GEO 200: Physical Geography Terrestrial Biota (1 of 2)

GEO 200: Physical Geography

Terrestrial Biota (1 of 2)

Rev. 25 April 2006 Terrestrial Biota 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?


Natural distributions

• Four conditions determine the natural distribution of any species or group of organisms:– Evolutionary development

– Migration/dispersal

– Reproductive success

– Extinction


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.




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.





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.



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.




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.


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.


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.


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.



Adaptations of plants, part 2

• Hygrophytic adapatation– A hygrophyte is a plant that requires a saturated or semi-

saturated 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.




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.


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.



• 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.



• 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.



• 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.



• 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.



• Categorizing by supposed structure (this works for foresters, but not geographers)– Hardwoods are angiosperm trees that are usually broad-

leaved 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.



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.



• 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.



• 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.



• 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.




• 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.




• 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.





• 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.



• 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.





• Elevational changes (continued)– Vertical zonation (continued)

• Southern and Northern hemispheres experience different elevation-latitude relationship, with the Southern Hemisphere having lower treelines.

• The reason for the discrepancy is not understood yet.




• 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.



• 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.




• 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.



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.


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


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.




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.


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.


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.


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.



• 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.



• 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.



• 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.


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.



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.


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.



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).


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.





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.




• 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.



• 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.




• 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.



• 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).



• 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.

Documents

GEO 200: Physical Geography Terrestrial Biota (1 of 2)