The Case of the Cactus Look-Alike
Lecture 5:
Biological Communities:
The Biome Concept
Pages 98-124
Convergence
• Convergence is the process by which unrelated
organisms evolve a resemblance to each other in
response to common environmental conditions:
– e.g., the leafless, thick, fleshy branches of cactus and
the cactus-like euphorb evolved adaptations to reduce
water loss in semi-arid environments
– e.g., mangroves worldwide typically have thick, leathery
leaves, root projections, and viviparity
• 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
________________________
of species descended from
different ancestors.
The Biome Concept
• Changing character of plant and animal life is
determined by climate, topography, and soil
(or parallel influences in aquatic
environments).
• Because of convergence, similar dominant
plant forms occur under similar conditions.
• _________________ are categories that
group communities by dominant plant forms.
Biomes - Terrestrial Examples
• 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
Biomes - Key Points
• Geographic distributions of biomes
correspond closely to major climate zones.
• Not all biome classifications are the same:
– some recognize ____________________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:
– ______________interactions shape these
distributions
– ________________________play
important roles
Ecological Tolerances
Climate is the major determinant
of plant distribution.
• Climatic factors
typically establish limits
of plant distributions:
– 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
Variations in topography and soils influence plant
distributions.
other species exhibit distinctive environmental
preferences, even when their ranges overlap:
• Topography in mountains creates a wide range of
soil conditions
• Characteristics of soil that influence the distribution
of plants are called __________________factors.
• each species exhibits a local and distinctive
___________________________– the type of site
in which it does best.
• in northern California:
• black: drier, better-drained soils high in calcium
• silver: moist, well-drained soils
• red: wet and swampy or dry, poorly-developed soils
• 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
• Several tree-sized maples in eastern North
America have distributions that broadly
overlap that of sugar maple:
- because of different__________________, these
Form and function match the
environment.
• Adaptations match each species to the
environment where it lives:
– all species are to some extent specialized:
• marine snails from the upper intertidal tolerate
desiccation better than their relatives from lower
levels
– we recognize both __________________
and _________________________
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 ____________________ 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
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Climate defines the boundaries
of terrestrial biomes.
• A widely adopted climatic classification is
that of Heinrich Walter: climate zone system
– Walter’s scheme is based on the annual course
of _______________and _________________:
• focuses on conditions of moisture and temperature
stress that determine plant form
• recognizes 9 zones, from Equatorial (Tropical rain
forest) to Polar (Tundra)
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.
Whittaker’s Scheme 1
• Whittaker related _________________________
of 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
Whittaker’s Scheme 2
• Equatorial and tropical climate zones
(mean temperatures between 20oC and
30oC)
– precipitation ranges from 0 to 400+ cm/yr
• _______________ climate zones (mean
temperatures between 5oC and 20oC)
– precipitation ranges from 0 to 300+ cm/yr
• __________ and polar climate zones
(mean temperatures less than 5oC)
– precipitation typically below 200 cm/yr
Whittaker's biomes are delineated according to
average temperature and precipitation
Whittaker’s Scheme - Other
Considerations
• __________________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 _____________and ____________
over woody plants
– species of these systems are adapted to or are
specialized for frequent fires
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Temperate Climate Zones
• Temperate zone is characterized by
temperatures between ____________
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
Temperate Rain Forest Biome
• Develops primarily in ______
_____________ climates:
– mild winters, heavy winter rains,
summer fogs common
Temperate Seasonal Forest Biome
• Develops under moderate
climates with winter
freezing:
– _________________ 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.
Temperate Grassland/Desert Biome 1
• Found in ___________
climate zones:
– summers are hot and wet;
winters are cold
– growing season is 120-300 days
– fires are a dominant influence
• 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 grasslands develop,
called ____________ in North
America, ____________ in
central Asia.
• Vegetation is dominated by
grasses and forbs:
– extensive during Mesozoic era
– not as diverse as its tropical
counterparts
– fire is frequent and most species
have underground fire-resistant
stems
Temperate Grassland/Desert Biome 2
• Grasslands grade into
_____________ 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_________________, such
as sagebrush, or small trees,
such as piñon pine and
juniper.
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
____________________________
evergreen shrubs.
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Subtropical Desert Biome
• These are highly __________________
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
Boreal Forest Biome
• Climate is extremely cold, with temperatures as
low as -60oC in winter:
– average annual temperature is below __________
– precipitation 40-100 cm/yr
– growing season is____________________ 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.
Equatorial and Tropical
Climate Zones
• Located within ________of the equator.
• Daily temperature variation exceeds
monthly variation through the year.
• Environments are largely distinguished
by differences in the seasonal pattern of
rainfall.
• _____________ is not a factor; plants
and animals cannot tolerate freezing.
Boreal and Polar Climate Zones
• These zones have average
temperatures below 5oC.
• Boreal forest (_____________)
develops between temperatures of 5oC
and -5oC.
• _______________________develops
at temperatures below -5oC.
Tundra Biome
• Exceedingly cold climate, with brief, but active,
growing season in summer:
– soils are permanently _________________________, 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______________________, north of boreal
forest belt (but superficially similar systems occur in
alpine zones).
• Tundra is a treeless expanse of dwarf, prostrate
woody shrubs.
Tropical Rain Forest Biome
• Climate is continually warm and moist:
– precipitation is in excess of_______________,
biseasonal, but never less than 10 cm in any
month
• Occupies three important regions, in
South/Central America, West Africa, IndoMalayan region.
• These are exceedingly diverse forests,
dominated by evergreen or seasonally
deciduous broad-leaved trees, featuring
diverse growth forms including lianas and
_________________________
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Tropical Seasonal
Forest/Savanna Biomes 1
Tropical Seasonal
Forest/Savanna Biomes 2
• Found where climate is_______________,
but has sufficient moisture to support forest:
• Savannas are ______________________
with scattered trees.
• These are typical of large areas of semiarid
tropics, especially at high elevations in East
Africa.
• Rainfall is strongly ____________________:
– 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 __________________
species.
Modification of the Biome Concept
for Aquatic Ecosystems
• The biome concept in its strict sense
does not exist for
______________________________:
– 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
Aquatic Ecosystems - Lakes
• Lakes form in any kind of depression
(typically effects of glaciation or geological
activity).
• May be divided into principal habitats:
– _________________ zone (shallow zone
with rooted vegetation)
– limnetic zone (open water beyond littoral
zone)
– __________zone (bottom sediments, habitat
for burrowing animals and microorganisms)
– 90-150 cm/yr but driest 3-4 months receive less
than 5 cm each
– fire and _______________ play important roles in
maintenance of these system
Aquatic Ecosystems - Streams
• Streams form wherever precipitation exceeds
evaporation, draining excess water.
• Streams may be divided into principal habitats:
– ________(where water runs over rocky substrate)
– runs (deeper stretches of slow-moving water)
• Streams exhibit continuous change in
conditions from headwaters downstream,
captured in _____________________concept.
• Streams exhibit downstream drift of
organisms/material.
Aquatic Ecosystems - Estuaries
• Are special environments at the __________
of rivers, especially where outflow is partially
enclosed (such as barrier islands).
• Unique because they are the ___________
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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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)
– _____________ zone (beyond low tide to edge of
continental shelf, often subdivided into photic and
aphotic zones, typically productive)
– _____________ zone (deeper waters, also divided into
photic and aphotic zones, typically unproductive)
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.
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
__________
– are typically highly productive:
• nutrients released from erosion on landward side
• nutrients forced up as deeper-water currents
encounter the reef
– are typically highly__________________
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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