Lecture 8. Ecosystems

Updated: 1/15/08

Thursday, April 17, 2008. Reading: 37.9-37.20

Ecosystems

Ecosystems include the biological community and abiotic resources. Two fundamental processes in ecosystems are
- energy flow: energy comes from an outside source, flows one way through various components of an ecosystem and is then lost
- chemical cycling: materials pass through biotic and abiotic reservoirs, often changing form and availability to other reservoirs
Trophic structure

Trophic structure determines energy flow, and is a key factor in ecosystem dynamics.
- the food chain is an abstract grouping of organisms in an ecosystem based on tropic level (producers, primary and secondary consumers, detritivores). In reality, food chains interconnect to form food webs, and the variety of links stabilize ecosystems
- primary production and rates of transfer differ among ecosystems and limit the length and complexity of food webs
Major nutrient cycles

for each cycle, you should know the important reservoirs, links between them and which links are one-way versus-two way. These four cycles are among the most important because they concern the major materials required by plants for photosynthesis.
- WATER
- CARBON
- NITROGEN
- PHOSPHOROUS

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