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Chapter 54

BIOLOGY 1M03 Chapter Notes - Chapter 54: Positive Feedback, Hubbard Brook Experimental Forest, Humus

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Jon Stone

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Biology Chapter 54: Ecosystems
An ecosystem consist of organisms that live in an area together with their
physical, or abiotic, environment
An ecosystem differs from a community because ecosystems are composed of
multiple communities along with their chemical and physical environments
Ex. A number of communities within a lake
oLake bottom, surface, shallow water
Adjacent ecosystems (river, lake, surrounding forest) can be distinguished
because their energy and nutrient flows are self-contained
Occasionally, energy and nutrients can also be transferred between ecosystems
Energy Flow and Trophic Structure
Ecosystems have four components
oThe abiotic environment
oPrimary producers
Four components are linked by a flow of energy
A primary producer is an autotroph, meaning an organism that can synthesize
its own food from inorganic sources
Most primary producers use solar energy to manufacture their own food via
In some ecosystems, bacteria use chemical energy contained in inorganic
compounds such as hydrogen, methane or hydrogen sulphide to make food
Primary producers form basis of ecosystems because they transform energy in
sunlight or inorganic compounds into chemical energy stored in sugars
Primary producers use this chemical energy in two ways
oMost supports maintenance or respiratory costs
oSome makes growth and reproduction possible

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Energy that is invested in new tissue is called net primary
productivity (NPP)
NPP represents amount of energy available to second and third
components of ecosystem, consumers and decomposers
Consumers eat living organisms
Herbivores are consumers that eat plants, carnivores eat animals, detritivores
or decomposers obtain energy by feeding on dead remains of other organisms
or waste products
Fourth component of an ecosystem is abiotic environment, which includes soil,
climate, atmosphere, Sun and particulate matter and solutes in water
Four components are linked because energy moves from Sun or inorganic
compounds to consumers, decomposers and abiotic environment
Understanding NPP is a primary focus of ecosystem ecology because it dictates
the amount of energy available to consumers and decomposers and because
global warming is altering NPP worldwide
Global Patterns in Productivity
oTerrestrial ecosystems with highest productivity are located in wet tropics
oWith exception of world’s major deserts, NPP on land declines from
equator toward the poles
oProductivity patterns in marine ecosystems are different
Marine productivity is highest along coastlines and can be as high
near the poles at it is in tropics
Oceanic zones have extremely low NPP
Among aquatic ecosystems, most productive habitats are algal
beds and coral reefs, wetlands and estuaries
Most of the total NPP provided by aquatic ecosystems derives from
open ocean, however
Even though NPP per square metre is low in these regions, open
ocean is so extensive that its total production is high
oWhat Limits Productivity
Data document that terrestrial productivity is lowest in deserts and
arctic regions

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This suggests that the overall productivity of terrestrial ecosystems
is limited by a combination of temperature and availability of water
and sunlight
To explain why productivity of marine habitats is higher along
coastlines than in deepwater regions, biologists focus on nutrient
Recall that neritic an intertidal zones along coasts receive nutrients
from two major sources
Rivers that carry and deposit nutrients from terrestrial
Nearshore ocean currents that bring nutrients from the cold,
deep water of oceanic zone back up to the surface
Both sources are absent in surface waters of open ocean
Also, nutrients found in organisms near surface of open ocean,
where sunlight is abundant, constantly fall to dark, deeper waters in
the form of dead cells and are lost
Analyses have found trace elements of zinc, iron and magnesium
are particularly rare in open ocean
Iron is essential to proteins involved in electron transport chains
Biologists have proposed that productivity of open-ocean
ecosystems could be increased dramatically by fertilizing them with
Experiments have shown that ocean waters naturally enriched by
nearby iron-containing rocks have exceptionally high NPP
Supports hypothesis that NPP in marine ecosystems is limited
primarily by availability of nutrients
How Does Energy Flow through an Ecosystem
oNPP productivity results in biomass, organic material that non-
photosynthetic organisms can eat
oChemical energy in primary producers eventually moves to primary
consumers or primary decomposers
oA primary consumer is a herbivore
Only a small percentage of all plant tissue is consumed by
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