Ecosystem Productivity • Three hundred trout are needed to support one man for a year. • The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons of grass.
Ecosystem Productivity • The amount of energy available in an ecosystem determines how much life it can support
Ecosystem Productivity • Gross primary productivity (GPP)- The total amount of solar energy that the producers in an ecosystem capture via photosynthesis over a given amount of time. • Net primary productivity (NPP)- The energy captured (GPP) minus the energy respired by producers.
Ecosystem Productivity • Gross Primary Productivity (GPP) • Total amount of energy that plants capture and assimilate in a given period of time • Net Primary Productivity (NPP) • Plant growth per unit area per time • Represents the rate at which organic material is actually incorporated into the plant tissue for growth • NPP= GPP - respiration • Only NPP is available as food to organisms • Units: kg c/m2/day or g/cm2/day
The Path of Energy Flow NPP= GPP - R
NPP Examples • Example: Two ecosystems Temperate forest: Primary producers = 1,500 g / m2 Desert: Primary producers = 100 g / m2 Food webs very complex, more tertiary consumers, some quaternary. Food webs very simple, very few tertiary consumers
Human Impact on NPP • Humans consume more of earth’s resources that any other animal • Humans represent 0.5% of land-based biomass • Humans use 32% of land-based NPP! • This may contribute to loss of species (extinction) • Humans’ high consumption represents a threat to planet’s ability to support both human and non-human inhabitants
SAMPLE NPP Calculation • NPP = GPP -R • %Efficiency = (output / input) x 100 • % Efficiency of Photosynthesis = (NPP / insolation energy) x 100. • 102 cm = 1m In a rice paddy in Southeast Asia the insolation energy is 6.0 x 106 cal/m2/day. The gross productivity of the rice is 0.012 g / cm2 /day and the respiration loss is 20%. One gram of rice is equal to 1000 calories. a.Calculate the net primary productivity of the rice. b.Find the efficiency of photosynthesis by the rice.
Energy Transfer Efficiency and Trophic Pyramids • Biomass- The energy in an ecosystem is measured in terms of biomass. • Standing crop- The amount of biomass present in an ecosystem at a particular time. • Ecological efficiency- The proportion of consumed energy that can be passed from one trophic level to another. • Trophic pyramid- The representation of the distribution of biomass among trophic levels.
Ecological Pyramids • Graphically represent the relative energy value of each trophic level • Important feature is that large amount of energy are lost between trophic levels to heat • Three main types • Pyramid of numbers • Pyramid of biomass • Pyramid of energy
Pyramid of Numbers • Illustrates the number of organisms at each trophic level • Usually, organisms at the base of the pyramid are more numerous • Fewer organisms occupy each successive level-WHY?
Pyramid of Biomass • Biomass: measure of the total amount of living material • Biomass indicates the amount of fixed energy at a given time
Pyramid of Energy • Illustrates how much energy is present at each trophic level and how much is transferred to the next level • Most energy dissipates between trophic levels • Explains why there are so few trophic levels • Energy levels get too low to support life • 10% RULE
Why the World Should Be Vegetarians That is 10 x more biomass available for (starving) humans
1 kg soybeans = 2.5 times calories 1 kg meat • 1 acre soybeans produces 25 times more calories when used for soy than beef production
13.5 kg coyote must range ~12 ha to subsist (30 acres). such as . . . Tertiary consumers must range over large areas to obtain enough energy to subsist. The Path of Energy Flow • Desert Biomass Pyramid Tertiary consumers = 0.1 g / m2 Secondary consumers = 1.0 g / m2 Primary consumers = 10 g / m2 Primary producers = 100 g / m2
The Path of Energy Flow 13.5 kg coyote only needs ~1 ha to subsist (2.5 acres). • Temperate Forest Biomass Pyramid Tertiary consumers = 1.5 g / m2 Secondary consumers = 15 g / m2 Primary consumers = 150 g / m2 Primary producers = 1,500 g / m2 Also, possibility of quaternary consumers, like bears.
Still Confused?Go to this Website and get more Confused! • http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/energyflow/energyflow.html