Topic 2 The Ecosystem

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Topic 2 - The Ecosystem

• Syllabus Topics 2.1.1-2.1.3, 2.1.10, 2.2.1,
  2.2.3
• Reading
• Environmental Science (Wright and Nebel, 8th
  edition) pp. 23-40
• Biology (Campbell) pp. 1131-1134 (ecosystems)
  1109-1114 (symbioses)

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Topic 2 The Ecosystem

• Ecosystem - a community of interdependent
  organisms and the physical environment they
  inhabit (IB)
• Biotic abiotic components of ecosystems
• Biotic factor - a living, biological factor that
  may influence an organism or an ecosystem (IB)
• e.g. predation, disease, competition
• Abiotic factor - a non-living, physical factor
  that may influence an organism or an ecosystem
  (IB)
• e.g. temperature, salinity, pH, light

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Ecosystem structure

• Often described based on feeding relationships
• Species can be divided into trophic levels based
  on their main source of nutrition
• Trophic level - the position that an organism
  occupies in a food chain OR a group of organisms
  in the community that occupy the same position in
  food chains
• The trophic level that ultimately supports all
  others consists of autotrophs (primary producers)

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Producer

• Autotroph - self feed
• An organism that obtains organic food molecules
  without eating other organisms but by using
  energy from the sun or inorganic molecules to
  make organic molecules
• Remember this trophic level supports all others
• Role of producers is to convert energy into a
  form useable for other organisms

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• Most producers are photosynthetic (e.g. algae,
  mosses, diatoms, some bacteria, plants etc.) but
  some are chemosynthetic (e.g. hydrothermal vent
  bacteria)

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Consumer

• Heterotroph - other feed
• An organism that obtains its nutrition by eating
  other organisms
• Primary consumer (herbivore) - eats producers
  e.g. sea urchin, copepod
• Secondary consumer (carnivore) - eats primary
  consumers e.g. wolf eel, herring
• Tertiary consumer - eats secondary consumers e.g.
  sea otter, seal
• Quaternary consumer - eats tertiary consumers
  e.g. killer whale

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• Role of consumers in an ecosystem is to transfer
  energy from one trophic level to the next

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Decomposer

• An organism that obtains energy by breaking down
  dead organic matter (including dead plants, dead
  animals and animal waste) into more simple
  substances
• e.g. bacteria and fungi
• Interconnect all trophic levels since the organic
  material making up all living organisms is
  eventually broken down
• Role of decomposers is to return valuable
  nutrients to the system so they can be used again

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Ecological Niche
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Food chains and food webs

• Few systems are so simple that they just consist
  of an unbranched food chain
• Most are very complex as many species feed on
  more than one species and some consumers even
  feed at different trophic levels resulting in a
  food web
• Food webs are more complex and therefore more
  stable

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Energy flow through an ecosystem

• An ecosystems trophic structure determines
  energy flow and nutrient cycling

Producers
Herbivores
Carnivores
Decomposers
Nutrient Pool
Heat
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Laws of thermodynamics

• Remember them?
• How do they apply to ecosystems?
• First law - Energy is transferred from one
  trophic level to the next, energy is transformed
  from light to chemical (photosynthesis) and
  chemical to heat (respiration)
• Second law - as energy flows through an
  ecosystem, much of it is lost at each trophic
  level

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Rainbow trout in Northern Pike
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Symbiosis

• sym together, bio life
• Relationship between two organisms that is not
  necessarily based on feeding
• An ecological relationship between organisms of
  two different species that live together in
  direct contact
• 3 types of symbiosis - mutualism, commensalism,
  parasitism

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1. Mutualism

• Interaction between two species where both
  benefit
• e.g. zooxanthellae in anemones corals nitrogen
  fixing bacteria in legumes cleaner fish lichen

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2. Commensalism

• Interaction between two organisms in which one
  species benefits while the other is unaffected
• e.g. eyelash mites, orchids as epiphytes, remora
  on shark

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3. Parasitism

• Interaction where one organism benefits while the
  other is harmed
• e.g. tapeworm in human digestive system leeches
  on fish fleas on a dog sea lettuce growing on
  bull kelp

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Other symbiosis examples

• Barnacles on whales

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More examples

• Bacteria in hydrothermal vent tubeworms
• Plasmodium falciparum (malaria-causing protozoan)
  in Homo sapiens
• Sea anemone and clownfish