipitation, and transpiration. Water is essential for all organisms.

Carbon Cycle

Carbon is cycled through photosynthesis, respiration, burning of fossil fuels, and volcanic activity.

Nitrogen Cycle

Nitrogen is cycled through fixation (N2 to NH3), nitrification, denitrification, and through processes like legume crops and industrial fertilizers.

Phosphorus Cycle

Phosphorus cycles through rock weathering, leaching, and incorporation into organic molecules. It does not have a gaseous phase and is primarily limited to terrestrial systems.

Trophic Efficiency

Only about 10% of the energy at one trophic level is transferred to the next.

Eutrophication

Excessive nutrient runoff (especially nitrogen and phosphorus) leads to algal blooms, which deplete oxygen and create 'dead zones' in aquatic ecosystems.

Biological Magnification

Toxins, like pesticides, accumulate in organisms at higher trophic levels due to their low biomass and increase in concentration at each level.

Limiting Factors in Ecosystem Productivity (Aquatic)

Primary production is limited by both light and nutrients (e.g., nitrogen and phosphorus).

Limiting Factors in Ecosystem Productivity (Terrestrial)

Primary production is mainly influenced by temperature, moisture, and sunlight.

Constant input of energy

Energy is required to drive biological processes like growth, reproduction, and metabolism. It enters as solar radiation, is converted by producers, and is lost as heat, necessitating a continuous input.

GPP vs NPP

GPP (Gross Primary Production) is the total energy captured by producers. NPP (Net Primary Production) is the energy available after autotrophic respiration, representing the energy available to consumers.

Net Ecosystem Production (NEP)

NEP is the measure of total biomass accumulation in an ecosystem, showing whether the ecosystem is a carbon sink (gains carbon) or a carbon source (loses carbon).

Food chains and trophic levels

Because of energy loss at each trophic level, typically only 10% of energy is passed to the next level, which limits the number of trophic levels and forms an energy pyramid.

Decomposers and detritivores

Decomposers and detritivores break down nonliving organic material (detritus), recycling nutrients back into the ecosystem.

Eutrophication causes

Eutrophication is caused by excess nutrient runoff, especially nitrogen and phosphorus, leading to algae blooms, oxygen depletion, and dead zones in aquatic ecosystems.

Biological magnification

Biological magnification is the accumulation of toxins in organisms at higher trophic levels, leading to greater concentrations in top predators due to their lower biomass.

10% rule

The 10% rule states that only about 10% of the energy at one trophic level is passed on to the next, with the rest lost as heat or used in respiration.

Limiting factor in aquatic primary production

In aquatic ecosystems, primary production is mainly limited by nutrient availability, especially nitrogen and phosphorus.

Role of nitrogen-fixing bacteria

Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into ammonia (NH3), making nitrogen available to plants for growth.

Phosphorus cycle vs carbon and nitrogen cycles

The phosphorus cycle lacks a gaseous phase and primarily involves the movement of phosphorus through soil, water, and organisms, while carbon and nitrogen cycles have gaseous phases.

Energy pyramids and biomass

Energy pyramids reflect the loss of energy at each trophic level, with about 90% of energy lost as heat, leaving less energy available for higher trophic levels.

Role of decomposers in nutrient cycling

Decomposers break down dead organic matter, releasing nutrients back into the environment, which are then available for producers to use.

Temperature and decomposition rates

Decomposition is faster in warmer ecosystems because higher temperatures increase the activity of decomposers.

Carbon cycle

The carbon cycle involves the movement of carbon through the atmosphere, living organisms, and ecosystems via processes like photosynthesis, respiration, and burning of fossil fuels.