Problems of Island Existence: Conditions on the Hawaiian Archipelago and Other Oceanic Islands

1
Problems of Island Existence Conditions on the
Hawaiian Archipelago and Other Oceanic Islands

• Inspected by Andrew Bishop 8

2
Oceanic island chains (archipelagos)
?Did not arise from the mainland
?Evolution occurs more rapidly than frequency
of new immigration events

• ?Some of the most isolated environments on earth

?Pre-human colonizations by terrestrial
organisms through airborne means
3
Colonization event
?
Movement from a core population to a satellite
population
Initially, this is bad for genetic variability
of immigrant species
Why?
4
A minimum viable population is the minimum
number of individuals needed to maintain a
population for the projected future, despite
stochastic events.
The effective population size (Ne) is the
amount of individuals that are successfully
breeding.
3 big factors cause decline in Ne

• unequal sex ratio (affects
• high dieocy flora esp.)

2) variation in reproductive output
3) population bottlenecks
5
A bottleneck is an event in which the
population decreases far enough that rare
alleles are lost
The founder effect is when individuals of a
population immigrate to colonize another area,
and form a new population.
3 factors count against small populations
1) loss of genetic variability
2) demographic stochasticity
3) environmental stochasticity
6
Minimum dynamic area is the minimum habitation
area required to maintain the minimum viable
population size.
7
Problems of oceanic island existence (in
particular Hawaiian archipelago)
Far from any and all continents, and geographic
distance diminishes gene flow
After colonization event, isolated satellite
population is small
Possible habitat area is very limited compared
to mainland
8
Advantages of oceanic island existence
Isolation theoretically quickens speciation
rates, since pressures implicated with a new
environment facilitates selection
No competition early on, many niches able to be
filled
Hawaiian islands are particularly large for
oceanic islands
9
Response of oceanic island biota to these
conditions
1) Good dispersal methods needed for colonization
(lightweight seeds or spores, flying insects or
birds)
2) Endemic species lose these (loss of wigs, seed
gigantism)
? Hawaii has many different microhabitats weak
seed dispersal keeps primary producers in the
habitat theyve adapted to
? Insects and birds lose wings, predators not
abound
3) High speciation rates prevent inbreeding
depression
? It is theorized that archipelagos act as
speciation mechanisms

• Geographical distances balance inter-island
  immigration (not too
• far to completely exclude immigrations, not too
  often either,
• letting speciation occur between immigration
  events)

4) High rate of dioecy in plants, and often
gigantism and nanism
10
Love it or leave it, oceanic island conditions
include
A climate less prone to temperature extremes
more humid and windy than continent
Deficiency in mammals (except bats), amphibian,
and ancestrally freshwater fish
Many ferns and other pteridophytes, very few
conifers
11
References

• Carlquist, Sherwin. Hawaii A Natural History.
  The Natural History
• Press. Garden City, New York. 1970

2) Primack, Richard B. A Primer of Conservation
Biology. Sinauer Associates, Inc. Sunderland,
Massachusetts. 1995
3) Whittaker, Robert J. Island Biogeography
Ecology, Evolution, and Conservation. Oxford
University Press. Oxford, New York. 1998
4) Williamson, Mark. Island Populations. Oxford
University Press. Oxford, New York. 1981
5) Hawaii Forest and Trail. May 30, 2003.
http//www.hawaii-forest.com/evolution.html
6) Hawaiian Native Plant Genera. May 30, 2003.
http//www.hawaii-forest.com/evolution.html