Chapter 54 ~ Ecosystems

Relationships, I

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

Detrivores/detritus ~ special consumers that derive nutrition from non-living organic matter

Food chain ~ trophic level food pathway

Relationships, II

Food webs ~ interconnected feeding relationship in an ecosystem

Energy Flow, I

Primary productivity (amount of light energy converted to chemical energy by autotrophs) •Gross (GPP): total energy •Net (NPP): represents the storage of energy available to consumers •Rs: respiration

NPP = GPP - Rs

Biomass: primary productivity reflected as dry weight of organic material

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

Energy Flow, II

Ecological efficiency : % of E transferred from one trophic level to the next (5-20%)

Pyramid of productivity : multiplicative loss of energy in trophic levels

Biomass pyramid : trophic representation of biomass in ecosystems

Pyramid of numbers : trophic representation of the number of organisms in an ecosystem

Chemical Cycling

Biogeochemical cycles: the various nutrient circuits, which involve both abiotic and biotic components of an ecosystem

Water

Carbon

Nitrogen

Phosphorus

Water Cycle

cycles as H 2O

Precipitation

Evaporation

Condensation

Transpiration

Percolation

Run-off and groundwater

Nitrogen Cycle

cycles as N 2 and in various compounds

N 2 reservoir in atmosphere

Nitrogen fixation (N 2 à NH 4 +)

Rhizobium (symb), Azotobactor(free)

Ammonification (decp à NH 4 +)

Nitrification (NH 4 + à NO 2 -)

Nitrosomonas

Nitrification (NO 2 - à NO 3 -)

Nitrobacter

Denitrification (NO 2 - à N 2) and (NO 3 - à N 2)

Pseudomonas

Assimilation (to plant tissue)

Carbon Cycle

Cycles as CO 2 and in organic compounds

CO 2 in atmosphere

Photosynthesis

Cellular Respiration

Decomposition

Detritus

Burning of wood and fossil fuels

Photosynthesis:

6CO 2 + 6H 20 à C 6H 12O 6 + 6O 2

Cellular Respiration

C 6H 12O 6 + 6O 2

PHOSPHORUS CYCLE

Cycles as a mineral in soil, water, and organisms

Human Impact

Biological magnification : trophic process in which retained substances become more concentrated at higher levels

Greenhouse effect : warming of planet due to atmospheric accumulation of carbon dioxide

Ozone depletion : effect of chlorofluorocarbons (CFC’s) released into the atmosphere

Rainforest destruction

Cause: Overpopulation?

Ozone Depletion

Low altitudes: 0.01 ppm

Stratosphere: 1 – 10 ppm

Absorbs short wave radiation (UV)

UV radiation increases mutation rates

Causes cancer, sunburn, cataracts

Reduces photosynthesis rates in plants

Depletion is hastened by CFC’s

Ozone and CFC’s

CFC = chloroflorocarbons

Used as refrigerants, aerosol cans (propellant), gas-blown plastics (styrofoam)

CFC’s react with UV radiation and release chlorine atoms.

Chlorine reacts with ozone and converts it to O 2

Chlorine is released to react with more ozone

Montreal Protocol (1987) calls for:

Replacing CFC’s with other chemicals

Collecting old refrigerants from discards

Levels should start to fall by 2010/ozone should be replaced by 2050

Acid Rain

Gases (carbon dioxide, sulfur dioxide, nitrogen oxides) dissolve in droplets of water and make precipitation acidic (sulfuric acid and nitric acid)

Sulfur dioxide and nitrogen oxides are primarily produced by man.

pH of rain can get as low as pH3.

Droplets can travel long distances

Mountain lakes affected quickly b/c they are shallow and don’t have limestone (Calcium carbonate) to buffer the acid.

Acid Rain Consequences

Aluminum is dissolved by the acid and leaches into lakes and streams. Al ions are toxic to fish.

K +, Mg +2, Ca +2 leach out of acidic soil, making soil less fertile.

Trees show premature leaf fall and dieback of branches. (Conifers are the most vulnerable.)