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Primary Production and Energy Flow Chapter 18

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Primary Production and Energy Flow Chapter 18 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 23.
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