Transcript Community Ecology - Gustavus Adolphus College

Communities + physical processes interconnect to
form ecosystems
Ecosystems are connected by:
1. energy flow between trophic levels; energy also released
as heat energy into environment
• Autotrophs = 10 producers
– Primary productivity = amount of C fixed in an ecosystem by: CO2 +
H20 + light --> (C6H1206) + O2
• Heterotrophs
– Consumers: herbivores, omnivores, carnivores
– Decomposers
2. Nutrient and water cycling (Biogeochemical cycling)
1. water, 2. carbon, 3. nitrogen, 4. phosphorus
Humans have impacts on ecosystems
Energy flow (also refer to Fig. 20.3 & 20.7)
• Only ~10 % transfers between levels.
• Loss due to: Metabolism and waste
BioGeoChemical cycles = Nutrients cycle btwn biotic & abiotic forms
Definitions of: Reservoirs and fluxes, mineralization, fixation/assimilation
Flux rate dependent on ?
Major Biogeochemical cycles: Atmospheric cycles = carbon and nitrogen; Sedimentary =
phosphorus; Hydrologic
9
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Carbon
• Reservoirs = ?
• Transformations?
Nitrogen
- why is N impt?
- what is symbiotic N fixation?
- cause and results of excess N?
N2
Nitrogen fixation
Dead organisms
Rhizobium
Decomposition
Fungi, bacteria, inverts
Plants
Organic matter
Mineralization
Assimilation
Denitrification
Anaerobic
bacteria
Fungi, bacteria
NH4+
NO2-
NO3-
ammonium
nitrite
nitrate
Industrial inputs:
Fertilizer, atmospheric deposition
Phosphorus
Pools? Transformations?
Cause and consequences of excess P in aquatic systems
–PO4- is difficult to acquire
–80 % of plants have mycorrhizal symbionts to
help (fungi); other benefits (+H20) offset cost
• Biotic factors increase nutrient retention – how?
• Excessive disturbance decreases retention – why?
Human Impact 1
• Reduced biodiversity, habitat loss, habitat
fragmentation
Human Impact 2
• Pollution: air, water, land
• Reduction in ozone layer
Human Impact 3 - Excess N & P
Monthly average carbon dioxide concentration in atmosphere
Mauna Loa, HI
360
350
CO2 (parts per million)
Human Impact 4 - Accelerated release
of CO2
340
330
320
310
1950
1960
1970
1980
Year
1990
2000