BSC 2011 Lecture 9: 9 Ecosystems 1

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Biology - Biological Sciences
BSC 2011
Jennie Demarco

9 Ecosystems 1 Monday, April 10, 201710:39 AM Ecosystems • Energy flow ○ Assimilation efficiency increases at higher trophic levels ○ Net production efficiencies decrease at higher trophic levels ○ Ecological efficiencies average about 10 % ○ Only 1% of NPP ends up as production in the 3rd trophic level • NPP in terrestrial systems is often limited by climatic factors ○ Temp increases so does NPP ○ NPP increases with increasing precipitation to about 2400mm, then decreases at higher levels § If its raining a lot, there is not a lot of sun, less light availability, less photosynthesis § Less O2 • Plant resources control NPP ○ Light ○ Temp ○ Water ○ CO2 ○ Nutrients ○ Controls photosynthesis also controls NPP • Controls on NPP ○ NPP in terrestrial systems may also be limited by nutrients ○ NPP in aquatic systems in often limited by light and nutrients ○ Nitrogen and phosphorus § 1-4% N in leaves § .1-.4% P in leaves • Elements cycling in ecosystems ○ There is continual recycling between the organisms an the physical environment ○ Nutrients unlike energy are retained within the ecosystem Organisms-biosphere ○ ○ Air- atmosphere ○ Lithospher-land ○ Hydrosphere-water environment ○ Nutrients unlike energy are retained within the ecosystem
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