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Visualizing Physical Geography
by Alan Strahler and Zeeya Merali
Chapter 16
Biogeographic Processes
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Energy and Matter Flow in Ecosystems
Biogeography: the study of the distribution patterns of organisms over
space and time and of the processes that produced these patterns
Ecosystem?
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Energy and Matter Flow in Ecosystems
The Food Web
Food web (food chain): organization of an
ecosystem into levels through which
energy flows as the organisms at each
level consume energy from the bodies of
organisms in the level below
• Primary producers: ?
• Consumers: ?
•
•
•
•
Decomposers: ?
Energy is lost at each level in food web by respiration
Only 10 to 50% of the energy stored at one level passes up to the next level
Normally, about 4 levels of consumers
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Food Web
Energy and Matter Flow in Ecosystems
Photosynthesis and Respiration
Photosynthesis: production of carbohydrate from water and
carbon dioxide, using light energy
H20 + CO2 +light energy
CHOH
+ O2
Rates of
photosynthesis
depend on light
intensity,
duration of
daylight, and
temperature
Energy and Matter Flow in Ecosystems
Photosynthesis and Respiration
Respiration: carbohydrate is broken down and combines
with oxygen to yield carbon dioxide and water, releasing
energy
CHOH
+ O2
CO2 + H2O + chemical energy
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Energy and Matter Flow in Ecosystems
Net Primary Production
Net primary production: annual yield of useful energy produced by the
ecosystem, in grams/square meter/year
Biomass: dry weight of living organic matter in an ecosystem within a
designated surface area (grams/square meter or metric tons/hectare
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Carbon cycle: biogeochemical cycle
in which carbon moves through the
biosphere
The Nitrogen Cycle
Ecological Biogeography
Ecological biogeography examines the distribution patterns of
plants and animals from the viewpoint of their physiological
needs
Habitat: subdivision of
the environment
according to the needs
and preferences of
organisms or groups of
organisms
Ecological niche: ?
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Water Need
Xerophyte: plant adapted to dry conditions
• Phreatophytes: plants that obtain water from ground water
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Water Need
Some climates have yearly wet and dry seasons: wet-dry tropical
climate, moist continental climate, Mediterranean climate
Tropophyte: plant adapted to changing conditions/dry season
alternating with wet season
• Deciduous: plants that drop their leaves
seasonally
• Evergreens: plants that keep most of their
leaves more than 1 year
• Mediterranean climate plants often
xerophytic, evergreen, with hard, leathery
leaves (sclerophylls)
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Water Need
Xeric animals:
• Many invertebrates dormant during dry
periods
• Many birds only nest when rains occur
• Many desert animals active only at night,
stay in burrows in the day
• Many desert mammals do not sweat through
skin glands
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Temperature
Temperature affects:
• Rate of physiological processes
• Water availability
Adaptations to cold: ?
Adaptations to heat: ?
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Other Climatic Factors
Light affects:
• Plant distribution
• Plant growth rate
• Timing of budding, flowering, fruiting,
leaf shedding
• Animal behavior
• Daily cycles
• Preparation for winter
• Mating and reproduction
Wind affects
vegetation
structure
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Edaphic Factors
Edaphic factors are connected to soil
Soils affect plant growth; plants affect soil characteristics
• Sandy soils hold less water
• High organic matter in soils supports more plant species
• Prairie grassland can build fertile soil
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Disturbance
Disturbance includes: fire, flood
volcanic eruption, storm waves, high
winds
Fire benefits: ?
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Interactions Among Species
•
•
•
•
•
•
Competition: ?
Predation: ?
Parasitism:?
Herbivory: ?
Allelopathy: ?
Symbiosis:?
• Commensalism: one species benefits, the other is unaffected
• Mutualism: one or both species cannot survive alone
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Biogeography
Interactions Among Species
Importance of predation: Rise and fall of the Kaibab deer herd
Predators removed deer population expanded deer overgrazed the
vegetation and starved deer population crashed
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Succession
Ecological Succession: sequence of distinctive plant and animal communities
occurring within a given area of newly formed land or land cleared of plant
cover by burning, clear cutting, or other agents
Primary succession: succession on a new deposit of rock or mineral fragments
Secondary succession: succession on a previously vegetated area that has been
disturbed
Primary
succession
on coastal
dunes
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Succession
Secondary succession on old fields, southeastern U.S.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Ecological Succession
Disturbances may interrupt succession, alter ecosystems and change
successional pathways
• Wind
• Fire
• Floods
• Introduction of new species
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Historical Biogeography
Evolution
Evolution: the creation of diversity of life-forms
through the process of natural selection
Natural selection: selection of organisms by the
environment in a process similar to selection of
plants or animals for breeding by agriculturalists
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Historical Biogeography
Species: ?
Evolution
Natural selection: life posses variation
Individuals with qualities best suited to the
environment are more likely to propagate:
“survival of the fittest”
Sources of variation:
1. Mutation: changes in genetic material
2. Recombination: offspring receives 2
slightly different copies (alleles) of each
gene from parents
Genus: collection of closely
related species that share a
similar genetic evolutionary
history
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Historical Biogeography
Speciation: the process by which species are differentiated
and maintained
Speciation arises from several processes acting over time
• Mutation
• Natural selection
• Genetic drift: chance mutations that don’t have any particular benefit, change
the genetic composition of a population
• Gene flow: opposite to genetic drift--populations exchange genes as individuals
move among populations; keeps gene pool uniform
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Historical Biogeography
Speciation in Galapagos
finches
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Historical Biogeography
Extinction
All species become extinct over geologic
time
Conditions change, and species unable
to adapt become extinct
Human activities may cause
extinctions
Catastrophic natural events may
cause extinctions
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Historical Biogeography
Distribution Patterns
Endemic species: species found in one location or
region, and nowhere else
Cosmopolitan species: distributed very widely
Disjunction: one or more closely related species
found in widely separated regions
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Historical Biogeography
Biogeographic Regions
Closely related species often found near each other
Some species have disjunct distributions
Ratite birds and
tinamous are
related; isolated
when Gondwana
split up
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Biodiversity
Biodiversity: the variety of biological life on Earth or
within a region
Humans have created extinctions by ?
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Biodiversity
Human Impact on the Biosphere
Biodiversity Hotspots
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.