Ecosystems

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Ecosystems

• Chapter 25

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• What is the term used to describe the idea that
  the biosphere should be considered a single,
  living entity?
• The biotic portion of any ecosystem always
  consists of three types of organisms in the food
  chain. Name one of these three.
• This chapter describes four biogeochemical cycles
  involving four types of molecules. Name two of
  these.
• what is the term used to describe each individual
  level in a food chain?

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Chapter Overview

• Gaia- a hypothesis?
• What is an Ecosytem?
• Energy Flow and Its Impact on Ecosystems
• Recycling the Molecules of Life

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Gaia

• James E. Lovelock and Lynn Margulis
• The biosphere and the atmosphere, as well as the
  oceans and the soils, constitute a single immense
  entity-one that acts to preserve itself
• The personification of Gaia- she intervened and
  was impatient

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Is an Ecosystem a Single, Living System?

• An ecosystem has many of the properties of a
  living organism that we listed in Chapter 1. An
  ecosystem obtains energy from its environment,
  transforms chemicals, changes with time, and
  responds to environmental changes. And
  ecosystems, like individual organisms, use energy
  to maintain a stable state.

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What is Ecology?

• Population
• Community
• Ecosystem
• biotic
• abiotic

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Defining an Ecosystem

• Arbitrary
• Hierarchical
• The Biosphere

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Three Types of Living Creatures in an Ecosystem

• Producers
• harvest energy directly from sunlight or
  inorganic molecules
• Consumers
• obtain energy by eating producers or other
  consumers herbivores, carnivores, and omnivores
• Decomposers
• obtain energy by taking in organic compounds from
  dead organisms

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Describing an Ecosystem

• How many different species of organisms are
  present?
• Who is eating who?
• What is the biomass of organisms at different
  trophic levels?
• What abiotic factors determine the number of
  species and the food web that exists?

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A Pyramid of Biomass
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Biomass in Aquatic Ecosystems
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Important Principles in Energy Flow in Ecosystems

• Total Chemical Energy production over time in
  producers always exceeds that produced by
  consumers over the same period
• Energy is lost as heat when flowing from low
  trophic levels to high ones

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Energy Flow In Ecosystems

• 1-2 million kcal of light energy strikes a square
  meter of land in a year
• Plants Convert about 1-5 into chemical energy
• Plant use about 40 of this 1-5 for building
  macromolecules
• Only 20 of this may be consumed by primary
  consumers

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Productivity Pyramids

• What is productivity of a trophic level?
• the energy captured in the new chemical bonds of
  molecules each year per square meter
• Do you expect the productivity levels to be the
  same in various ecosystems?

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See Table 25-1
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Four Biogeochemical Cycles

• Water
• Carbon
• Nitrogen
• Phosphorus

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Why is Water so Important?
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The Phosphorus Cycle

• Water in the soil contains about 0.000003 percent
  usable phosphorus
• Plants can use orthophosphate (H2PO4-) or
  phosphate ion PO43-, which is formed when
  orthophosphate is dissolved in water
• Many plants are aided by Mycorrhizae in taking up
  phosphate