Transcript Table of Contents - Milan Area Schools

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Introduction
• Biogeography is the study of the patterns of
distribution of populations, species, and
communities across Earth.
• The question of why a species occurs in a
particular location has two possible answers:
 It evolved there or it moved there from
elsewhere.
 If a species is absent, either it was never there
or it was once present but no longer lives
there.
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Earth’s Biogeographic Regions
• Earth can be divided into seven major
biogeographic regions.
• A species found only in a certain region is
endemic to that region.
• Remote islands such as Madagascar typically
have distinctive endemic biotas because water
barriers greatly restrict migration.
• Most species are confined to a single
biogeographic region, but Homo sapiens is the
most widespread species on Earth today.
Figure 56.1 Major Biogeographic Regions
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History and Biogeography
• Past events influence the distribution of species
on Earth.
• Early biogeographers, such as Linnaeus, believed
that the continents were fixed in their positions,
and that all organisms were created in one place
from which they later dispersed.
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History and Biogeography
• In 1912, Alfred Wegener proposed the idea of
continental drift, based on several observations:
 The shapes of the continents (e.g., Africa and
South America) seem to fit together like a
puzzle.
 The alignment of mountain chains, rock strata,
and glacial deposits suggest movement over
time.
 The distribution of organisms on Earth is hard
to explain if one assumes the continents never
moved.
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History and Biogeography
• Area phylogenies: Describe when and where
evolutionary lineages originated.
• To generate an area phylogeny, the names in a
taxonomic phylogeny are replaced with the names
of the places where those taxa live or lived.
• An area phylogeny suggests that horses
speciated as they moved from Africa to Asia.
• To infer the approximate times of separation of
lineages, biogeographers use molecular
difference between species, fossils to determine
how long a taxon has been in an area, and the
distribution of living species.
Figure 56.3 Taxonomic Phylogeny to Area Phylogeny (Part 1)
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History and Biogeography
• A vicariant event is the appearance of a barrier
that splits the range of a species.
• Vicariant events include sea level changes,
mountain building, and continental movement.
• If members of a species cross an existing barrier
and establish a new population, the species’
disrupted range is the result of dispersal.
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History and Biogeography
• By studying a single evolutionary lineage as well
as distribution patterns among lineages, scientists
can:
 Discover the roles of vicariant events.
 Investigate the role dispersal played in
determining today’s distribution patterns.
• The longer an area has been isolated from other
areas, the more endemic taxa it is likely to have.
 Austrailia vs North America/Euasia.
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History and Biogeography
• When several hypotheses can explain a pattern, the
parsimonious hypothesis (that which requires the
least number of unobserved events to explain it) is
generally preferred.
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Ecology and Biogeography
• The climate of a region is the average of the
atmospheric conditions found there over time.
• Climates vary greatly on Earth and influence the
geographic distribution of species.
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Ecology and Biogeography
• Solar energy inputs drive global climates.
• Every place on Earth receives the same total
number of hours of sunlight each year, but not the
same amount of energy.
• The rate at which solar energy arrives at the
Earth’s surface depends primarily on the angle of
the sunlight.
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Ecology and Biogeography
• Earth’s climates are strongly influenced by global
air circulation patterns which result from global
variation in solar input.
• Air rises when heated and releases moisture.
Warm air rises in the Tropics and is replaced by
air flowing towards the equator from north and
south. The intertropical convergence zone is
where these air masses come together.
• Heavy rains usually fall in a region when it is close
to the intertropical convergence zone.
Figure 56.6 The Circulation of Earth’s Atmosphere
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Ecology and Biogeography
• When air encounters mountain ranges, it rises,
cools, and drops moisture on the windward slopes
resulting in a precipitation distribution called a
rain shadow where the leeward slopes are dry.
Figure 56.7 A Rain Shadow
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Terrestrial Biomes
• Ecologists classify communities of organisms into
biomes.
• Biomes are major ecosystem types based on the
structure of the dominant vegetation.
• The vegetation of a biome has a similar
appearance wherever that biome is found on
Earth.
• The distribution of biomes on Earth is influenced
by annual patterns of temperature and rainfall.
• Each biome has a characteristic climate,
seasonality, and vegetation, and typical patterns
of species richness.
Figure 56.9 Biomes Have Distinct Geographic Distributions
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Terrestrial Biomes
• The tundra biome is found in the Arctic and high
on mountains.
• In the Arctic, permanently frozen soil
(permafrost) underlies tundra vegetation.
• Plants grow only during the short summers when
the first few centimeters of permafrost melt.
• Lowland Arctic tundra is very wet because water
cannot drain through the permafrost.
• Arctic tundra animals either migrate into the area
for the summer only or are dormant for most of
the year.
Biomes: Tundra (Part 2)
Biomes: Tundra (Part 3)
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Terrestrial Biomes
• The boreal forest biome is found south of the
tundra biome and at lower elevations on temperatezone mountains.
• Winters are long and very cold, while summers are
short and warm.
• The short summer favors trees with evergreen
leaves.
• Boreal forests have only a few tree species.
• Northern Hemisphere forests are dominated by
coniferous evergreen gymnosperms.
• Southern Hemisphere forests are dominated by
beech trees.
Biomes: Boreal Forest (Part 2)
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Terrestrial Biomes
• The temperate deciduous forest biome is found
in eastern North America, eastern Asia, and
western Europe. MICHIGAN!!!
• Temperatures fluctuate dramatically from season
to season.
• Precipitation is evenly distributed throughout the
year.
• Deciduous trees lose their leaves during the
winter.
• Many more tree species are present relative to
boreal forests.
Biomes: Temperate Deciduous Forest (Part 2)
Biomes: Temperate Deciduous Forest (Part 3)
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Terrestrial Biomes
• The temperate grassland biome is found in
many parts of the world, all of which are relatively
dry much of the year.
• Most grasslands have hot summers and cold
winters.
• Grasslands are structurally simple, but they are
rich in species.
• Most of the grassland biome has been converted
to agriculture.
Biomes: Temperate Grasslands (Part 2)
Biomes: Temperate Grasslands (Part 3)
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Terrestrial Biomes
• The hot desert biome is found in two belts,
centered around 30north and 30south
latitudes.
• Central Australia and the middle of the Sahara
Desert are the driest regions within the biome.
• Succulent plants that store large quantities of
water in their stems are common. Annual plants
germinate and grow when rain falls.
Biomes: Hot Desert (Part 1)
Biomes: Hot Desert (Part 2)
Biomes: Hot Desert (Part 3)
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Terrestrial Biomes
• The chaparral biome is found on the west sides
of continents at moderate latitudes, where cool
ocean waters flow offshore.
• The Mediterranean region of Europe, coastal
California, and central Chile are examples of
chaparral.
• Low-growing shrubs and trees with evergreen
leaves are the most common plants in chaparral.
• Large populations of small seed-eating rodents
are present in the biome.
Biomes: Chaparral (Part 2)
Biomes: Chaparral (Part 4)
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Terrestrial Biomes
• Thorn forests are found on the equatorial sides
of hot deserts. The climate is semi-arid with little
or no rain in winter, but sometimes heavy rain in
summer.
• The dominant plants are spiny shrubs and small
trees. Acacia is common.
• Savannas are found in dry tropical and
subtropical regions of Africa, South America, and
Australia.
• The savanna biome is characterized by its vast
expanses of grassland and scattered trees, and
by huge numbers of grazing and browsing
mammals.
Biomes: Thorn Forest and Tropical Savanna (Part 4)
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Terrestrial Biomes
• The tropical deciduous forest biome is found
closer to the equator relative to thorn forests and
has a long summer rainy season.
• Species richness is moderate for plants and high
across all other categories, including mammals,
birds, reptiles, and amphibians.
Biomes: Tropical Deciduous Forest (Part 2)
Biomes: Tropical Deciduous Forest (Part 3)
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Terrestrial Biomes
• Tropical evergreen forests are found in
equatorial regions where total rainfall exceeds
250 cm annually.
• The biome is the richest on Earth in both plant
and animal species.
• Overall productivity of tropical evergreen forests is
the highest among terrestrial ecological
communities.
Biomes: Tropical Evergreen Forest (Part 2)
Biomes: Tropical Evergreen Forest (Part 3)
Biomes: Tropical Evergreen Forest (Part 4)
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Aquatic Biogeography
• About 2.5 percent of Earth’s water is found in
ponds, lakes, and streams.
• Freshwater ecosystems contain about 10 percent
of all aquatic species.
• More than 25,000 insect species such as
dragonflies have at least one aquatic stage in
their lives (usually the larva).
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Aquatic Biogeography
• Ocean water moves in great circular patterns
which determine biogeographic patterns.
• Most marine organisms have restricted ranges.
• Water temperature and salinity can be barriers to
dispersal of marine organisms.
• Deep ocean waters prevent the dispersal of
marine organisms that live only in shallow water.
• Richness of shallow-water species near isolated
islands of the Pacific decreases with distance
from the larger islands of Indonesia.
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Regional Patterns of Species Richness
• Species richness on islands is always less than
an equivalent area of the mainland.
• Species richness on islands is positively
correlated with island size and inversely
correlated with distance from the mainland.
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Regional Patterns of Species Richness
• Over periods of a few hundred years, species
richness is influenced by immigration of new
species and the extinction of existing species.
• The MacArthur-Wilson model.
• The rate of immigration and extinction on an
island is affected by the size of the island and
distance from the mainland.
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Regional Patterns of Species Richness
• Major disturbances can sometimes serve as
“natural experiments.”
• The eruption of Krakatau in 1883 destroyed all life
on the island’s surface, but it provided a test of the
MacArthur and Wilson model.
• By 1933 the island was again covered by a
tropical evergreen forest.
• While forest canopy was recovering, there were
high rates of colonization. Today, rates of
colonization are not as fast, but colonization and
extinctions are still occurring.