Transcript Ch. 03 Introduction

• 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
Ecosystems
Chapter 3
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)
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
• Most producers are photosynthetic (e.g.
algae, mosses, diatoms, some bacteria,
plants etc.) but some are chemosynthetic
(e.g. hydrothermal vent bacteria)
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
• Role of consumers in an ecosystem is to
transfer energy from one trophic level to
the next
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
• Ecological Niche: A species' share of a
habitat and the resources in it.
– An organism's ecological niche depends not
only on where it lives but on the role it plays in
the ecosystem.
• Fundamental Niche: The part of the
habitat in which a species can live in the
absence of competitors and predators.
• Realized Niche: The part of the habitat
that the organism actually occupies.
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
• Energy flow through an ecosystem: An ecosystem’s trophic structure
determines energy flow and nutrient cycling.
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Producers
Herbivores
Carnivores
Decomposers
Nutrient Pool
Heat
• 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
• 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
– 1. MutualismInteraction between two species
where both benefit
– e.g. zooxanthellae in anemones & corals;
nitrogen fixing bacteria in legumes; cleaner
fish; lichen
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
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
Examples
• Bacteria in hydrothermal vent tubeworms
• Plasmodium falciparum (malaria-causing
protozoan) in Homo sapiens
Sea anemone and clownfish