2.3: Flows of Energy and Matter

significant ideas

1) the interactions of species with their environment result in energy and nutrient flows

2) photosynthesis and respiration play a significant role in the flow of energy in communities

3) the feeding relationships of species in a system can be modeled using food chains, food webs and ecological pyramids

fate of solar radiation

percentage of sun’s radiation available for plants during photosynthesis

1%

albedo

reflectivity of a surface (dark colors = low, light colors = high)

productivity

conversion of energy into biomass over a given period of time (rate of growth or biomass increase in plants and animals)

measured by: UNIT J/m^-2 YR^-1 or G m ^-2 YR^-1

types of productivity

primary: productivity of autotrophs

secondary: productivity of heterotrophs

gross primary productivity (GPP)

total gain in energy or biomass per unit area per time by green plants (biomass that could be gained before deductions)

net primary productivity (NPP)

gain in energy or biomass (per unit area per time) that remains after deduction due to respiration → what is available for consumers to eat

NPP = GPP - R

J/m^-2/yr

respiration

amount of biomass consumed during cellular respiration to keep the producer alive → lost and is not passed to next trophic level

how does biomass vary

• spatially (latitude) - near equator more consistent biomass

• temporally (seasons) - further from equator, season influences increase and decrease in biomass

gross secondary productivity (GSP)

total energy/biomass assimilated by consumers

GSP = food eaten - fecal loss

J

net secondary productivity (NSP)

total gain in energy/biomass per unit are per unit time by consumers after allowing for losses to respiration

NSP = GSP - R

* growth because it is what is left after other life processes have taken place

J/m^-2/yr^-1

primary vs secondary productivity

plants vs consumers

diff equations

primary productivity accounts for respiration, secondary for fecal loss in gross productivity and respiration for net productivity

methods for measuring primary productivity

1. harvest method - measures biomass and expresses biomass per unit area per unit time

2. CO2 assimilation - measures CO2 uptake in photosynthesis and released by respiration

3. O2 production - measure O2 production and consumption

4. radioisotope method - use C14 tracer in photosynthesis

5. chlorophyll measurement - assumes a correlation between the amount of chlorophyll and the rate of photosynthesis

energy flow through ecosystems

2 ways ecological efficiency can be calculated

* efficiency of transfer from trophic level to the next is 10%

• efficiency of assimilation = (gross productivity/food eaten) x 100

• efficiency of biomass = (net productivity/gross productivity) x 100

sustainable yield

amount of biomass that can be extracted without reducing natural capital (stock of renewable and non-renewable resources that combine to yield a flow of benefits to people) of the system

maximum sustainable yield

amount of biomass which may be removed from an ecosystem without diminishing the natural income produced by that system each year

• transfer b/c matter moves from place to place

• must not exceed the income so that capital remains same

• eg: cutting trees, hunting, fishing, etc

study 12 on 2.3 notes

energy

flows directly through earth’s ecosystems (mostly as sunlight, exits as heat)

travels through food chains and lost as heat

matter

gets recycled through biogeochemical cyces

moves between stores (sinks)

* nutrients and matter are finite

carbon cycle

• regulates climate through amount of carbon in atmosphere

• when fossil fuels are burned carbon is transferred out of stores and into the atmosphere → affects climate

• fires and other disasters that occur from deforestation and climate change add CO2 to atmosphere (but also lets some environments recover)

nitrogen cycle

most abundant gas in the atmosphere (but in an unavailable form)

1. nitrogen fixation

2. nitrification

3. denitrification

effects of commercial agriculture: increases air pollution and acid rain, uses inorganic fertilizers, livestock release ammonia, wetland denitrification is reduced so less nitrogen enters atmosphere → fosters environment for weeds, eutrification, altered food web, etc

how does removing biomass relate to growing crops, raising livestock, and harvesting wild animals

this removes food or habitat for native species present, affecting those at top of food chain who have a harder time making up the energy deficit