Ecosystem Energy Flow

• Energy flow principles help understand ecosystem structure.
• Understanding autotrophs and heterotrophs defines energy conversion.
• Food chains are used to explain energy transfer.
• Ecological pyramids illustrate energy flow variations.
• Climate change impacts energy flow and ecosystem structure.

Energy Principles

• Energy is the ability to do work and cause changes.
• The First Law of Thermodynamics dictates that energy cannot be created or destroyed, only transformed.
• The Second Law of Thermodynamics states that energy transformations lead to waste and increased disorder.
• Energy is measure in Joules, and flow rate in Watts (J/s).

Key Definitions for Life

• Nutrition occurs through two mechanisms; 'trophs'
• Autotrophs convert abiotic energy sources into organic compounds, acting as producers in food chains.
• Heterotrophs use organic compounds for carbon and energy, functioning as primary, secondary, and tertiary consumers.
• Photoautotrophs use photosynthesis to convert sunlight into chemical energy by producing ATP and reduced NADP.
• Oxidation of inorganic substances transforms carbon dioxide into organic compounds in chemoautotrophs

Ecosystem Productivity

• 1 Kg of biomass traps about 30MJ of energy
• Energy is counted in Kg biomass equivalent
• Maximum photosynthetic efficiency is about 4% of incoming solar energy
• Actual yields are closer to 2%.
• Mitochondria produce 10,000 times more energy per gram than the sun.
• Gross Primary Production (GPP) is the total rate of organic carbon production by autotrophs.
• Net Primary Production (NPP) is GPP minus the autotrophs' respiration rate, representing biomass production by primary producers.
• Secondary production is the growth rate of heterotrophic biomass.
• Net Ecosystem Production is GPP minus the respiration of all organisms.
• Units are measured in Kg biomass per year

Ecological Communities

• General flow of energy in a community in order:
• Solar Energy -> Primary Producers -> Primary Consumers -> Secondary Consumers -> Top Predators
• Energy flow also includes: Primary Producers -> Nutrients
• Energy flow also includes: Consumers and Predators -> Waste -> Detritus Feeders -> Decomposers, returning to Primary Producers

Ecological Networks

• Ecological networks feature of many populations represented as a web of interconnected feeding habits
• Food webs are representations of predator-prey relationships only
• Trophic levels can be separated represented food webs with layers of organisms

Trophic Levels

• Primary producers/autotrophs are at the base (T1)
• Apex predators at the top (T4) of the food chain.

Terrestrial and Aquatic Ecosystems

• Average net primary productivity differs in terrestrial and aquatic ecosystems.

Energy Transfer

• About 10 percent of energy at one level is passed to the next.
• Most energy is lost as heat or used during metabolism.

Energy Flow

• Energy flow occurs through ecosystems via feeding rates
• Stock is the "nth" trophic level in the system
• Mortality and waste are removed to become Detritus and is broken down by Decomposers

Trophic Efficiency

• C(n) is Consumption rate [Js-1] (or GPP for autotrophs)
• P(n) is Net production rate [Js-1] (or NPP for autotrophs)
• R(n) is Respiration rate [Js-1]
• EC(n) Consumption efficiency = C(n) / P(n-1)
• EA(n) Assimilation efficiency = A(n) / C(n)
• EP(n) Production efficiency = P(n) / A(n)
• Trophic Efficiency (Ecological Efficiency) = EC x EA x EP
• Trophic Level Transfer Efficiency (TLTE) = (production at present trophic level) / (production at previous trophic level) x 100.
• P(n) / P(n-1) ≈ 0.1

Ecological Pyramids

• Classic view of biomass pyramid has producers at the bottom of food chain
• Average individual mass x number of individuals
• Number of individuals decreases exponentially with body mass.

Energy in Silver Springs, Florida

• Gross productivity decreases with each increase in trophic level.
• Efficiency of energy transfer between trophic levels is the major factor for length of food chains.
• The TLTE between the first two trophic levels was approximately 14.8% here

Predator-Prey Laws

• The ratio of predator-to-prey biomass is a key metric for trophic structure and community dynamics.
• Predator biomass scales with prey biomass in a sub-linear fashion.
• k < 1 and consistently close to ¼ across ecosystem types, implying biomass pyramids become more bottom-heavy with increased prey biomass

Pyramid Inversions

• Reality in marine environments is more complex – If k>0 then there would be inverted pyramids
• k < 0 occurs for bottom-heavy ecosystems where both abundance and biomass are concentrated in basal trophic levels.
• When k = 0, biomass is equally distributed across all body sizes
• Top-heavy ecosystems occur when k > 0.

Additional Information

• Climate change and fishing can impact aquatic communities
• These include alterations to environments, food chain and food web dynamics