- Food chain: linear flow chart of who eats whom and direction of nutrient and energy transfer
- Food web: linked group of food chains (animals have more than one food source)
Conservation of Mass
- Matter, like energy, cannot be created or destroyed.
- But elements can cycle–be gained or lost by an ecosystem
- Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products
- Ecosystems depend on constant input of energy
Ecological/Trophic Efficiency
- “Proportion of energy represented at one trophic lvl that is transferred to the next lvl”
- Always less than production efficiency
- ~1% of the solar energy that reaches the surface of the earth is converted into organic matter
- Transfer of energy between trophic lvls is inefficient → ~only 10% of the productivity of one trophic lvl is transferred to the next lvl
- Remaining 90% is used for metabolic activities, passed thru feces, or transferred to detritivores
- Most energy for respiration and other metabolic activities is ultimately lost as heat
- Heat is energy that cannot be harnessed by organisms to do work → represents energy lost from the ecosystem
- So ultimately all energy originally gained through NPP is lost as heart
- BUT chemicals, nutrients and matter recycled in an ecosystem (unlike heat)
- Heat is energy that cannot be harnessed by organisms to do work → represents energy lost from the ecosystem
- Bcuz ecological efficiency is so low, almost all animals used for food/work are herbivores
- Carnivores require more energy to sustain themselves
- Changes in energy availability can result in…
- Changes in population size & density
- Disruptions to an ecosystem: Species have adaptations that aid survival when energy availability changes
- Ex: fat as energy, lose/grow leaves, migration, hibernation, lower metabolic rate
- Exist reproductive strategies in response to energy availability
- Produce lots of offspring at one
- Energy efficient when not enough resources
- Some produce few offspring at one
- Energy efficient in stable environments
- Ex: sunlight can affect number and size of trophic levels
- Produce lots of offspring at one
Energy Flow and Chemical Cycling 
- Chemical Cycling: plants take chemicals from soil & air → chemicals passed to herbivores → decomposers break down dead matter, releasing chemicals back to the soil
- Energy Flow: Energy enters most ecosystems as sunlight → converted to chemical energy by autotrophs → passed to heterotrophs in the organic compounds of food → dissipated as heat when energy used for work
- Both energy and chemicals are transformed in ecosystems through photosynthesis and feeding relationships. But unlike chemicals, energy cannot be recycled.
How do Organisms Regulate Body Temp and Metabolism?
- Endotherms use thermal energy generated by metabolism
- Ex: changes in heart rate, fat storage, muscle contractions (shivering)
- Metabolic Rate/O2 consumption rate increases with decreasing temperature
- Spend more energy to maintain internal temp
- Ectotherms lack efficient body temperature regulating mechanisms
- Rely on behavior: moving in and out sun, eating
- Metabolic Rate/O2 consumption rate increases with increasing temperature
Primary Productivity
- Organisms use energy to grow and reproduce
- Primary productivity: amount of organic matter produced through photosynthetic (or chemosynthetic) activity per unit of time; components of primary productivity…
- Gross primary productivity (GPP): rate at which producers acquire chemical energy before any of this energy is used for metabolism
- Net primary productivity (NPP): rate at which producers acquire the chemical energy minus the rate at which they consume energy thru respiration
- NPP represents the biomass available to herbivores
Respiratory/Metabolic Rate (R): rate at which energy is consumed through respiration (and other metabolic activities needed for life)
- Most of energy is lost as heat
- Larger organisms = higher rate
- NPP = GPP – R
- Net Gain = energy storage or growth
- Net Loss = mass loss or death
Regulation of Primary Productivity
- Aquatic Biomes: Light and nutrients
- Terrestrial Biomes: Temperature and moisture
Light Limitation
- Solar energy exposure controls extent of photosynthesis and biomass of primary producers
Nutrient Limitation
- Limiting nutrient is the element that must be added for production to increase
- Usually nitrogen and phosphorous
- If a nutrient’s outputs exceed its inputs, that nutrient will eventually limit production in that ecosystem
- Adding more of the limiting nutrient will increase production until some other nutrient becomes limiting.
- Human impact example: fertilizer runoff adds nutrients and promotes growth of primary producers → primary producers die → bodies are broken down by aerobic decomposers. → depletes the water of much or all of its oxygen → kills large numbers of fish