Geographic Ecology Chapter 22 1

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Outline • • • • • Introduction Island Area, Isolation, and Species Richness  Terrestrial  Aquatic Equilibrium Model of Island Biogeography Latitudinal Gradients in Species Richness Historical and Regional Influences 4

Introduction •

MacArthur

defined geographic ecology as the search for patterns of plant and animal life that can be put on a map.

 Above level of landscape ecology.

 Vast breadth  Chapter only focuses on a few aspects.

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Island Area, Isolation, and Species Richness •

Preston

found fewest bird species live on smallest islands and most species on largest islands.

•

Nilsson et al.

found island area was best single predictor of species richness among woody plants, carabid beetles, and land snails.

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Island Area, Isolation, and Species Richness 7

• Habitat Patches on Continents: Mountain Islands As Pleistocene ended and climate warmed, forest and alpine habitats contracted to the tops of high mountains across American Southwest.

 Woodlands, grasslands, and desert scrub, invaded lower elevations.

 Once continuous forest converted to series of island-like fragments associated with mountains: Montane.

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Lakes as Islands • Lakes can be considered as habitat islands.

 Differ widely by degree of isolation.

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Tonn

and

Magnuson

found the number of species increases with the area of an insular environment.

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Marine Islands • •

MacArthur

and

Wilson

found isolation reduces bird diversity on Pacific Islands.

Island area and species richness in Azore Islands:  Birds show clear influence of isolation on diversity, pteridophytes do not.

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Marine Islands 12

Isolation and Habitat Islands on Continents •

Lomolino et al.

found a strong negative relationship between isolation and the number of montane mammal species living on mountaintops across the American Southwest.

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Equilibrium Model of Island Biogeography •

MacArthur

and

Wilson

: Model explaining species diversity on islands = immigration and extinction rates.

 Rates of immigration highest on new island with no organisms.

 As species accumulate, rate of immigration declines since fewer arrivals arenew species.

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Equilibrium Model of Island Biogeography 16

Equilibrium Model of Island Biogeography • Rate of extinction rises with increasing number of species on an island for three reasons:  More species creates larger pool of potential extinctions 17

Equilibrium Model of Island Biogeography • Rate of extinction rises with increasing number of species on an island for three reasons:  More species creates larger pool of potential extinctions  As number of species increases, population size of each must diminish 18

Equilibrium Model of Island Biogeography • Rate of extinction rises with increasing number of species on an island for three reasons:  More species creates larger pool of potential extinctions  As number of species increases, population size of each must diminish  As number of species increases, competitive interactions between species will increase 19

Equilibrium Model of Island Biogeography • • Point where two lines cross predicts the number of species on island Rates of extinction determined mainly by island size:  Large near islands = highest S  Small far islands = lowest S  Small near and Large = intermediate S 20

Equilibrium Model of Island Biogeography 21

Species Turnover on Islands • Equilibrium model predicts species composition on islands is dynamic  Change = species turnover •

Diamond

: birds on 9 CA Channel Islands in stable equilibrium  Species turnover result of equal levels of immigration and extinction 22

Species Turnover on Islands 23

Experimental Island Biogeography •

Simberloff

and

Wilson

studied insect recolonization in Florida Keys  Chose 2 stands of mangroves as control islands; 6 others as experimental islands  Defaunated islands  Followed recolonization for 1 yr – Species number constant, but composition changed considerably 24

Spray insecticide on 2 islands, 6 no spray 25

Experimental Island Biogeography 26

Manipulating Island Area •

Simberloff

tested effect of island area on species richness = cut mangroves out  area reduced, S decreased  control island S increased slightly  reduced area < species  Area has positive influence on S 27

Simberloff (1976) Manipulating Island Area 28

Latitudinal Gradients in Species Richness

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Latitudinal Gradients in Species Richness • Most groups of organisms are more species rich in tropics • Brown grouped hypotheses into six categories: 30

•  1. Time Since Perturbation  More species in the tropics because tropics are older and disturbed less frequently  More time for speciation, less frequent disturbance reduces extinction rate 31

 2. Productivity  High productivity = high species richness (coral reefs, rainforests)  More energy to divide among population  3. Environmental Heterogeneity  More heterogeneity, more potential habitat areas and niches 32

 4. Favorableness  Tropics more favorable environments  No extremes to limit diversity  5. Niche Breadth and Interspecific Interactions  Various themes  Brown: biological processes play secondary role – Ultimate causes are physical differences 33

 6. Speciation rates and extinction rates  Tropics have increased speciation  Tropics have decreased extinction 34

Area and Latitudinal Gradients in Species Richness •

Rosenzweig:

immigration can be largely discounted at broad scales, thus speciation is primary source of new species 35

Area and Latitudinal Gradients in Species Richness •

Rosenzweig:

immigration can be largely discounted at broad scales, thus speciation is primary source of new species  Species removal via extinction  Tropics richness is greater due to higher rates of speciation and / or lower rates of extinction 36

Continental Area and Species Richness • Rosenzweig - strong positive relationship between area and species diversity 37

Map with real projection Tropics have higher area

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Historical and Regional Influences •

Latham

and

Ricklefs

: diversity of temperate zone trees cannot be explained by area effect  Temperate forest biome in Europe, Eastern Asia, and Eastern North America all have ~ similar area, but different levels of biological diversity  Eastern Asia: 3x NA and 6x Europe.

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Diversity of Temperate Trees •

Latham

and

Ricklefs

: Must examine conditions in these regions during last glacial period  Mountains in Europe form east-west oriented barriers  During last ice age, temperate trees had southward retreat largely cut-off  Lower species richness as consequence of higher extinction rate 41

Diversity of Temperate Trees •

Latham

and

Ricklefs

: Must examine conditions in these regions during last glacial period  Mountains in Europe form east-west oriented barriers  During last ice age, temperate trees had southward retreat largely cut-off 42

Historical and Regional Influences  Appalachian Mountains in N.A. run north south  temperate trees had retreat path as temperatures cooled  Also no mountain barriers in Asia 43

Historical and Regional Influences  Appalachian Mountains in N.A. run north south; temperate trees had retreat path as temperatures cooled.

 Also no mountain barriers in Asia.

• Most temperate tree taxa originated in Eastern Asia - dispersed to Europe and N.A.

 After dispersal lines were cut, speciation continued in Asia 44

Review • • • • • Introduction Island Area, Isolation, and Species Richness  Terrestrial  Aquatic Equilibrium Model of Island Biogeography Latitudinal Gradients in Species Richness Historical and Regional Influences 45

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