Chapter 56

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Biological Science
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1

Learning objectives

  • Describe how energy is transferred in an ecosystem and contrast that to nutrient transfer
  • Explain how pollutants are concentrated at higher trophic levels
  • Describe how humans have altered global biogeochemical cycles (esp. carbon)
2

Ecosystems

  • Communities of organisms + abiotic components
  • The biotic and abiotic components of an ecosystem are linked by flows of energy and nutrients
3

Energy flow through ecosystems

Primary production transforms the energy in sunlight or inorganic compounds into chemical energy (stored in sugars) and use this energy for maintenance (respiration) and growth & reproduction (adding tissue)

4

Gross primary productivity (GPP)

The total amount of chemical energy (sugar) produced in a given area and time period

5

Net primary productivity (NPP)

  • Energy used for growth = biomass
  • This is the energy available for other organisms
6

How Efficient Are Autotrophs at Capturing Solar Energy?

  • 0.8%
  • Why so inefficient?
    • Photopigments
    • Photosynthesis reduced in winter and dry conditions
    • Enzyme efficiency varies with temperature
7

What Happens to the Biomass of Autotrophs?

  • Consumers eat living organisms
    • Primary consumers eat primary producers
    • Secondary consumers eat primary consumers
    • Tertiary consumers eat secondary consumers
  • Decomposers (detritivores) feed on detritus, the waste products or dead remains of other organisms
  • Components linked by the movement of energy and nutrients
8

Nutrients cycle through ecosystems

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9

Food chain

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A food chain connects trophic levels

– Describes how energy moves from one trophic level to another

– Decomposer food chain begins with dead stuff

– Grazing food chain begins with live primary producers

10

Food webs

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11

Productivity (biomass) pyramid

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The “10% rule”: Only 10% of the energy stored as biomass at one trophic level can be stored as biomass in the next trophic level.

12

Tuna sandwich

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13

Biomagnification

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Increase in concentration of certain molecules (esp. persistent organic pollutants) up the food chain

14

Bigeochemical cycles

Circulation of chemical nutrients like carbon, oxygen, nitrogen, water through the biological and physical world.

15

Global carbon cycle

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  • Global carbon cycle
    • Movement of carbon among three (four) “reservoirs”
    • terrestrial ecosystems, oceans, atmosphere, (fossil fuels)
  • OCEAN = largest reservoir
  • Photosynthesis takes carbon from atmosphere into tissue
  • Respiration releases carbon from tissue into atmosphere
16

Threats to biodiversity

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  • Species are vanishing faster than at virtually any other time in Earth’s history
    • Modern rates of extinction are 100 to 1000 times greater than the average, or “background,” rate
17

Habitat destruction

– Logging and burning, Grazing livestock, Development

• At current rate, lose 28% wet tropical forest in your lifetime

• Wet tropical forest = biodiversity “hotspots”

18

Habitat degredation

Habitat fragmentation

• Some fragments too small for some species

• Reduces dispersal & population sizes

• Creates edge habitat

• -> DRAMATIC LOSS OF DIVERSITY & BIOMASS

19

Overxploitation

  • Unsustainable removal of wildlife for human use
    • Overhunting (esp. marine species), pet trade
20

Invasive species

Nonnative species disrupting native species

21

Why is biodiversity important

  • Biodiversity has both economic and biological benefits.
  • Greater biodiversity is associated with
    • Greater NPP
  • More primary biomass brings more energy to ecosystem
    • Greater stability
  • Resistance, resilience
  • Ecosystem services
    • Pollination, filtration, decomposition
22

Biophilia

The urge to affiliate with other forms of life.