Biodiversity in Biodiversity in PerspectivePerspective

Chapter 27Chapter 27

Easter IslandEaster Island

165 km165 km22 island in Polynesia island in Polynesia

Hundreds of massive stone statuesHundreds of massive stone statues

When Europeans first visited in 1722, When Europeans first visited in 1722,

the population was small and there the population was small and there

was little vegetationwas little vegetation

Easter Island HistoryEaster Island History

Colonized around 350 A.D.Colonized around 350 A.D.

Island was fertile and densely forestedIsland was fertile and densely forested

By 1400, soil fertility and crop yields By 1400, soil fertility and crop yields

had declinedhad declined

By 1550, the forests were all goneBy 1550, the forests were all gone

Food scarcity led to warfareFood scarcity led to warfare

Loss of BiodiversityLoss of Biodiversity

On Easter Island, 15,000 people nearly On Easter Island, 15,000 people nearly totally destroyed the biodiversity upon totally destroyed the biodiversity upon which they dependedwhich they depended

Today, there are six billion people on Today, there are six billion people on Earth and global biodiversity is Earth and global biodiversity is decliningdeclining

A worldwide extinction crisis is in the A worldwide extinction crisis is in the makingmaking

Biodiversity & ExtinctionBiodiversity & Extinction

90 percent of all species that have 90 percent of all species that have

ever lived are now extinctever lived are now extinct

Biodiversity is greater than everBiodiversity is greater than ever

Current range of biodiversity is the Current range of biodiversity is the

result of past extinctions and result of past extinctions and

recoveriesrecoveries

Mass ExtinctionsMass Extinctions

There have been five great mass There have been five great mass

extinctionsextinctions

Causes of mass extinctions are not Causes of mass extinctions are not

always clearalways clear

– Asteroid hit Earth at the K-T boundary, Asteroid hit Earth at the K-T boundary,

but many species were already in but many species were already in

declinedecline

Slow RecoveriesSlow Recoveries

Each mass extinction has been followed by Each mass extinction has been followed by

an adaptive radiationan adaptive radiation

Biodiversity recovers very slowlyBiodiversity recovers very slowly

It takes 20 million to 100 million years to It takes 20 million to 100 million years to

reach the pre-mass extinction level of reach the pre-mass extinction level of

diversitydiversity

Patterns in Some LineagesPatterns in Some Lineages

CENOZOIC

MESOZOIC

PALEOZOIC

CENOZOIC

MESOZOIC

PALEOZOIC

PROTOZOANS TRILOBITESBONY FISHES AMPHIBIANS REPTILES BIRDS MAMMALS

GYMNOSPERMSANGIOSPERMS (flowering plants)

INSECTS

(mammalian diversity for ten families studied)

Figure 27.2Page 476

Dead as a DodoDead as a Dodo Flightless bird lived on the island of Flightless bird lived on the island of

MauritiusMauritius

Killed off by EuropeansKilled off by Europeans

Once the dodo was extinct, a native Once the dodo was extinct, a native tree stopped reproducingtree stopped reproducing

May have coevolved with dodoMay have coevolved with dodo

Humans and Humans and Mammalian DiversityMammalian Diversity

Humans began hunting mammals Humans began hunting mammals

about 2 million years agoabout 2 million years ago

About 11,000 years ago, they began to About 11,000 years ago, they began to

drastically reduce mammalian habitatdrastically reduce mammalian habitat

Of the 4,500 living mammal species, Of the 4,500 living mammal species,

300 (6.7 percent) are endangered300 (6.7 percent) are endangered

Endangered SpeciesEndangered Species

An endemic species that is An endemic species that is

extremely vulnerable to extinctionextremely vulnerable to extinction

– EndemicEndemic means a species originated means a species originated

in one geographic region and is in one geographic region and is

found nowhere elsefound nowhere else

Threatened RegionsThreatened Regions

Critically endangered species

Threatened species

Relatively stable species; populations intact

Figure 27.4Page 478

Habitat LossHabitat Loss

Physical reduction of suitable places to Physical reduction of suitable places to

live, as well as loss of habitat as a live, as well as loss of habitat as a

result of chemical pollutionresult of chemical pollution

In the U.S.:In the U.S.:

– 98 percent of tallgrass prairies are gone98 percent of tallgrass prairies are gone

– 50 percent of wetlands have been 50 percent of wetlands have been

destroyeddestroyed

Habitat FragmentationHabitat Fragmentation

Habitats are chopped up into patchesHabitats are chopped up into patches Three effects:Three effects:

– Increases habitat edgesIncreases habitat edges– Decreases number of individuals that Decreases number of individuals that

can be supported; may be too few to can be supported; may be too few to allow breedingallow breeding

– Decreases the area in which individuals Decreases the area in which individuals can find food or other resourcescan find food or other resources

Island BiogeographyIsland Biogeography

Study of the factors affecting Study of the factors affecting

diversity on islandsdiversity on islands

Has implications for predicting Has implications for predicting

extinction of nonisland speciesextinction of nonisland species

Isolated patches of habitat are like Isolated patches of habitat are like

islandsislands

MacArthur-Wilson ModelMacArthur-Wilson Model

Uses island biogeography to Uses island biogeography to estimate future extinctionsestimate future extinctions

Model predictsModel predicts– Destruction of 50 percent of a habitat Destruction of 50 percent of a habitat

island will drive 10 percent of endemic island will drive 10 percent of endemic species to extinctionspecies to extinction

– Destruction of 90 percent of a habitat Destruction of 90 percent of a habitat island will drive 50 percent of species island will drive 50 percent of species to extinctionto extinction

Indicator SpeciesIndicator Species

Species that provide warning of Species that provide warning of changes in habitat and impending changes in habitat and impending widespread loss of biodiversitywidespread loss of biodiversity

Example:Example:– Migratory birds that breed in N. America Migratory birds that breed in N. America

and winter over in tropical forestsand winter over in tropical forests– Study found populations are plummeting as Study found populations are plummeting as

a result of deforestation, habitat a result of deforestation, habitat fragmentationfragmentation

Exotic SpeciesExotic Species

Species that have been introduced into Species that have been introduced into a habitat, either deliberately or a habitat, either deliberately or accidentallyaccidentally

Exotic species often have characteristics Exotic species often have characteristics that allow them to outcompete endemic that allow them to outcompete endemic speciesspecies

Play a role in 70 percent of cases where Play a role in 70 percent of cases where endemic species are threatenedendemic species are threatened

Hunting and WhalesHunting and Whales

humpback whale

sperm whale

sei whale

fin whale

blue whale

other species

Figure 27.6Page 479

Distribution of Coral ReefsDistribution of Coral Reefs

Coral reefs

Localities for solitary corals

Deep-water coral banks or thickets

Restricted 21°C (70°F) isotherm Figure 27.7Page 480

Threats to Coral ReefsThreats to Coral Reefs

Natural threats, such as hurricanesNatural threats, such as hurricanes

Man-made threatsMan-made threats– Water pollution, oil spillsWater pollution, oil spills

– Dredging Dredging

– Dynamite and cyanide fishingDynamite and cyanide fishing

– Coral bleachingCoral bleaching

Coral BleachingCoral Bleaching

Reef-building corals have photosynthetic, Reef-building corals have photosynthetic,

dinoflagellate symbiontsdinoflagellate symbionts

When stressed, corals expel the protistansWhen stressed, corals expel the protistans

If the stress persists, the coral dies, If the stress persists, the coral dies,

leaving its bleached hard parts behindleaving its bleached hard parts behind

Coral bleaching may be an effect of global Coral bleaching may be an effect of global

warming and increased sea temperatureswarming and increased sea temperatures

Rachel CarsonRachel Carson

Oceanographer and marine biologistOceanographer and marine biologist

Published Published Silent SpringSilent Spring in 1962 in 1962

– Described the harmful effects of Described the harmful effects of

pesticides on songbirds and other pesticides on songbirds and other

speciesspecies

Book helped launch the Book helped launch the

environmental movementenvironmental movement

Conservation BiologyConservation Biology

Systematic study of biodiversitySystematic study of biodiversity

Works to elucidate the evolutionary Works to elucidate the evolutionary

and ecological origins of biodiversityand ecological origins of biodiversity

Attempts to identify ways to maintain Attempts to identify ways to maintain

biodiversity for the good of human biodiversity for the good of human

populationspopulations

Identifying Hot SpotsIdentifying Hot Spots

A global survey of biodiversity is A global survey of biodiversity is impossibleimpossible

Researchers are identifying habitats Researchers are identifying habitats where many endemic species are where many endemic species are facing extinction facing extinction

Regional data is pooled to create a Regional data is pooled to create a global inventory of biodiversityglobal inventory of biodiversity

What’s It Worth?What’s It Worth?

Economic analysis can assign future Economic analysis can assign future value to ecoregionsvalue to ecoregions

Successful conservation requires that Successful conservation requires that sustaining biodiversity have greater sustaining biodiversity have greater economic value than destructioneconomic value than destruction

Biodiversity may have future Biodiversity may have future economic value as a source of economic value as a source of medications or chemical products medications or chemical products

People versus BiodiversityPeople versus Biodiversity The main threat to biodiversity is The main threat to biodiversity is

growth of human populations growth of human populations Many poor people must now choose Many poor people must now choose

between the good of endangered between the good of endangered species and the good of their families species and the good of their families

People will sustain biodiversity when People will sustain biodiversity when they can make a living by doing sothey can make a living by doing so

Strip LoggingStrip Logging

Allows tropical woods to be logged in Allows tropical woods to be logged in a profitable, sustainable waya profitable, sustainable way

Sloped forested area is logged in Sloped forested area is logged in strips, working up the slopestrips, working up the slope

Runoff from logged areas flows to Runoff from logged areas flows to regenerating forest, enhancing its regenerating forest, enhancing its growthgrowth

Strip LoggingStrip Logging

uncut forest

cut 1 year agodirt road

cut 3-5 years ago

cut 6-10 years ago

uncut forest

stream

Figure 27.12Page 484

Riparian ZonesRiparian Zones

Narrow corridors of vegetation along Narrow corridors of vegetation along streams or riversstreams or rivers

Rich in endemic speciesRich in endemic species In the American West, cattle have In the American West, cattle have

destroyed most riparian vegetationdestroyed most riparian vegetation Rotating cattle away from riparian Rotating cattle away from riparian

zones saves endemic species and zones saves endemic species and provides richer grazingprovides richer grazing