The Biosphere and Animal Distribution

Chapter 37

Earth Environment - OverviewWater has physical properties critical to life on

earth.

The steady supply of sunlight maintains a suitable range of temperatures for life metabolism.

Living matter requires a supply of major and minor elements available on earth.

The earth’s gravity is strong enough to hold an extensive gaseous atmosphere.

Earth EnvironmentThe environment is modified by organisms.

Organisms are adapted by evolution to the environment.

The earth is an open system with a continuous supply of energy.

Building materials for life come from producers and are cycled through consumers.

Life is part of a cycle of life-death-decay-recycling.

Earth EnvironmentThe primitive earth of

4.5 billion years ago had a reducing atmosphere of ammonia, methane, and water and was fit for pre-biotic synthesis of early living forms.This early

atmosphere would be fatal to today’s organisms.

The appearance of free oxygen in the atmosphere is an example of the reciprocity of life and the earth.

Living organisms produce changes in their environment and must adapt and evolve.

BiosphereThe biosphere

is the thin outer layer of the earth capable of supporting life.Includes living

organisms as well as the physical environments.

Biosphere - SubdivisionsLithosphere – rocky material of the earth’s outer shell.

Source of mineral elements required for life.

Hydrosphere – water on or near the earth’s surface.

Atmosphere – the gaseous component of the biosphere.Atmospheric oxygen is produced by photosynthesis.

Greenhouse EffectMaterials in the atmosphere, such as CO2 and

water vapor retain heat, raising atmospheric temperature.Greenhouse effectBurning fossil fuels increases CO2 in the

atmosphere.

Greenhouse EffectThe greenhouse effect provides conditions essential for

life on Earth.Humans are increasing this effect. Increased temperatures could lead to a rise in sea level

as polar ice melts.

BiomesVarying combinations of both biotic and abiotic factors

determine the nature of Earth’s many biomes.

Biomes are the major types of ecological associations that occupy broad geographic regions of land or water.

BiomesEach biome grades into the next – without sharp

boundaries.Boundary areas are called ecoclines.

Terrestrial BiomesClimate is particularly

important in determining why particular terrestrial biomes are found in certain areas.TemperatureRainfallSolar radiation

Terrestrial Biomes

The sun’s rays strike higher latitudes at a lower angle.Atmospheric

heating is less.

Terrestrial BiomesAir warmed at the equator rises and moves toward the

poles.

Replaced by cold air moving away from the poles.

Rotation of the earth complicates this pattern.Three latitudinal cells result.

Terrestrial BiomesHot, moist air rises at

equator, cools, condenses and provides rainfall (tropical forests).

Warm air flows northward, and sinks at 20-30° latitude – dry.

Air heats, absorbs moisture (desert areas), then the air flows toward the equator again.

The Distribution of Major Terrestrial Biomes

General Features of Terrestrial Biomes

Vertical stratification is an important feature of terrestrial biomes.CanopyLow-treeShrub understoryGround layerForest floor (litter

layer)

Temperate Deciduous ForestTemperate deciduous forests receive rain year-

round. Cold winters and hot, humid summers.Animals may migrate, hibernate, or survive on scarce

available food or stored fat through the winter.

Coniferous ForestConiferous forests, or taiga, are common in the

northern hemisphere. Evergreens dominantColder, less rain than temperate forests.

Coniferous ForestMammals that

inhabit coniferous forests include deer, moose, elk, snowshoe hares, wolves, foxes, lynxes, weasels, bears.Adapted for long,

snowy winters.

Tropical ForestTropical rain forests receive lots of rain and are

generally warm year-round.StratifiedDiverse

Tropical ForestCanopy – insectivorous birds and bats fly

above the canopy.Fruit bats, canopy birds, and mammals live in the

canopy eating leaves & fruit.

Middle zones are home to arboreal mammals (monkeys, sloths), birds, bats, insects, amphibians.Climbing animals move along the tree trunks feeding

at all levels.

Ground level contains larger mammals (capybara, paca, agouti, pigs) as well as a variety of reptiles and amphibians.

Tropical ForestNutrients in a tropical forest are tied up in living

organisms.Soil is poor.

Slash and burn agriculture involves removing vegetation to grow crops – but the soil is so poor that the fields must be moved often.

GrasslandTemperate grasslands receive seasonal

precipitation and have cold winters and hot summers.Prairie

GrasslandGrasses and herds

of large grazing mammals are dominant.Jackrabbits, prairie

dogs, and ground squirrels are common.

Predators include coyotes, cougars, bobcats, raptors, badgers, and ferrets.

GrasslandSavannas are tropical grasslands with seasonal

rainfall.

GrasslandChaparral receives highly seasonal rainfall.

Shrubs and small trees are common.Adaptations to fire.

TundraTundra has a permanently frozen layer of soil

called permafrost that prevents water infiltration.Very cold, short growing season.Little rain

TundraTundra is often covered with bogs, marshes, or ponds.Grasses, sedges, and lichens may be common.Lemmings, caribou, musk-oxen, arctic foxes, arctic

hares, ptarmigans and other migratory birds.

DesertDeserts have very low precipitation – less than 30

cm/yr.Variable temperatures.Animals often nocturnal and live in burrows.Reptiles and small mammals are common.

Aquatic Biomes

Aquatic BiomesAquatic biomes account for the largest part of the

biosphere in terms of area.Can contain fresh or salt water.

Oceans cover about 75% of Earth’s surface.Have an enormous impact on the biosphere.

Inland WatersOnly about 2.5% of the earth’s water is fresh.

Much of that is found in polar ice caps or underground aquifers.

Inland WatersLotic, or running water habitats include streams and

rivers.More oxygen

Lentic, or standing water habitats include lakes and ponds.Less oxygen

Inland WatersOligotrophic

lakes – nutrient poor & oxygen rich.

Eutrophic lakes – nutrient rich & sometimes oxygen poor.Eutrophication

An oligotrophic lake A eutrophic lake

LAKES

Inland WatersStreams and

rivers have a current.

STREAMS AND RIVERS

Inland WatersAnimals living in vegetation or debris of the bottom

(benthos) are called benthic.Snails, mussels, crustaceans, insects.

Animals up in the water column are pelagic.Swimming animals are called nekton.Floating or weak swimmers are called plankton.

WetlandsWetlands

include areas that are able to support aquatic plants.

May be freshwater or marine.

WETLANDS

EstuariesEstuaries are transition

areas between river and sea.Salinity varies from

nearly fresh to the salinity of seawater.

ESTUARIES

Aquatic BiomesMany aquatic biomes are stratified into zones

or layers defined by light penetration, temperature, and depth.The photic zone is the most productive.

Rocky Intertidal ZoneThe rocky intertidal zone is alternately

submerged and exposed by the tides.Upper zones are exposed to air longer.Physical stress (desiccation, waves, temp,

salinity), predation, and competition produce distinct bands.

Rocky Subtidal ZoneKelp forests

dominated by brown seaweeds occupy shallow subtidal waters.Grazing urchins

and molluscs are common.

Predators include sea stars, fishes, and otters.

Rocky Subtidal ZoneCoral reefs are

limited to the photic zone in tropical marine environments with high water clarity.Highly diverse

CORAL REEFS

Nearshore Soft SedimentsIntertidal and subtidal environments with soft sediments

include beaches, mudflats, salt marshes, sea-grass beds, and mangrove communities.

Nearshore Soft SedimentsSalt marsh habitat

includes grasses, mussels, crabs, shrimp, and polychaetes.Burrowing organisms.Deposit or filter

feeders.Small fishes and birds

that feed on them are common.

Nearshore Soft SedimentsCalm, tropical, coastal

areas support mangrove communities.Mangrove trees grow

submerged in soft sediments.

Rich community of detritus feeders (oysters, crabs, shrimp).

Many fishes – often used as a nursery ground.

Deep-Sea SedimentsThe deep sea includes the continental slope,

continental rise, and abyssal plain.Sand where there are currents, fine mud where currents

are weak.Suspension feeding invertebrates are common.Deposit feeders found in muddy areas.

Hydrothermal VentsHydrothermal vents occur on the abyssal plain in

areas of submarine volcanic activity.Archaebacteria that derive energy by oxidizing sulfides

form the basis of the food chain.Grazed by bivalves, limpets, and crabs.Other organisms, like tube worms, have symbiotic

archaebacteria.

Pelagic RealmThe pelagic realm includes the open ocean area.

High oxygen, low nutrient levels.Areas of upwelling bring nutrients up from the sea floor.

OCEANIC PELAGIC BIOME

Pelagic RealmEpipelagic – surface

waters

Mesopelagic – twilight zone, supports a varied community of animals.

Deep sea forms depend on a rain of organic debris from above.

ZoogeographyZoogeography describes patterns of animal

distribution and species diversity.Why species and species diversity are distributed as they

are.

ZoogeographyThe history of an animal species must be

documented before we can understand why it lives where it does.Camels originated in North America and spread to

Eurasia, Africa, and South America.Camels went extinct in North America 10,000 years

ago.Today, we see true camels in Eurasia & Africa and

camel descendents (llamas, alpacas etc) in South America.

ZoogeographyGeologic change is responsible for much of the

alteration in animal distribution.

ZoogeographyPhylogenetic systematics allows us to reconstruct

histories of animal distributions.Geographical distributions of closely related species are

mapped onto a cladogram to generate hypotheses of the geographic history.

ZoogeographyDisjunct distributions are closely related species that

live in widely separated areas.Dispersal – a population moves to a new location.Vicariance – environmental changes break up a once

continuous population into small pockets.

Distribution by DispersalDispersal involves emigration from one region and

immigration into another.One way outward movement.

Different from a periodic movement back & forth.

Active or passiveCenter of originExplains movement of animal populations into favorable

habitats adjacent to the place of origin.

Distribution by VicarianceAreas once joined may become separated by barriers.

Population becomes fragmented into smaller, isolated populations.

Lava flowsContinental driftEmergence of mountain ranges

Distribution by VicarianceVicariance by continental

drift helps to explain the disjunct distribution of ratite birds.Ancestral species

widespread throughout Southern Hemisphere.

Distribution by VicarianceAs the continents

moved apart, the ancestral species was fragmented into disjunct populations that evolved independently producing the diversity seen today.

Continental DriftThe concept of continental drift was proposed by

Alfred Wegener in 1912.Not fully accepted until the mechanism was found.

Continental DriftPlate tectonics is the mechanism of continental drift.

The earth’s surface is composed of 6-10 rocky plates which shift position on a more malleable underlying layer.

Continental DriftPangaea – the single great landmass – broke up 200

million years ago.Two supercontinents resulted:

Laurasia – North America, Eurasia, GreenlandGondwana – South America, Africa, Madagascar, Arabia,

India, Australia, New Guinea, Antarctica

Continental DriftContinental drift explains several puzzling distributions

of animals.Similarity between some organisms in South America and

Africa.

Continental Drift - The Case of Marsupial Evolution

Marsupials appeared about 100 million years ago in South America.

They spread through Antarctica and Australia that were at that time joined together.

Continental Drift - The Case of Marsupial Evolution

Marsupials encountered placental mammals in North America, could not compete, and became extinct. The modern opossums are recent arrivals from South America.

The placental mammals expanded into South America, but the marsupials were well established there.

About 50 million years ago, Australia drifted apart from Antarctica and remained in isolation with only marsupials to diversify on the continent.

Wallace’s LineWallace’s line

represents a geographic separation between Asian and Australian faunas.

A collision of tectonic plates brought formerly distant land masses closer together.

Temporary Land BridgesTemporary land bridges

have been important pathways for dispersal.Land bridge connected

Asia and North America across the Bering Strait.

Today, a land bridge connects North and South America

Climatic Cycles and Vicariance

Glacial cycles have occurred with durations of 20,000 to 100,000 years within the past three million years.

Taxa sharing the same areas typically differ greatly in evolutionary age and in phylogenetic branching pattern.

Climatic Cycles and Vicariance

Cycling temperatures interact with the habitat requirements of animals.