Primary Production and Energy Flow Chapter 18

Sunlight to photosynthesizer to herbivore to carnivore to decomposer!!!

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ecosystem Ecology • The study of the flow of energy, water, and nutrients in an ecosystem  An ecosystem is a biological community + all the abiotic factors that influence that community!

2 Introduction – some terms! • Primary production: Fixation of energy by autotrophs in an ecosystem.  Rate of primary production: Amount of energy fixed over a given period of time. . Gross primary production: Total amount of energy fixed by autotrophs. . Net primary production: Amount of energy leftover after autotrophs have met their metabolic needs.

3 Introduction – some more terms!!!

• Trophic Level: Position in a food web determined by number of energy transfers from primary producers to current level:  Primary producers occupy first level.  Primary consumers occupy second level.  Secondary consumers occupy third level.  Tertiary consumers occupy fourth level. http://www.youtube.com/watch? v=fwqF5ouTyT0 4 Patterns of Terrestrial Primary Production • Terrestrial primary production is generally limited by temperature and moisture.  Highest levels of primary production – warm & moist

5 Actual Evapotranspiration and Terrestrial Primary Production - Ecosystems • Generally, there is a positive relationship between net primary production and AET.

Annual actual evapotranspiration (AET). •Annual amount of water that evaporates and transpires off a landscape. •Cold dry ecosystems tend to have low AET. Warm & moist have high AET 6 What about primary production within one ecosystem?

7 Other Factors in Terrestrial Primary Production: Soil Fertility • Significant variation in terrestrial primary production can be explained by differences in soil fertility.

8 Patterns of Aquatic Primary Production

• Aquatic primary production is generally limited by nutrient availability • What don’t aquatic ecosystems need to worry about at all???

9 Patterns of Aquatic Primary Production

Several studies have found a relationship between phosphorus and phytoplankton biomass.

More phosphorus (nutrient) = more phytoplankton = more primary production

10 Need more proof???

Booyah!!!

11 Global Patterns of Marine Primary Production • Highest rates of primary production by marine phytoplankton = highest nutrients • Highest rates @ upwelling regions, continental margins  Nutrient run-off from land & sediment disturbance • Open ocean tends to be nutrient poor.  Vertical mixing main nutrient source.

12 Global Patterns of Marine Primary Production

There are other More proof! factors besides Booyah!!! nutrients like…???

Predation!

13 Consumer Influences on an ecosystem • Bottom-Up Controls  Influences of physical and chemical factors of an ecosystem (already discussed – nutrients, precipitation, etc.) • Top-Down Controls  Influences of consumers. Consumers can influence rates of primary production in aquatic and terrestrial ecosystems through trophic cascades

14 What exactly is a trophic cascade??? • Involves effects of predators on prey that alter abundance, biomass, or productivity of a population, community, or trophic level across more than one link in the food web Planktivorous fish get Piscovore eaten=they lose! biomass has an indirect Large zooplankton cascading gain =phytoplankton effect on lose! populations http://www.youtu besides be.com/watch? planktivorous fish v=O8BV0VCn1JU 15 16 Consumer Effects: Primary Production on the Serengeti  Rate of primary production in the Serengeti is positively correlated with rainfall quantity. . Makes sense, right! What doesn’t make sense: Found grazers can increase primary production???!!! What’s going on???

17 Consumer Effects: Primary Production in the Serengeti

•Increased growth rate in grazed areas!!! •Compensatory Growth •Lower respiration rate due to lower biomass. •Reduced self-shading. •Improved water balance due to reduced leaf area 18 Consumer Effects: Primary Production in the Serengeti • In addition, compensatory growth highest at intermediate grazing intensities.  Light grazing insufficient to produce compensatory growth.  Heavy grazing reduces plant’s capacity to recover. An example of a trophic cascade. Why?

What would predation of wildebeests do???

19 Trophic Levels • Ecosystems have a limited number of trophic levels  What limits them??? • As energy is transferred from one trophic level to another, energy is degraded. . Limited assimilation . Consumer respiration . Heat production  Ecological Efficiency is the percentage of energy transferred from one trophic

level to the one above it 20 Trophic Dynamic View of Ecosystems

 Pyramid-shaped energy distribution.

21 Energy Flow in a Temperate Deciduous Forest

• Gosz studied solar energy flow:  15% reflected  41% converted to heat  42% absorbed during evapotranspiration  2.2% fixed by plants as gross primary production  1.2% used in plant respiration  1% left for primary production

22 Energy Flow in a Temperate Deciduous Forest • 99% of solar energy unavailable for use by second trophic level. • As energy losses between trophic levels accumulate, eventually there is insufficient energy left to support a viable population at a higher trophic level.

http://www.youtub e.com/watch? v=BVJ4-q7bXjw

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