1,000,000 J of sunlight
In a biomass pyramid, each tier represents the dry weight of all organisms in one trophic level.
Most biomass pyramids show a sharp decrease at successively higher trophic levels
Certain aquatic ecosystems have inverted biomass pyramids: producers (phytoplankton) are consumed so quickly that they are outweighed by primary consumers.
Turnover time is a ratio of the standing crop biomass to production.
Pyramids of biomass = standing crop:
(a) Most ecosystems (data from a Florida bog)
Primary producers (phytoplankton)
(b) Some aquatic ecosystems (data from the English Channel)
Primary consumers (zooplankton)
Dynamics of energy flow in ecosystems have important implications for the human population.
Eating meat is a relatively inefficient way of tapping photosynthetic production.
Worldwide agriculture could feed many more people if humans ate only plant material.
Most terrestrial ecosystems have large standing crops despite the large numbers of herbivores.
The green world hypothesis proposes several factors that keep herbivores in check:
Limited availability of essential nutrients
Life depends on recycling chemical elements.
Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles.
Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally.
Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level.
A model of nutrient cycling includes main reservoirs of elements and processes that transfer elements between reservoirs.