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Biogeo > Slideshow 11 > Flashcards

Slideshow 11 Flashcards

1
Q

Island types and formations (4 types)

A

continental islands
island arcs
hotspot islands
terranes and accretion

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2
Q

Continental Islands - Origin

A

part of a continental landmass

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3
Q

Continental Islands - Formation

A

separated by rising ocean levels (ex: Newfoundland, PEI, British Isles)

separated by tectonic processes (ex: Madagascar, New Zealand)

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4
Q

Island Arcs - Origin

A

Volcanic activity

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5
Q

Island Arcs - Formation

A

Old ocean crust is subducted, causing stresses nearby on the overlying plate; volcanic eruptions build new islands that rise above the seafloor

Ex: Islands of Japan, Lesser Sunda Islands

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6
Q

Hotspot Islands and Seamounts - Origin

A

Fixed hotspots scattered throughout the Earth’s mantle (ex: Yellowstone national park, Hawaii, Iceland)

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7
Q

Hotspot Islands and Seamounts - Formation

A

Volcanoes rise from the seafloor; the plate moves; a series of islands is born

Erosion reduces islands to seamounts (guyots)

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8
Q

Formation of an Island chain

A

Erosin flattens the tops of the islands and seamounts

Seamounts are ‘islands’ of incredible biodiversity - poorly known, destroyed by deep sea trawling

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9
Q

Hotspot Islands and Seamounts - bend

A

The bend in the Emperor Seamount - Hawaiian Islands chain is suggested to be caused by a change in direction of the movement of the Pacific plate about 43 MYA

similar bends are seen in other pacific island chain

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10
Q

Pacific Islands - types

A

All 3 types
Continental - New Zealand, New Caledonia

Island Arc - the Aleutians, the Kuriles

Hotspot Islands - Taumato Ridge, Archipelago, Hawaiian Islands

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11
Q

Terranes

A

a small area where geology is different from surrounding regions

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12
Q

Accreted terrane

A

a landmass that originated as an island arc or a microcontinent that was later added onto a continent or other landmass

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13
Q

The nature of islands

A
  • well defined boundaries
  • relatively simple
  • often relatively small
  • often relatively isolated
  • are numerous ( # of oceanic islands in the pacific > 20 000)
  • Archipelagos - variations in size and degree of isolation amongst islands
  • Broadly defined - include true islands, mountaintops, ponds, lakes, caves, oases, forest patches, natural and anthropogenic islands
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14
Q

Ecological Scale

A

unique properties of island biotas - based on biotic and abiotic challenges and interactions

island impoverishment and species area relationships

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15
Q

Evolutionary Scale

A

Islands and speciation - endemic species, archipelago speciation

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16
Q

The Equilibrium Theory of Island Biogeography (ETIB)

A
  • role of rates of immigration and extinction in controlling species diversity
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17
Q

Unique properties of island biotas

A

Community composition - aspects of diversity

  • ecological roles
  • niche and breadth differentiation
  • population densities

Body size

Growth form

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18
Q

Island community composition

A

Mix of species on islands is often different than the mix of species on the mainland

Often fewer species on islands than comparable mainland areas

Often the relative density of species on islands is higher than comparable mainland areas

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19
Q

Harmonic (balanced) species composition

A

similar to mainland composition

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20
Q

Disharmonic (unbalanced) species composition

A

different than mainland composition

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21
Q

Harmonic biotas

A

expected is species are assembled randomly from mainland source pools

22
Q

Disharmonic biotas

A

expected if non-random processes are important

–> non random processes: differential ability amongst taxa to migrate and colonize, or to persist once established

23
Q

Disharmonic Island Communities

A

Non random processes - islands differ from the mainland and each other

WHY?
-taxa differ in dispersal abilities
-taxon specific biota differ in degree of disharmony
-flying taxa - disproportionatley common on islands
other taxa (fish, mammals, amphibians) - disproportionatley uncommon on islands

24
Q

Different Dispersal Abilities

–> active dispersal and examples

A

Active dispersal - flight, ability to cope with seawater

Active dispersers - bats, birds, insects

25
Q

Different Dispersal Abilities

–> passive dispersal and examples

A

Passive dispersal - high altitude winds, high velocity winds, ocean currents, hitch hiking on or in another organism (zoochory)

Passive dispersers - via spores (microbiota, fungi, ferns), via fruits and seeds (flowering plants), via egg masses (insects, some vertebrates)

26
Q

Island biota: ecological roles

A

many island species are generalists

  • resourse limitations (food)
  • lower demands - greater chance of establishing a persisting population
27
Q

Advantages of being a small bodied generalist

A

Food is limited on islands usually

  • small animals need less
  • generalist so they use many diff sources
  • small animals can maintain a higher max population
  • –> less susceptible to extenction

Often small islands have only one species of a particular animal or bird

28
Q

Species-Area Relationship

A

in general - the greater the area, the greater the number of species supported

for islands - the # of species is less than the number in comparable area of mainland - most islands suffer some degree of species impoverishment
- not linear, richness increases less rapidly for larger islands

29
Q

Islands: ‘Species Poor’ Biotas

A

Generally isolated islands have fewer species than mainland locations of comparable area

Smaller islands - greater rates of extinctions

30
Q

Island Biota: Higher Densities

A

Population densities can be higher than on any comparable mainland

  • niche breadth and density both increase
  • similar trends seen in birds on small islands and lizards on Gulf of Cali islands

WHY?

  • reduced congeneric competition
  • reduced competition with other unrelated but insectivorous taxa
  • release from their own predators (lack avian predators on many islands)
  • access to a greater variety and density of food resources (lots of insects)
31
Q

Density ‘overcompensation’ on small islands

A

this is common

  • large vertebrate (top predators) are usually absent
  • absence of congeners; absence of ther members of the feeding guild; net result, reduced competition
  • absence of other predators and/or parasites
  • presence of high densities of insects (food)
  • more finely adapted populations to local conditions
  • surrounding H2O prevents emigration from marginal habitats - increasing total local density
32
Q

Body Size: the ‘Island Rule’

A
  • graded trend, with and among taxonomic groups
  • tendency for small animals to become bigger, and big animals to become smaller
  • seems to apply for most mammals, some birds, snakes and turtles, perhaps deep sea marine species too
33
Q

Dwarfism

A
  • ‘normally’ big animals become smaller

Examples:

  • Wrangel Island (Northern Siberia) mammoths
  • Elephants of Sicily and Malta in Pleisocene - size was ~ 5% of mainland relatives
  • similar trends for deer, ground sloths, hippopotami, and other mammals - body size proportional to island area
34
Q

Gigantism

A
  • ‘normally’ small animals become bigger - a trend very often seen for herbivores and seed eaters (rodents, iguanas, tortoises)

Examples:

  • Closest living relatives of the Galapagos tortoises (~150 cm) are the chaco tortoise (max length ~23cm)
  • Giant house mice of gough island ~2X bigger than their ancestral size
  • Giant insects - weta of New Zealand
35
Q

Small animals - promotion of larger size (gigantism)

A
  • biased initial breeding stock ( successful colonists likely to be larger (immigrant selection))
  • in absence of predators, herbivores can feed more often and more rapidly - access to more food, they grow amongst themselves - intraspecific competition can favour bigger organisms
  • in the absence of other species of competitors (ecological release, reintroduced interspecific competition), island species can occupy wider niches - can lead to increased body sizes
36
Q

Large animals - promotion of smaller size (dwarfism)

A
  • few or no predators - little or no selective pressure for large size protection
  • more intense intraspecific competition for limited resources - advantage to smaller size and faster time to maturity and reproduction
  • limited resources potentially leads to increased specialization and perhaps smaller size
37
Q

Body size on islands - general conclusions

A
  • net energy to be gained per unit time is important
  • presence of a cogeneric species can be important (what niches are still available?)
  • presence of potential predators can be important
  • the total amount of resources available can be important
  • island species evolve more quickly than mainland species
  • there may be threshold sizes for body size change in mammals
  • for mammals, median body size actually decreases as land area increases
38
Q

Role of Isolation

A
  • Diamonds study of non- marine resident birds of Moluccan Islands and the Melanesian archipelago and farther
  • Only islands close to the source (New Guinea) have close to the expected number of bird species (near saturation)
  • The greater the distance from the source pool, the more depauperate the avifauna
39
Q

Role of Isolation - smaller spatial scale

A
  • As distance increases, non-volant mammal species richness decreases for the Saint Lawrence
40
Q

Temporal Isolation

A

In the Gulf of California, so-called land-bridge islands that have been isolated for longer periods of time have fewer species

41
Q

The ETIB: Background

A
  • islands are recipients of species from a source pool of species living on a mainland area
  • the number of species received by an island depends on:
  • -> island size (area), island distance from mainland (isolation), the source pool of species and their characteristics (richness, vagility)
42
Q

ETIB: Genera on Isands

A

fewer genera on isolated islands (distance matters)

fewer genera on small islands (size (area) matters)

small, isolated islands have the fewest genera of all (ex. Easter Island)

Birds on Pacific Islands
- # of genera positively correlated with island area

43
Q

ETIB: Why does distance matter?

A
  • longer distances to travel make it more difficult for immigrants to get to an island
  • –> more time and energy, might die before getting there, fewer individuals make it

Islands that are far away have lower rates in immigration than islands that are closer to source pools of species

44
Q

ETIB: Why does area (size) matter?

A

Bigger islands might have

  • greater variety of topography
  • greater variety of possible habitats
  • higher resource levels
  • potentially larger populations

Larger islands have lower rates of extinction, smaller islands have higher rates of extinction

more plant taxa, likely more animal taxa

45
Q

The ETIB: The processes

A

MacArthur and Wilson 1967

  • main parameters: distance (isolation) affects the rate of immigration, size (area) affects the rate of extinction
  • mechanism: balance b/w rates of extinction, and development of “most probable curves”
  • these rates control, at equilibrium, the number of species (S), and the rate at which species “turn over” (T)
46
Q

Effect of Distance (Isolation)

A
  • Two equal sized islands that differ in distance from the source pool have the same extinction rates, but different immigration (colonization rates)
47
Q

Effect of Island Area

A
  • Two different sized experience the same rate of immigration (colonization), but extinction rates are greater on the small island
48
Q

ETIB: Assumptions

A
  • new species immigrate and old species die out at random
  • immigration and extinction are independent processes
  • the source of colonists in the mainland
  • area and isolation alone are sufficient to predict immigration and extinction rates
  • speciation occurring on islands is not included in predicting species richness, number of species at equilibrium
  • disturbances in ecological or geological time are not considered
49
Q

ETIB: Overall Predictions

A
  1. # of species on an island stabilized at a constant value
  2. The stabilized value is dynamic - continual turnover of species due to immigrations and extinctions
  3. If deg. of isolation is the same - large islands will support more species than small islands, but small islands will return to equilibrium more quickly
  4. If island size is the same- more resident species on nearby island and nearby island will return to equilibrium more quickly
50
Q

What does the ETIB not do?

A
  • does not predict species identity (it predicts species richness)
  • does not predict the timing of changes (predicts turnover)
  • does not predict anything about relative species abundances
  • does not predict anything about speciation in the past, present, or future

Biogeo (1 decks)

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