They consume other organisms for food

They fix carbon using external energy sources

They obtain energy by consuming organic compounds but do not fix carbon

They fix carbon but use organic compounds as their energy source

Photosynthesis by algae living near hydrothermal vents

CO2 fixed using energy from oxidizing inorganic compounds

External input of organic carbon from photic-zone ecosystems

Respiration rates higher than carbon fixation rates

Primary occurs in decomposers, secondary in autotrophs

Primary is accumulation by autotrophs, secondary by heterotrophs

Primary involves respiration, secondary does not

Both only occur in aquatic ecosystems

More energy is stored at each higher trophic level

Only producers use energy

Energy is lost at each level through respiration and heat

Primary consumers are always more abundant than producers

Respiration and heat loss limit usable energy at each trophic level

Organisms avoid predation by hiding in dense foliage

Only a small fraction of biomass is transferred to the next trophic level

Decomposers remove available energy before it moves up