Ecosystem Ecology

Raymond Lindeman Sir Arthur Tansley

Some Energy Flow Definitions

• Gross primary production (GPP) - total fixation of energy by autotrophs - usually just due to photosynthesis, primarily by plants

• Net primary production (NPP) = GPP - respiration, autotrophs use some energy for their own growth and that is lost as respiratory heat, so NPP represents what is available to heterotrophs - NPP is often 10% of GPP

• Secondary productivity - production of biomass by heterotrophs

• Standing crop - amount of biomass of living organisms in a unit of area

P – productivity tn/ha/yr; B – biomass tn/ha; R - solar radiation – kcal/m2/yr

Temperature, Precipitation and Productivity

Limits to Terrestrial Productivity

a) shortage of water restricts rate of photosynthesis

b) shortage of mineral nutrients slows down rate of production of photosynthetic tissue and the effectiveness of photosynthesis

c) temperatures that are lethal or too low for growth

d) insufficient depth of soil (deserts, mountain tops)

e) incomplete vegetation canopy cover so that much sunlight lands on the ground and not on foliage

Comparison of productivity by a deciduous tree and an evergreen tree

Limits to Aquatic Productivity

a) Lack of nutrients

b) Light is limiting – suspended particles in water reduce light penetration

c) Intensity of grazing

Coastal Upwelling

Light Penetration in Oceanic Waters

Basic ecosystem - nutrient cycling in red, energy flow in grey

Basic Energy Flow

Basic Energy Flow

Energy Flow Expanded

Energy Flow in Different Ecosystems

Transfer Efficiency

10% Rule for Transfer Efficiency

Consumption Efficiency• CE = food ingested/food produced

• How much of prey population that consumer eats

• For herbivores – 5% in forests, 25% in grasslands, 50% in phytoplankton ecosystems

• For vertebrate predators – up to 50-100% vertebrate prey; 5% invertebrate prey

• For invertebrate predators – 25% invertebrate prey

Assimilation Efficiency

• AE = food assimilated/food ingested

• How much of prey eaten is digested

• AE usually low for herbivores, microbivores, detritivores – 20-50%

• AE usually high for carnivores – 80%

Production Efficiency

• PE = new biomass produced/food assimilated

• How much of prey digested is converted to consumer biomass and used in reproduction – rest is lost as respiratory heat

• PE high for invertebrates – 30-40%

• Intermediate for ectotherm vertebrates – 10-20%

• Low for endotherm vertebrates – 1-2%

Lindeman’s Efficiency

• LE = assimilation at trophic level n

assimilation at trophic level n – 1

LE examines efficiency of transfer between trophic levels – often assumed to be 10% but…is actually more complex

Light Absorption

Lindeman’s Efficiencies