• Chapter 55 – Ecosystems

Energy and Nutrient DynamicsEnergy and Nutrient Dynamics• Trophic structure / levels - feeding

relationships in an ecosystem• Primary producers - the trophic

level that supports all others; autotrophs

• Primary consumers - herbivores• Secondary and tertiary consumers

- carnivores• Detritivores/detritus - special

consumers that derive nutrition from non-living organic matter

• Food chain - trophic level food pathway

Energy FlowEnergy Flow• Primary productivity - amount of light energy converted to chemical

energy by autotrophs during a given time period, usually expressed as biomass– Gross (GPP): total energy– Net (NPP): represents the storage of energy available to consumers– R: respiration

• NPP = GPP - R• Biomass - primary productivity reflected as dry weight of organic

material

Energy TransferEnergy Transfer• Ecological efficiency - % of E

transferred from one trophic level to the next (5-20%)

• Secondary productivity - the rate at which an ecosystem's consumers convert chemical energy of the food they eat into their own new biomass

• Production efficiency (measure of energy transformation) = net secondary production / assimilation of primary production (portion of energy stored in food not used for respiration); basically the fraction of energy stored in food that is not used for respiration

• Birds and mammals have low production efficiencies = 1-3%

• Fish = 10%• Insects = 40% (see example)

Example: 33 J (approx. 1/6th) of plant is used for secondary production or growth. Has 33% production efficiency; 67 J of 100 J used for respiration

Ecological PyramidsEcological Pyramids• Trophic efficiency – percentage of

production transferred from one trophic level to the next

• Pyramid of net production – shows loss of energy from each trophic level

• Biomass pyramid – represents standing crop in each trophic level

• Pyramid of numbers• Green world hypothesis

Pyramid of numbers

Pyramid of net production

Biomass pyramid

Biogeochemical CyclesBiogeochemical Cycles

Biogeochemical Cycles (cont.)Biogeochemical Cycles (cont.)

Human Impact - NegativeHuman Impact - Negative• Nutrient enrichment

– Nitrogen contamination by agriculture– Eutrophication of aquatic ecosystems

• Acid precipitation – from burning of wood, coal, and other fossil fuels

• Toxins/Biological magnification– Humans dump toxins into environment– Tend to concentrate at higher trophic levels (example PCBs)

• Atmospheric CO2– as CO2 increases, global temperature increases; global warming

• Ozone Depletion– resulting from an accumulation of chlorofluorocarbons (CFCs)

from refrigeration units, aerosol cans, and manufacturing processes

• Rainforest Depletion

Human Impact - PositiveHuman Impact - Positive

• Restoration Ecology – goal to initiate or speed up the recovery of degraded ecosystems– Bioremediation: using organisms to detoxify

polluted ecosystems– Biological Augmentation: using organisms to

add essential materials to a degraded ecosystem