Transcript Chapter 5: Biological Communities: The Biome Concept 1

Chapter 5: Biological
Communities: The Biome Concept
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The Case of the Cactus
Look-Alike
Cactus-like plants are common in Africa.
These plants do not belong to the cactus
family, Cactaceae:
Cactaceae are native only to New World
look-alikes may be in spurge family,
Euphorbiaceae
This situation illustrates convergence of
species descended from different
ancestors.
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Convergence
Convergence is the process by which
unrelated organisms evolve a
resemblance to each other in response
to common environmental conditions:
similar adaptive responses emerge in
response to particular selective conditions
an example: mangroves worldwide
typically have thick, leathery leaves, root
projections, and viviparity
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(a) A tree-forming cactus in Mexico; (b) an East
African euphorb tree. Both converged in
response to dry climate
The Biome Concept
 Character (plant and animal life) of natural communities
is determined by climate, topography, and soil (or
parallel influences in aquatic environments).
 Because of convergence, similar dominant plant forms
occur under similar conditions. Biomes are categories
that group communities by dominant plant forms.
 In North America:
tundra, boreal forest, temperate seasonal forest, temperate rain
forest, shrubland, grassland, and subtropical desert
 In Mexico and Central America:
tropical rain forest, tropical deciduous forest, and tropical
savanna
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Biomes - Key Points
Geographic distributions of biomes
correspond closely to major climate zones.
Not all biome classifications are the same:
some recognize finer or coarser detail
various biomes intergrade continuously and
recognizing boundaries is difficult
Matching of biomes and environment occurs
because no single type of plant can endure
the entire range of conditions on earth.
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Adaptations and Environment -Not the Whole Story
Distributions of species are not solely a
function of relationships to physical
environment:
biotic interactions shape these distributions
chance and history play important roles
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Climate is the major determinant
of plant distribution.
 Climatic factors typically
establish limits of plant
distributions:
the sugar maple, Acer
saccharum, in eastern
North America, is limited
by:
cold winter temperatures
to the north
hot summer temperatures
to the south
summer drought to the
west
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Ecological Tolerances
Several tree-sized maples in eastern North
America have distributions that broadly
overlap that of sugar maple:
because of different ecological tolerances,
these other species exhibit distinctive
environmental preferences, even when their
ranges overlap:
black: drier, better-drained soils high in calcium
silver: moist, well-drained soils
red: wet and swampy or dry, poorly-developed soils
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Related species may differ in
their ecological tolerances
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Topography in mountains creates a
wide range of moisture conditions
 each species exhibits a
local and distinctive
optimum – the type of
site in which it does best
coast redwood dominates
center of moisture
gradient
cedar, Douglas fir,
madrone occur at drier
end of the moisture
gradient
big-leaf maple, California
bay tree occur at wetter
end of moisture gradient
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Form and function match
the environment.
Adaptations match each species to the
environment where it lives:
all species are to some extent specialized:
insect larvae from ditches and sloughs survive
without oxygen longer than related species from wellaerated streams
marine snails from the upper intertidal tolerate
desiccation better than their relatives from lower
levels
we recognize both specialists and generalists
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(b) Paloverde
leaflets are tiny;
thick stems are
responsible for
photosynthesis
(a) Mesquite
leaves are
subdivided into
leaflets that
facilitate
dissipation of
heat
(c) Limberbrush has broad, succulent
leaves produced for only a few weeks
Other Considerations
Certain species make their environments
more favorable for themselves:
decaying foliage of evergreen species of poor
soils produces organic acids, leaching minerals
from soil
Availability of moisture is the single most
important climatic factor defining biomes:
because heat influences moisture stress,
temperature and precipitation together are the
determinants of boundaries of major biomes 14
Climate defines the boundaries of
terrestrial biomes.
A widely adopted climatic classification is
that of Heinrich Walter:
Walter’s scheme is based on the annual
course of temperature and precipitation:
focuses on conditions of moisture and
temperature stress that determine plant form
recognizes 9 zones, from Equatorial (Tropical rain
forest) to Polar (Tundra)
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Walter’s climate zone classification
Whittaker’s Scheme 1
Whittaker related major biomes to annual
temperature and precipitation.
The biomes fall in a triangular area with
corners representing following conditions:
warm-moist
warm-dry
cool-dry
Whittaker’s scheme is similar in many
respects to Walter’s:
Whittaker starts with vegetation and relates
climate
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Whittaker’s Scheme 2
Equatorial and tropical climate zones (mean
temperatures between 20oC and 30oC)
precipitation ranges from 0 to 400+ cm/yr
Temperate climate zones (mean
temperatures between 5oC and 20oC)
precipitation ranges from 0 to 300+ cm/yr
Boreal and polar climate zones (mean
temperatures less than 5oC)
precipitation typically below 200 cm/yr
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Whittaker’s biomes
Whittaker’s Scheme Other Considerations
Fire shapes vegetation toward drier end of
spectrum within each temperature range:
typically in grassland and shrub biomes where:
moisture is intermediate (sufficient productivity for fuels to
accumulate)
seasonal droughts occur (fuels dry out sufficiently to burn)
fire favors grasses and forbs over woody plants
species of these systems are adapted to or are
specialized for frequent fires
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Walter’s Climate Diagrams
Walter’s climate diagrams relate monthly
temperature and precipitation through the year:
20 mm of monthly precipitation is equated with 10oC
in temperature
vertical scales permit ready identification of periods
of water deficit and water abundance
Localities within the same climate zone have
similar climates worldwide.
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Global distribution of major biomes
Temperate Climate Zones
Temperate zone is characterized by
temperatures between 5o-20oC at low
elevations, with frost throughout the zone:
found between 30oN and 45oN in North
America and between 40oN and 60oN in Europe
biomes differentiated by:
total amounts and seasonality of precipitation
length of frost-free season or growing season
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Temperate Seasonal
Forest Biome 1
Develops under moderate climates with
winter freezing:
growing season is 130-180 days
precipitation exceeds evapotranspiration
Found principally in eastern North
America, Europe, and eastern Asia.
Vegetation is dominated by deciduous
trees with understory of small trees and
shrubs, often abundant herbs.
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Temperate Seasonal
Forest Biome 2
Warmer and drier parts of the temperate
seasonal forest biome are dominated by needleleaved trees, typically pines:
found principally in North America along the Atlantic
and Gulf coasts and at higher elevations in the
western states
needle-leaved forests typically develop under
conditions of drought and nutrient stress
fires may be frequent and species can resist fire
damage
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Temperate Rain Forest
Biome
Develops primarily in warm temperate climates:
mild winters, heavy winter rains, summer fogs
common
Found principally in the northwestern US,
adjacent British Columbia, southern Chile, New
Zealand, Tasmania.
Vegetation is dominated by tall evergreen trees,
such as Douglas fir and coastal redwood:
extensive during Mesozoic era
not as diverse as its tropical counterparts
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Temperate
Grassland/Desert Biome 1
Found in continental climate zones:
summers are hot and wet; winters are cold
growing season is 120-300 days
fires are a dominant influence
Extensive grasslands develop, called prairies in
North America, steppes in central Asia.
Vegetation is dominated by grasses and forbs:
fire is frequent and most species have underground
fire-resistant stems
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Temperate
Grassland/Desert Biome 2
 Grasslands grade into deserts in arid continental
climates:
winters are cold and summers hot
precipitation is 25-50 cm/yr
fires are infrequent because of low fuel accumulation
grazing can exert strong pressure on vegetation
 Grasslands are widespread in the western US, from
Great Basin southward.
 Vegetation is dominated by shrubs, such as
sagebrush, or small trees, such as piñon pine and
juniper.
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Woodland/Shrubland Biome
Develops in Mediterranean-type climate (cool,
wet winter, warm dry summer):
fires are frequent and most plants have adaptations
to fire (resistant seeds or root crowns)
Typically found at 30-40o latitude, west coasts,
common in southern Europe, southern
California, central Chile, Cape region of South
Africa.
Vegetation is dominated by sclerophyllous
evergreen shrubs.
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Subtropical Desert Biome
These are highly variable systems found
under extreme aridity:
develop at 20o-30o north and south latitude
rainfall is sparse (less than 25 mm)
creosote bush is common in subtropical
American deserts, with associated cacti,
shrubs, and small trees:
subtropical deserts typically have summer rainfall,
with high species diversity, prominent annual flora
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Boreal and Polar Climate
Zones
These zones have average temperatures
below 5oC.
Boreal forest (taiga) develops between
temperatures of 5oC and -5oC.
Tundra develops at temperatures below 5oC.
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Boreal Forest Biome
Climate is extremely cold, with temperatures as
low as -60oC in winter:
average annual temperature is below 5oC, precipitation
40-100 cm/yr
growing season is 50-100 days
Boreal forest is centered on a broad belt at 5060oN latitude across North America and Eurasia.
Also called taiga, vegetation of low diversity
dominated by evergreen needle-leaved trees,
typically spruce and fir.
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Tundra Biome
 Exceedingly cold climate, with brief, but active, growing
season in summer:
soils are permanently frozen, thaw to depth of 0.5-1 m during
brief summer growing season
precipitation is less than 60 cm/yr, but soils may be saturated
because of impeded drainage
 Found at high latitudes, north of boreal forest belt (but
superficially similar systems occur in alpine zones).
 Tundra is a treeless expanse of dwarf, prostrate woody
shrubs.
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Equatorial and Tropical
Climate Zones
Located within 20o of the equator.
Daily temperature variation exceeds
monthly variation through the year.
Environments are largely distinguished by
differences in the seasonal pattern of
rainfall.
Frost is not a factor; plants and animals
cannot tolerate freezing.
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Tropical Rain Forest Biome
 Climate is continually warm and moist:
precipitation is in excess of 200 cm/yr, biseasonal, but never
less than 10 cm in any month
 Occupies three important regions, in South/Central
America, West Africa, Indo-Malayan region.
 These are exceedingly diverse forests, dominated by
evergreen or seasonally deciduous broad-leaved trees,
featuring diverse growth forms including climbing lianas
(woody vines) and epiphytes (plants that grow on the
branches of other plants).
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Tropical Seasonal
Forest/Savanna Biomes 1
climate is seasonally dry, but sufficient
moisture to support forest:
progressively drier tropical habitats support
dry forests, thorn scrub, and true deserts
Occur worldwide within the tropics, but
typically beyond 10oN or S of the equator.
Tropical seasonal forests have a
preponderance of deciduous species.
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Tropical Seasonal
Forest/Savanna Biomes 2
Savannas are grasslands with scattered trees.
These are typical of large areas of semiarid
tropics, especially at high elevations in East
Africa.
Rainfall is strongly seasonal:
90-150 cm/yr but driest 3-4 months receive less than
5 cm each
fire and grazing play important roles in maintenance
of these system
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A pause…
Rainforests today
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Rain forests today
 More than one half of tropical forests have already been destroyed
 Rainforests once covered 14% of the earth's land surface; now they
cover a mere 6% and experts estimate that the last remaining
rainforests could be consumed in less than 40 years.
 each day at least 80,000 acres (32,300 ha) of forest disappear from
Earth. At least another 80,000 acres (32,300 ha) of forest are
degraded. Hundreds of species driven to extinction
 FAO estimates that 10.4 million hectares of tropical forest were
permanently destroyed each year in the period from 2000 to 2005, an
increase since the 1990-2000 period, when around 10.16 million
hectares of forest were lost
 Experts estimates that we are losing 137 plant, animal and insect
species every single day due to rainforest deforestation. That equates
to 50,000 species a year. As the rainforest species disappear, so do
many possible cures for life-threatening diseases. Currently, 121
prescription drugs sold worldwide come from plant-derived sources.
While 25% of Western pharmaceuticals are derived from rainforest
ingredients, less that 1% of these tropical trees and plants have been
tested by scientists.
 There were an estimated ten million Indians living in the Amazonian
5/23/2016
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Rainforest five centuries ago. Today there are less than 200,000.
5/23/2016
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Deforestation for cattle grazing
5/23/2016
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Modification of the Biome
Concept for Aquatic Ecosystems
The biome concept in its strict sense does
not exist for aquatic ecosystems:
biomes were developed for terrestrial
ecosystems, where growth form of dominant
vegetation is distinguishing factor
aquatic ecologists have tended to develop
independent classifications for aquatic
systems, focused predominantly on physical
factors
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Aquatic Ecosystems Streams
Streams form wherever precipitation exceeds
evaporation, draining excess water.
Streams may be divided into principal habitats:
riffles (where water runs over rocky substrate)
pools (deeper stretches of slow-moving water)
Streams exhibit continuous change in
conditions from headwaters downstream,
captured in river continuum concept.
Streams exhibit downstream drift of
organisms/material.
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Conditions
of a stream
differ in
pools and
riffles
Aquatic Ecosystems Lakes
Lakes form in any kind of depression
(typically effects of glaciation or geological
activity).
May be divided into principal habitats:
littoral zone (shallow zone with rooted
vegetation)
limnetic zone (open water beyond littoral
zone)
benthic zone (bottom sediments, habitat for
burrowing animals and microorganisms)
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Ecological
zones in a
lake
Aquatic Ecosystems Estuaries
Are special environments at the mouths of
rivers, especially where outflow is partially
enclosed (such as barrier islands).
Unique because they are the interface between
fresh and salt water habitats:
typically highly productive because of influx of
nutrients and their rapid exchange between
sediments and surface waters
often edged by extensive tidal marshes with
emergent vegetation
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Estuaries …
Aquatic Ecosystems Oceans
Oceans are enormously complex systems, with
conditions varying with temperature, depth,
current, substrate, tides.
Oceans are often classified according to depth:
littoral zone (between high and low tides, exhibits
dramatic zonation)
neritic zone (beyond low tide to edge of continental
shelf, often subdivided into photic and aphotic
zones, typically productive)
oceanic zone (deeper waters, also divided into
photic and aphotic zones, typically unproductive)
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Ocean’s ecological
zones
Aquatic Ecosystems Coral Reefs
Coral reefs are special oceanic systems:
develop in shallow waters of warm oceans
may develop around volcanoes, which may
subside or erode, leaving a ring-like atoll
are typically highly productive:
nutrients released from erosion on landward
side
nutrients forced up as deeper-water currents
encounter the reef
are typically highly diverse
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Coral
reefs in
the Red
Sea
Summary 1
Climate has profound effects on dominant plant
forms. Each region has characteristic
vegetation differing in growth form, leaf
morphology, and seasonality of foliage.
Major vegetation types can be used to classify
ecosystems into biomes associated with major
climatic classes.
Walter’s approach classifies regions on the basis
of climates having characteristic vegetation.
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Summary 2
Whittaker’s approach classifies regions on the
basis of vegetation having characteristic
climates.
Principal climatic zones (tropical, temperate,
boreal, polar) and their biomes are distinguished
first on the basis of temperature, then
precipitation, and its seasonality.
Aquatic systems are not classified into biomes,
but we distinguish streams, lakes, estuaries,
oceans, and coral reefs.
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As usual…
Do quiz for chapter 5 – due Monday
Reminder: quiz – chapters 1 to 4, March
17 (for BIOL 207) and March 18 (for
PDHP 212)
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