Patterns in space

Log areaLog

spe

cies

num

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productivity

# sp

ecie

s

Habitat variety

# sp

ecie

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Latitude

# sp

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mainland

Log area

Log

spe

cies

num

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close farislands

Time during successionSpe

cie

s nu

mbe

r

Disturbance frequencySpe

cie

s nu

mbe

r

Millions of years

Spe

cie

s nu

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Patterns in time

Hundreds of Millions of years

Spe

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Trophic level

# sp

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Two more patterns

Body size within taxon

# sp

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1) Why do species numbers increase with area?

Log areaLog

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cies

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PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

When sampling area is increased, more habitats

will be incorporated.

More habitats support more habitat specialists

More habitats can serve as refuge.

Co-evolution of competitors (niche separation).

Universality of spatial variability.

Metapopulation theory (more demes, more safety).

Sites are spatially heterogeneous at many scales.

Texas by Annual Precipitation

2) Diversity generally increases with productivity.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Higher productivity supports more individuals

(biomass). Therefore, more species can attain

the minimal viable population size.

Most productive environments exclude weak competitors??

Makes some PP relationships unstable??

Minimal viable population size (through demographic stochasticity, Allee effects, genetic drift).

productivity

# sp

ecie

s

Competitive exclusion principle.

Paradox of enrichment.

Climate dominates site productivity, the interplay of precipitation and temperature.

However, climate factors alone do not explain all patterns between ecosystem productivity and biodiversity.

3) A more spatially variable habitat has more species per area.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Habitat variety

# sp

ecie

s

More habitats support more habitat specialists.

Co-evolution of competitors (niche separation).

4) Biodiversity decreases between the species-rich equatorial tropics and the species-poor polar regions.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Latitude

# sp

ecie

s

Higher productivity supports more individuals

(biomass), therefore, more species.

Minimal viable population size (through demographic stochasticity, Allee effects, genetic drift).

Mercator projection

Equal-area projection

John Terborgh recognized (1973) that the tropics are the largest contiguous earth biome.

4) Biodiversity decreases between the species-rich equatorial tropics and the species-poor polar regions.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Latitude

# sp

ecie

s

Higher productivity supports more individuals

(biomass), therefore, more species.

The tropics are larger than any another biome, therefore species have

lower extinction rates and more opportunities for

speciation.

Larger ranges are bigger targets for geographical barriers (speciation).

Minimal viable population size.

Metapopulation theory (more demes, more safety).

5) Higher trophic levels have fewer species.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Trophic level

# sp

ecie

s

Lower productivity supports fewer individuals

(biomass), therefore, fewer species.

Longer food chains are more unstable.

Tendency of predator-prey interactions to cycle.

Minimal viable population size.

6) Islands have fewer species than mainlands.7) Farther islands have fewer species than closer islands.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Species numbers on islands are regulated through the rates of immigration (from

mainland) and local extinction.

Farther islands have reduced immigration rates.

Islands do not have sink species.

Metapopulation dynamics. Species numbers are at equilibrium (extinction rates = immigration rates).

Source-sink populations.

mainland

Log area

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cies

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close farislands

Imm

igra

tion

rate

E

xtinction rate

Species number S

I

P

ESS

dt

dS

Island Biogeography(Robert MacArthur and Edward Wilson)

Imm

igra

tion

rate

E

xtinction rate

Species number S

I

P

E

S*

S* is a stable species number.

However: species on islands constantly turn over. S* is constant through the balance of extinctions and immigrations

Imm

igra

tion

rate

E

xtinction rate

Species number S

I

P

E

S1*

Farther islands have fewer species because immigrations occur less often.

S3* S2*

Island distance from mainland increases

Imm

igra

tion

rate

E

xtinction rate

Species number S

I

P

E

S1*

Larger islands have lower extinction rates than smaller islands (because population sizes are larger).

S3*S2*

Island size increases

Imm

igra

tion

rate

E

xtinction rate

Species number S

I

P

E

Supertramps get there first: species may have different dispersal and colonization abilities.

S*

Extinction rate accelerates with species number: some species may begin to compete or some species may eat another to extinction upon arrival.

Imm

igra

tion

rate

E

xtinction rate

Species number S

I

P

E

S*

Mangrove islands, Florida Keys

Daniel Simberloff tested MacArthur and Wilson’s hypothesis on mini-islands off the Florida coast:

arthopods

Do species turn over? – Yes.

In 1970, Simberloff defaunated four small islands.

Islands: Years 0-1 Years 1- 2 Years 2-3

E1 0.100 0.194 0.219

E2 0.196 0.263 0.239

E3 0.190 0.225 0.250

ST2 0.395 0.514 0.341

Species held in common between the time before defaunation and subsequent censuses (as fractions):

Does island size affect species number? – Yes.

Simberloff reduced island size, by cutting down mangrove trees and counted species before and one year after.

8) Diversity increases during succession.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Only a few early successional species

(plants) can deal with the harsh conditions. They

pave the way for (presumably more) later

successional species.

Facilitation model of succession: early successional species pave the way (i.e. create niches) for late successional species.

Time during successionSpe

cie

s nu

mbe

r

9) Diversity is maximal with intermediate disturbance.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Local, mild disturbance creates a patchwork of

sites in various stages of succession.

Intermediate disturbance generates maximal habitat

diversity for a maximum number of species.

Gap model of succession.

Competition theory (more niches more species)

Disturbance frequencySpe

cie

s nu

mbe

r

10) Over millions of years, diversity stays constant.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Mainland diversity may (like island diversity) track a stable equilibrium where extinction rates balance

speciation rates.

Metapopulation theory (for the extinction part)

Co-evolution of competitors: empty niches tend to fill.Millions of years

Spe

cie

s nu

mbe

r w

ithin

tax

on

Spe

ciat

ion

rate

Extinction rate

Species number S

The more species, the more speciation events. Speciation is accelerated at low species densities, because there are more ecological opportunities.

The extinction rate increases, because, as the number of species in the province increases, more populations will become small and have an increased risk of extinction.

S*

Spe

ciat

ion

rate

Extinction rate

Species number S

Smaller provinces

Smaller continents have fewer species, because • extinction rates are higher • speciation rates lower.

Larger continents have more species

10) Over hundreds of millions of years, diversity increases.

PATTERN EXPLANATION ECOLOGICAL PRINCIPLES

Geologic and climate change opens new habitable spaces.

Evolutionary key innovations spark

evolutionary radiations of new families.

New niches come into existence with the arrival of key innovations.

Hundreds of millions of years

Num

ber

s of

fam

ilies

Adaptive radiation after the rise of key innovation.

Example: the hypocone in mammalian cheek teeth:

Evolved > 20 times independently during the last 65 Mio years.Groups with hypocone greatly diversified, groups without did not.

The hypocone improves the processing of plant materials.

No hypoconehypocone shelfhypocone