Energy flow & primary productivity
- Primary producers (usually plants and other photosynthesizers) are the gateway for energy to enter food webs.
- Productivity is the rate at which energy is added to the bodies of a group of organisms (such as primary producers) in the form of biomass.
- Gross productivity is the overall rate of energy capture. Net productivity is lower, adjusted for energy used by organisms in respiration/metabolism.
- Energy transfer between trophic levels is inefficient. Only of the net productivity of one level ends up as net productivity at the next level.
- Ecological pyramids are visual representations of energy flow, biomass accumulation, and number of individuals at different trophic levels.
Producers are the energy gateway
- Gross primary productivity, or GPP, is the rate at which solar energy is captured in sugar molecules during photosynthesis (energy captured per unit area per unit time). Producers such as plants use some of this energy for metabolism/cellular respiration and some for growth (building tissues).
- Net primary productivity, or NPP, is gross primary productivity minus the rate of energy loss to metabolism and maintenance. In other words, it's the rate at which energy is stored as biomass by plants or other primary producers and made available to the consumers in the ecosystem.
How does energy move between trophic levels?
- Primary producers, such as plants and algae:
- Primary consumers, such as snails and insect larvae:
- Secondary consumers, such as fish and large insects:
- Tertiary consumers, such as large fish and snakes: