ecology slides

8/11/2019 Ecology slides

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Bio 356 announcements

Lab meets Wednesday at the UnionBay Natural Area

Field class 7 due Wednesday

Field class 8 due MONDAY at 5 pmin Kincaid 516

Office hours: Monday 9-10 and 1-3in Kincaid 516



What are the biodiversity consequences of habitat loss?

Thomson et al. 2003

Area A

If half of a habitat is lost or transformed, what fraction ofthe species are expected to go extinct?•Half•More than half•Less than half



Biology 356: Lecture #11

Spatial Ecology



Dec4• Introduction to spatial ecology

• Landscape fragmentation consequences

• Island biogeography



Levels of ecological study

IndividualsPopulations

Communities

Ecosystems

Landscapes

Physiological EcologyPopulation Ecology

Species InteractionsBiodiversity

Community EcologyEcosystem Ecology

Spatial Ecology



• A landscape is a heterogeneous area consistingof distinctive patches.



• A landscape is a heterogeneous area consistingof distinctive patches.• A patch is a contiguous area of a defined habitat.



• A landscape is a heterogeneous area consistingof distinctive patches.• A patch is a contiguous area of a defined habitat.• The matrix is the area between patches.• A corridor is a strip of habitat connecting twopatches.



• A landscape is a heterogeneous area consistingof distinctive patches.• A patch is a contiguous area of a defined habitat.• The matrix is the area between patches.• A corridor is a strip of habitat connecting twopatches.

•Edge : border between two contrasting habitats



Patch shape: Edge (perimeter) depends on rulerlength and fractal geometry

Relatively long ruler (scale) generates relatively shortedge



Patch shape: Edge (perimeter) depends on rulerlength and fractal geometry

Relatively short ruler (scale) generates relatively longedge



• Patch shape: S =

Patch shape: Shape depends on perimeter relative toarea



Patch shape

S =

S = Patch shapeP = Patch perimeter

A = Patch area

Which habitat has thegreater value of S?

a)

b)



Patch shape

S =

S = Patch shapeP = Patch perimeter

A = Patch area

Which habitat has thegreater value of S?

a)

b)

Patch shape is the ratio of patch perimeter to theperimeter of a circle with an area equal to patch area.



Lab preview

Record species composition of invertebrates under

each plywood“

island”

at UBNA



Lab preview

Define: patch, matrix, area, perimeter (edge), shape,

corridors



Lab preview

How does plywood“

island”

area affect speciesrichness?Does the density of a given species change with area?



• A landscape is a heterogeneous area composedof ecosystems that form distinctive patches.

• Landscape structure includes the area, shape,composition, and position of patches in a

landscape.

• Landscape structure influences the flow ofenergy, materials, and species across a landscape.

Introduction to spatial ecology: conclusions



How do abundance and diversity change with area?

Thomson et al. 2003

Area A



Species abundance increases with area

# butterflies(individuals)

d d l h



But species density declines with area

Patch area (m 2)

butterfly density(individuals / m 2)

# butterflies(individuals)

Low density ina small area =too fewindividuals topersist

S i i h i i h



Species richness increases with area

# of birdspecies

Species-arearelationships are log-log plots

logS = logc + b logA

b~ 0.25-0.4

S i i h i i h




# of birdspecies

On linear axes, fewerspecies are addedwith each increment of

areaS = c A b

b~ 0.25-0.4

S i i h i i h




# of birdspecies If half of a habitat is

lost or transformed,

what fraction of thespecies are expectedto go extinct?•Half

•More than half•Less than half

L d f i l i



• Species richness increases with patch area,while species density declines.

• Human activity has fragmented habitatsworldwide. For b=0.25, loss of 50% of area predicts16% extinction. For b=0.4, loss of 50% of area

predicts 24% extinction.

Landscape fragmentation: conclusions






Wh d i i h i ith ?



Why does species richness increase with area?

Potential mechanisms:• Species coexist better on large islands, wheredensities are lower.

• Island size correlates with heterogeneity; largerislands support species with different habitatrequirements.

• Island biogeography: Island size and proximityinfluence colonization and extinction rates



Eq ilib i th f i l d bi g g h



Immigration rate(species / time)

Equilibrium theory of island biogeography

# species present

When few species are present, each immigrant islikely to represent a new species; when manyspecies are present, immigrants are less likely torepresent new species.





# species present

When many species are present:• there is a larger pool of potential extinctions• the population size of each species mustdecrease, increasing the likelihood of extinction• competitive interactions are more likely

Extinction rate(species / time)





# species present



Change in species richness =rate of immigration - rate of extinction

Dynamic equilibrium of species richness whenimmigration rate = extinction rate





near

far

# species present


Proximity to other islands increases immigration rate.





small

large


# species present

Extinction rate decreases with island size.




small

large

small, far

large, farsmall, near

large, near


near

far

# species present



Species turnover



Species turnover

Dynamic equilibrium species richness doesnot always have the same speciescomposition

Turnover = Dis-similarity in speciescomposition

Experimental work on island biogeography




Simberloff and Wilson




• Experimental islands fumigated






Time (days)

# speciespresent

Near

Far

Proximity to other islandsincreased immigration rate.


Composition: species arrive and go extinct



Composition: species arrive and go extinct

Species richness: 20 2 14 17

Island biogeography: conclusions



• Island biogeography theory predicts that species richnessis a dynamic balance of immigration and extinction rates.Immigration rate depends upon proximity to otherislands, and extinction rate depends upon island size.

• Species composition on islands is expected to changeover time, even if species richness is at a dynamicequilibrium. Species turnover is also likely in space – islandswith similar species richness can have different composition.

Island biogeography: conclusions

ecology slides

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