introduction – landscape ecology

Introduction – Landscape Ecology

• Landscape Ecology: Study of landscape structure and processes.– Landscape: Heterogeneous area composed of

several ecosystems.– Landscape Elements: Visually distinctive

patches in an ecosystem.

Vancouver Island marmot(Marmota vancouverensis)

Isolated from hoary and Olympic marmots

~100 left

Vancouver Island marmot(Marmota vancouverensis)

Natural tree succession

Vancouver Island marmot(Marmota vancouverensis)

• Logging – disjunct patches- max. dispersal = 7 km

• Climate• Prey-Predator Dynamics

Human Land Use Practices 1) Agriculture2) Suburban Development

Let’s pick on Indiana:

• 97% of land in state = privately-owned

• In central Indiana, • 70+% of land in row crop• <10% in forest• Urban sprawl intensifying

Human Impacts Ecosystem simplification: elimination of

species from food webs via human alterations to land

Example: vertebrate communities in ag. landscapes

Intensive Agriculture&

Clean Farming

Timber Extraction&

Fragmentation

Roads: Formation of Barriers in Landscapes

Formation of Terrestrial “Islands”

Habitat Fragmentation • Process of breaking contiguous unit into

smaller pieces; area & distance components

• Leads to:

< remnant patch size

> edge:interior ratios

> patch isolation

< connectivity• Community & Ecosystem processes

altered

Formation of Terrestrial “Islands”

Habitat Loss vs. Habitat Fragmentation

#patches

Patch isolation

Patch size

Edge

What about aquatic systems?

What about aquatic systems?Con.Bio 12(6)

Habitat Fragmentation • area-sensitive species: species that

require minimum patch size for daily life requirements

• Edge effects: influence of factors from outside of a patch

Increased Edge Habitat

Increased Edge Habitat

Edge Effects • Habitat surrounding a patch can:

- change abiotic conditions; e.g., temp.

- change biotic interactions, e.g., predation

Example of nest predation = edge effect of approximately 50 m into forest patch

Habitat Fragmentation • First-Order Effects: fragmentation leads

to change in a species’ abundance and/or distribution

Habitat Fragmentation • Higher-Order Effects: fragmentation

indirectly leads to change in a species abundance and/or distribution via altered species interactions

Predators- Abundance- Distribution- Foraging Behaviors

Avian Competitors Avian Prey

Brood Parasites

HABITAT FRAGMENTATION

Ground-Nesting Birds- Abundance - Distribution

Parasites- Abundance- Distribution

REPRODUCTIVE SUCCESS

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Habitat Fragmentation: Species-Specific Sensitivity?

• Rare species = more vulnerable

• Wide ranging species = large-area requirements

• Species with reduced mobility = more vulnerable

• Species with low fecundity (related to rarity?)

• Species with short life cycle (or multi-stage life cycle?)

Habitat Fragmentation: Species-Specific Sensitivity?

• Ground-nesting birds may be more vulnerable (30-60% reduction in last 25 yrs)

• Interior-dependent species

• Species vulnerable to human exploitation or disturbance

• Specialist species?

Habitat Fragmentation: Species-Specific Sensitivity?

Generalizations are a good start

(= hypotheses?), but a little more complex than that……

Gehring and Swihart. 2003. Biological Conservation109:283-295

Spatial and TemporalEcology of Raccoons Gehring et al. In prep.

Swihart et al. 2003. Diversity and Distributions 9:1-8.

Brown and Litvaitis. 1995. Canadian Journal of Zoology 73:1005-1011

Implications of Changes in Scale

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PredatorPrey

Insects sampled at 10-m intervals for 100 m

Implications of Changes in Scale

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PredatorPrey

Insects sampled at 2000-m intervals for 20,000 m

Landscape Processes

• Landscape structure influences processes such as the flow of energy, materials, and species between the ecosystem within a landscape.

Landscape Structure and Dispersal of Small Mammals

Habitat Patch Size and Isolation and Density of Butterfly

Populations

Organisms and Landscape Structure

• African elephants knock down tress.– Change woodland to grassland.

• Kangaroo Rats dig burrow systems that modify soil structure and plant distributions.

• Beavers cut trees, build dams and flood surrounding landscape.– At one time, beavers modified nearly all

temperate stream valleys in Northern Hemisphere.

Organisms and Landscape Structure

• Johnston and Naiman documented substantial effects of beavers on landscape structure.– Over 63 yrs, area created by beavers increased

from 200 ha to 2,661 ha.– Changed boreal forest landscape to complex

mosaic.

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Organisms and Landscape Structure

• Beaver activity between 1927-1988 increased quantity of most major ions and nutrients in impounded areas. Three possible explanations:– Impounded areas may trap materials.– Rising waters captured nutrients formally held in

vegetation.– Habitats created by beavers may promote nutrient

retention by altering biogeochemical processes.

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Introduction – Geographical Ecology

• MacArthur defined geographical 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.

Oceanic Island = Terrestrial Island ?????

Island Area 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 and Species Richness

Species-Area Relationship

S = cAz

S = # of species

A = island area

• Positive correlation between island size & number of species

• Applies to terrestrial “islands” also

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.

• Tonn and Magnuson found the number of species increases with the area of an insular environment.

• Barbour and Brown found positive relationship between area and fish species richness.

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Lakes as Islands

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Marine Islands• MacArthur and Wilson found isolation reduces bird

diversity on Pacific Islands.• Williamson summarized data from relationship

between island area and species richness in Azore Islands:– Birds show clear influence of isolation on diversity, ferns

do not.– Land birds fly across water barriers, and ferns produce

large quantities of light spores easily dispersed in the wind.

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Marine Islands

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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 patterns of species diversity on islands as result of immigration and extinction rates.– Reasoned rates of immigration would be

highest on new island with no organisms.• As species began to accumulate, rate of immigration

would decline since fewer arrivals would be new species.

Equilibrium Model of Island Biogeography

• Predicted rate of extinction would rise with increasing number of species on an island for three reasons:– Presence of more species creates a larger pool of

potential extinctions.– As number of species increases, population size of

each must diminish.– As number of species increases, potential for

competitive interactions between species will increase.

Equilibrium Model of Island Biogeography

• Point where two lines cross predicts the number of species that will occur on an island.

• Proposed rates of extinction on islands would be determined mainly by island size.– LG near islands will support highest number.– SM far islands will support lowest number.– SM near and LG far will support intermediate number.

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Island Biogeography

• equilibrium model suggesting that the number of species occurring on an island represents a balance between immigration (in) and extinction (out)

• Robert MacArthur & E.O. Wilson

Experimental Island Biogeography

• Simberloff and Wilson studied insect recolonization in Florida Keys.– Chose 2 stands of mangroves as control islands,

and 6 others as experimental islands.• Defaunated islands

– Followed recolonization for 1 yr.

» Species number stayed constant, but composition changed considerably.

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Experimental Island Biogeography

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Colonization of New Islands by Plants

• Rydin and Borgegard found variation in spp. richness correlated positively with island area and accounted for 44-85% of variation in species richness among islands.– Small and medium islands continued to accumulate

species.– Large islands attained equilibrium of immigration and

extinction.• Difficult to separate effects of habitat diversity from area

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Manipulating Island Area

• Simberloff tested effect of island area on species richness.– In all cases where area was reduced, species

richness decreased.• Richness on control island increased slightly.

– Islands with reduced area lost species with each reduction in area.

• Showed area has positive influence on species richness.

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Manipulating Island Area

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Island Biogeography Update

• Brown and Kodric-Brown found higher immigration rates to near islands can reduce extinction rates.

• Lomolino found island area can have a significant effect on immigration rates.

• Area and isolation are only two of several environmental factors affect island species richness.

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Latitudinal Gradients in Species Richness

• Most groups of organisms are more species-rich in the tropics.

• Brown grouped hypotheses into six categories:

– Time Since Perturbation• More species in the tropics because tropics are older and

disturbed less frequently.– More time for speciation, and less frequent disturbance reduces

extinction rate.

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Latitudinal Gradients in Species Richness

– Productivity• High productivity contributes to high species

richness.– More energy to divide among population.

– Environmental Heterogeneity• More heterogeneity, thus more potential habitat

areas and niches.

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Latitudinal Gradients in Species Richness

– Favorableness• Tropics have more favorable environments.

– No extremes to limit diversity.

– Niche Breadth and Interspecific Interactions• Various themes

– Brown suggests biological processes must play secondary role.

» Ultimate causes must by physical differences.

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Area and Latitudinal Gradientsin Species Richness

• Rosenzweig proposed immigration can be largely discounted at broad scales, thus speciation will be 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.

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Continental Area and Species Richness

• Rosenzweig found a strong positive relationship between area and species diversity.

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