Lecture 17 Dynamics of Ecosystem Flashcards
Energy Flow
- 1st Law of Thermodynamics:
Energy cannot be created or
destroyed - Energy input must be continuous
for life to continue - Energy is converted to chemical
energy stored in food - 2nd Law of Thermodynamics:
Every exchange of energy increases
entropy - Energy conversion is inefficient:
some is lost as heat as it transfers
through ecosystems
slide 4
Nutrient Cycling
-Law of Conservation of Mass:
Matter cannot be created or
destroyed
* Nutrient inputs must equal
outputs
* Chemicals are continuously
recycled through the
ecosystem
* Energy passes through
ecosystems via trophic levels
which describe feeding
relationships
slide 5
Biogeochemical Cycles
slide 6
Biogeochemical Cycles: Water
- Water is essential to life!
- Availability limits primary production
and decomposition - Oceans contain 97% of water
slide 7
Biogeochemical Cycles: Nitrogen
- Nitrogen is an essential
component of amino acids,
proteins, & DNA - Plants can use ammonium
(NH4+) & nitrate (NO3-) - Animals can only use
organic forms of nitrogen
(amino acids) - 80% of the atmosphere is N2
gas - Nitrogen must be “fixed”
from N2 gas into usable
forms
slide 8
Biogeochemical Cycles: Phosphorus
- Phosphorus are a main component of nucleic
acids, phospholipids, and ATP - Phosphorus is used to build bones and teeth
- Plants absorb PO4
3- and synthesize into
organic compounds - Marine sedimentary rocks are the largest
reservoir - All organisms, ocean, and soil also contain
large amounts of Phosphorus - Phosphorus exchanges only on local scales
because there is no gas component of the cycle
slide 9
Biogeochemical Cycles: Carbon
- Carbon is used to form organic molecules &
store energy - Photosynthesizing organisms get carbon
from CO2 - Consumers get carbon from organic
molecules - Organisms return CO2 to the environment
when they respire and when they
decompose - Largest reservoir is sediments & rock
- All organisms are reservoirs of carbon
slide 10
Energy Budget: Primary Productivity
slide 11
Energy Budget: Primary Productivity
- Total amount of photosynthetic production sets
limits on ecosystems - Productivity is the rate that energy is converted
into biomass - Net Primary Production (NPP) is the amount of
stored energy available to consumers (new
biomass added) - Gross Primary Production (GPP) is the total
amount of energy converted to organic molecules
over time - Respiration by autotrophs (RA) is the amount of
energy used by photosynthesizing organisms
(~1/2 of GPP)
slide 12
Energy Budget: Ecosystem Productivity
-Net Ecosystem Production (NEP) is the amount of
biomass accumulated by producers & consumers
* Respiration by producers and consumers is the
amount of energy used by ALL organisms in the
ecosystem
* Carbon sinks have NEP > 0 (net storage of carbon)
Carbon sources have NEP < 0 (losing more carbon
than is being stored in plants and animals)
slide 13
Gross Primary Productivity
-Primary productivity varies
throughout the year!
* GPP does not account for energy
used by the ecosystem (can’t tell us if
it’s a carbon source or sink)
slide 14-15
Net Primary Productivity
slide 16
Primary Productivity Limitations
Limitations to photosynthesis in
aquatic systems:
* Light penetration
* Nutrient input (N and P)
* Micronutrients (minerals)
Limitations to photosynthesis in
terrestrial systems:
* Temperature
* Moisture
* Nutrients (N and P)
Upwelling brings
nutrients from deeper
water to the surface
Eutrophication occurs
when there is an
excess of nutrients,
causing explosive
growth of autotrophs
slide 17-19
Trophic Levels
slide 20
Trophic Levels:
Autotrophs
Autotrophs (primary producers)
use sunlight to synthesize sugars
and other organic compounds.
