Transcript Spatial groupings, part 2

GEO 200: Physical Geography
Terrestrial Biota (1 of 2)
Geographical questions
• What is the range of a species or group of species?
• What are species or groups of species distributed as
they are?
• What is the significance of the distribution pattern?
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Natural distributions
• Four conditions determine the natural distribution of
any species or group of organisms:
–
–
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Evolutionary development
Migration/dispersal
Reproductive success
Extinction
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Evolutionary development
• According to the Darwinian theory of natural
selection, the origin of any species is a normal
process of descent, with modification, from parent
forms.
• Origin of species or genus can have either:
– A very localized beginning
– Similar evolutionary development at several scattered
localities.
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Migration and dispersal
• Movement of organisms can have
– Active mechanisms
– Passive mechanisms
• Passive mechanism particularly influential in seed stage, through
wind, water, and animals.
• The contemporary distribution pattern of many
organisms is often the result of natural migration or
dispersal from an original center(s) of development.
– Examples are the cattle egret and coconut palm.
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Reproductive success
• There are a number of reasons can cause poor
reproductive success, among them:
– Heavy predation
– Climatic change
– Failure of food supply.
• Reproductive success is usually the limiting factor
that allows one competing population to flourish
while another languishes.
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Extinction
• No species is likely to be a permanent inhabitant of
Earth.
• Plant succession is the process whereby one type of
vegetation is replaced naturally by another.
– Succession is a spatially and temporally variable process; it
is not a permanent loss like extinction.
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Terrestrial flora
• Geographers are interested in natural vegetation of
landscape for three reasons:
– Plants are likely to dominate a landscape (except where
terrain is rugged, climate is harsh, or humans have
intervened);
– Vegetation is a sensitive indicator of other environmental
attributes;
– Vegetation is often instrumental to human settlement and
activities.
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Characteristics of plants, part 1
• Most are very hardy
– Plants’ high survival potential is dependent on
• Subsurface root system
• Reproductive mechanism
• Perennials are plants that can live more than a single year despite
seasonal climatic variations.
• Annuals are plants that perish during times of climatic stress but
leaves behind a reservoir of seeds to germinate during the next
favorable period.
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Characteristics of plants, part 2
• Most are very hardy (continued)
– Common characteristics:
• Roots (to gather nutrients and moisture and to anchor plant);
• Stems and branches (to support and transport nutrients);
• Leaves (to collect solar energy, exchange gases, and transpire
water);
• Reproductive organs.
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Adaptations of plants, part 1
• Environmental adaptations
– Two prominent adaptation strategies of plants to protect
against environmental stress are
• Xerophytic adaptations
– Xerophytic refers to plants structurally adapting to withstand
protracted dry conditions.
– Roots, stems, leaves, reproductive cycle can all adapt in various ways.
– Succulents are plants that have fleshy stems that store water.
• Hygrophytic adaptations
– Hygrophytic refers to plants structurally adapting to withstand
protracted wet conditions.
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Adaptations of plants, part 2
• Hygrophytic adapatation
– A hygrophyte is a plant that requires a saturated or semisaturated environment (frequent soakings with water).
• Hygrophytes are likely to have extensive root systems for
anchoring in soft ground.
• They usually rely on buoyancy of water for support rather than
stem.
– Many have weak, pliable stems that can withstand currents.
• Hydrophytes are often grouped in with this category.
– A hydrophyte is a “water-loving” plant that is adapted to live in more
or less permanently immersed in water.
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Role of competition
• Competition is key in which plants grow where.
– Even though all conditions (climatic, edaphic, etc.) are
favorable, a plant may not take hold in one area because of
competition.
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Floristic terminology, part 1
• Categorizing by reproduction
– Through spores
• Those that reproduce by spores are in two major groups:
• Bryophytes are spore-bearing plants such as mosses and liverworts;
never dominated in history, but can be very important in some
localized situations.
• Pteridophytes are spore-bearing plants such as ferns, horsetails, and
clubmosses; used to dominate continental vegetation, but no more.
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Floristic terminology, part 2
• Categorizing by reproduction (continued)
– Through seeds
• Those that reproduce by seeds are in two major groups:
• Gymnosperms are seed-reproducing plants that carry their seeds in
cones; also known as conifers.
• Gymnosperms were the dominant plant group in the past.
• Angiosperms are plants that have seeds encased in some sort of
protective body, such as a fruit, a nut, or a seedpod.
• Angiosperms have dominated planet vegetation for last 50 million
to 60 million years.
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Floristic terminology, part 3
• Categorizing by stem or trunk composition
– Woody plants have a stem composed of hard fibrous
material; refers mostly to trees and shrubs.
– Herbaceous plants have soft stems; they are mostly grasses,
forbs, and lichens.
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Floristic terminology, part 4
• Categorizing by leaf retention
– Deciduous trees and shrubs experience an annual period in
which all leaves die and usually fall from the tree, due
either to a cold or dry season.
– Evergreen trees or shrubs sheds their leaves on a sporadic
or successive basis, but at any given time they appear to be
fully leaved.
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Floristic terminology, part 5
• Categorizing by leaf shape
– Broadleaf trees have flat and expansive leaves.
• Majority are deciduous.
• In rainy tropics, everything is evergreen.
– Needleleaf trees are adorned with thin slivers of tough,
leathery, waxy needles rather than typical leaves.
• Almost all are evergreen.
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Floristic terminology, part 6
• Categorizing by supposed structure (this works for
foresters, but not geographers)
– Hardwoods are angiosperm trees that are usually broadleaved and deciduous.
• The wood has a relatively complicated structure, but is not always
hard.
– Softwood are gymnosperm trees.
• Nearly all such trees are needle-leaved evergreens with wood of
simple cellular structure but not always soft.
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Spatial groupings, part 1
• Geographers are usually more concerned with spatial
groupings than individual plants.
– Groups are based on dominant members, dominant
appearance, or both.
• The floristic pattern of Earth is impermanent.
– Change can be slow and orderly, as in lake infilling.
– Change can be abrupt and chaotic, as in wildfire.
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Spatial groupings, part 2
• Floristic pattern of Earth (continued)
– Climax vegetation is a stable plant association of relatively
constant composition that develops at the end of a long
succession of changes.
• Is an association in equilibrium with prevailing environmental
conditions.
• Should persist until environmental disturbance/change occurs.
– Seral associations are various stages leading up to climax
vegetation.
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Spatial groupings, part 3
• Geographers can face significant difficulties in
recognizing spatial groupings.
– As one tries to identify patterns and recognize
relationships, must make generalizations.
• When associations are portrayed on maps, boundaries usually
represent approximations.
– Human interference plays a major role.
• Because of human impact, climax vegetation is now the exception
rather than rule.
• Maps often ignore human interference, so are actually maps of
theoretical natural vegetation.
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Spatial groupings, part 4
• Spatial groupings of plants (continued)
– There are many ways to classify plant associations.
• Geographers usually place emphasis on structure and appearance of
dominant plants.
• Major associations include forests, woodlands, shrublands,
grasslands, deserts, tundra, and wetlands.
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Spatial groupings, part 5
• Classification of plant associations (continued)
– Major associations (continued)
• A forest is an assemblage of trees growing closely together so that
their individual leaf canopies generally overlap.
– Forests are likely to become the climax association in any area where
moisture is adequate and the growing season is not very short.
• A woodland is a tree-dominated association in which the trees are
spaced more widely apart than those of forests and do not have
interlacing canopies.
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Spatial groupings, part 6
• Classification of plant associations (continued)
– Major associations (continued)
• A shrubland is a plant association dominated by relatively short
woody plants.
– Shrublands have a wide latitudinal range but usually are restricted to
semiarid or arid areas.
• A grassland is a plant association dominated by grasses and forbs.
– Prominent grassland types include savanna, prairie, and steppe.
– Grasslands are associated with semiarid and subhumid climates.
• A desert is actually a climate type, not an association per se, but is
typified by plants widely scattered on bare ground.
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Spatial groupings, part 7
• Classification of plant associations (continued)
– Major associations (continued)
• Tundra is a complex mix of very low-growing plants, including
grasses, forbs, dwarf shrubs, mosses, and lichens, but no trees.
– Tundra only occurs in the perennially cold climates of high latitudes
or high altitudes.
• A wetland is a landscape characterized by shallow, standing water
all or most of the year, with vegetation rising above the water level.
– Wetlands have a much more limited geographic extent than any other
above associations.
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Spatial groupings, part 8
• Various plant associations will exist in relatively
narrow zones when mountain slopes have significant
elevational changes in short horizontal distances.
– Vertical zonation is the horizontal layering of different
plant associations on a mountainside or hillside.
• Elevation changes mirror latitude changes.
• Treeline elevation vary with latitude.
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Spatial groupings, part 8
• Elevational changes (continued)
– Vertical zonation (continued)
• Southern and Northern hemispheres experience different elevationlatitude relationship, with the Southern Hemisphere having lower
treelines.
• The reason for the discrepancy is not understood yet.
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Spatial groupings, part 10
• Can have significant local variations caused by a
variety of local environmental conditions.
– Exposure to sunlight is often a critical determinant of
vegetation composition.
• An adret slope is a Sun slope; a slope where the Sun’s rays arrive at
a relatively direct angle.
• An adret slope is relatively hot and dry, and its vegetation is sparser
and smaller than that on adjacent slopes with different exposures.
• Adret slopes are likely to have a species composition different from
adjacent slopes.
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Spatial groupings, part 11
• Local variations (continued)
– Exposure to sunlight (continued)
• A ubac slope is a slope where sunlight strikes at a low angle and
hence is much less effective in heating and evaporating than on the
adret slope, thus producing more luxuriant vegetation of a richer
diversity.
• The differences between adret and ubac decreases with increasing
latitude.
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Spatial groupings, part 12
• Local variations (continued)
– Valley-bottom locations can have vegetation composition
significantly different from slopes running to it.
• Riparian vegetation is streamside growth, particularly prominent in
relatively dry regions, where stream courses may be lined with
trees, although no other trees are to be found in the landscape.
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Terrestrial fauna
• Animals occur in much greater variety than plants
over Earth.
– Animals, however, tend to be much less prominent than
plants in the landscape.
• They tend to be secretive and inconspicuous.
– Also, environmental relationships are much less clearly
evidenced by animals than plants.
• Their inconspicuousness makes it more difficult to study them, and
their mobility had lead to greater environmental adaptability among
them.
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Characteristics of animals
• The variety of animal life is so great that it is difficult
to find many unifying characteristics.
• The two universal traits (though these aren’t always
immediately recognizable) of animals are:
– Mobility
– Need to eat plants and/or other animals
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Environmental adaptations
• Animals have three different kinds of evolutionary
adaptations:
– Physiological adaptations are anatomical or physiological
changes in response to conditions.
– Behavioral adaptations include actions animals can take
(unlike plants) to minimize stresses, such as hunger,
temperature extremes, etc.
– Reproductive adaptations include changes in timing of
reproduction, in rearing of offspring, or in numbers of
offspring produced that increase survival of young.
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Adaptations to desert life, part 1
• Faunal diversity can be astounding in desert areas
where water availability is permanent or prolonged.
• Even in areas where open water is not available, there
are pockets of localized favorable habitat that permit
remnant populations to survive.
• Most desert animals are completely nocturnal.
• Animals are more conspicuous when conditions are
cooler, such as at night and winter.
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Adaptations to desert life, part 2
• Some animals follow the rains in nomadic fashion.
– This behavior is most prominently displayed by birds.
• Some spend significant time underground.
– Some animals bury themselves to survive long dry spells,
such as freshwater crayfish and crabs.
• A few species of rodents can exist from birth to death
without ever taking a drink.
– They get their moisture from food.
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Adaptations to desert life, part 3
• Some species display the ability to delay reproductive
processes over long dry periods until more favorable
conditions occur.
– Australian desert kangaroos can delay implantation of a
fertilized blastocyst (an early embryonic stage), so it
remains in an inactive state in the uterus until better
weather conditions occur.
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The dromedary, part 1
• The dromedary (one-humped) camel has developed
the most remarkable series of adjustments to desert
environment.
• Anatomical adaptations
– Summer coat is light colored and shiny to reflect rather
than absorb sunlight.
– The hair protects against heat absorption from surrounding
environment.
– The split upper lip may allow recapture of moisture lost
through the nostrils.
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The dromedary, part 2
• Anatomical adaptations (continued)
– Nostrils are slit-shaped themselves, which allows them to
be shut to keep out blowing dust and sand.
– Eyes set beneath shaggy, beetle-brows to shade them from
bright sunlight.
– Eyes are further protected by double eyelids against
blowing dust and sand.
– Feet are shaped like broad pads that provide insulation
from the heat of the ground.
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The dromedary, part 3
• Anatomical adaptations (continued)
– Feet are likewise firm and flexible to provide purchase in
the sand.
• Physiological adaptations
– Dromedaries can tolerate much greater fluctuations in body
temperatures that most other large mammals.
• As a result, they sweat relatively little, thus conserving fluids.
– They lose very little water in urine and feces.
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The dromedary, part 4
• Physiological adaptations (continued)
– They have a tremendous ability to maintain bloodstream
moisture during water stress.
• Thus they can experience relatively extreme dehydration before
their body temperature rises to lethal levels.
– Dromedaries can go long periods of time without drinking,
and when they do drink, they become completely
rehydrated quickly.
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Animal competition, part 1
• Competition can be both direct and indirect.
– Indirect competition is a rivalry for space and resources.
– Direct competition is antagonism of predation.
• Many animals create social groups.
– Some create social groups among their own species.
– Some create social groups across species, such as
communal relationship among zebras, wildebeest and
impalas in East African savannas.
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Animal competition, part 2
• Individual animals are concerned either largely or
entirely with own survival.
– Some animal species are concerned with survival of mates.
– Some are concerned with survival of young.
• This is displayed most often as maternal instinct, though some
species exhibit paternal instinct, too.
– Still fewer species are concerned with survival of the
group.
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Animal cooperation
• Symbioses are an association of two dissimilar
organisms, in which they live together in some
fashion.
– Mutualism is a symbiotic relationship in which the
association is mutually beneficial to both organisms.
– Commensalism is a symbiotic relationship in which the
association is neither beneficial nor injurious to either.
– Parasitism is a symbiotic relationship, in which the
association benefits one, but harms the other; that is, one
lives on or in the other, to detriment of the host.
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Kinds of animals, part 1
• Size and habits are not valid indicators of an animal’s
significance to geographic study.
– Minute and seemingly inconsequential organisms can play
important roles.
• Examples include carriers of disease and providers of scarce
nutrients.
• More than 90% of all animal species are invertebrates
(without backbones).
– Arthropods are the most prominent (insects, spiders,
centipedes, millipedes, crustaceans).
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Kinds of animals, part 2
• There are five groups of vertebrates, those with
backbones: fish, amphibians, reptiles, birds, and
mammals.
– Most mammals are placentals, having young grow and
develop in their mother’s body.
– About 135 species are marsupials, in which mothers carry
young, which are not fully developed at birth, in pouches.
– Two species, the duckbill platypus and spiny echidna, are
monotremes – they lay eggs.
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Zoogeographic regions, part 1
• Animals’ distribution patterns more complex and
irregular because of their mobility.
– The broad distributions of animals nevertheless do reflect a
general distribution of energy and food diversity.
• Nine zoogeographic regions are generally recognized.
– They represent average conditions and cannot portray some
common pattern in which different groups of animals fit
precisely.
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Zoogeographic regions, part 2
• Ethiopian Region
– The Ethiopian region has the most diverse vertebrate fauna
and greatest number of mammalian families.
• Oriental Region
– The Oriential region is similar to Ethiopian but with less
diversity (save for birds and reptiles; large number of
venomous snakes).
• Palearctic Region
– The Palearctic region has a poorer fauna than the previous
two, probably function of its higher latitudes and more
severe climate.
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Zoogeographic regions, part 3
• Nearctic Region
– The Nearctic region’s faunal assemblage relatively poor
(save for being well-represented with reptiles).
– It is largely a transitional zone between Palearctic and
Neotropical groups.
– It is very similar to the Palearctic, so that some group the
two together into a superregion, Holoarctic.
– The Nearctic reflects how faunal dispersal occurred via
Bering land bridge in geologic past.
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Zoogeographic regions, part 4
• Neotropical Region
– The Neotropical reigon has a rich and distinctive faunal
assemblage:
– It has a variety of habitats and is isolated from other
regions;
– The Neotropical has a larger number of endemic mammal
families than any other region;
– The region’s bird fauna is exceedingly diverse and
conspicuous.
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Zoogeographic regions, part 5
• Australian Region
– The Australian region has the most distinctive fauna of any
region.
– The lack of diversity is made up for by the animals’
uniqueness.
• Madagascar Region
– The Madagascar region is dominated by a relic assemblage
of unusual forms, including primitive primates (lemurs).
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Zoogeographic regions, part 6
• New Zealand Region
– The New Zealand region is characterized by a great
diversity of birds, many of which are flightless.
– The region has no native mammals and few amphibians
and reptiles.
• Pacific Region
– The Pacific region is characterized by extremely isolated
islands and island groups with limited biodiversity.
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