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Lecture 28

NATS 1940 Lecture Notes - Lecture 28: Allopatric Speciation, Dna Barcoding, Species Richness

Natural Science
Course Code
NATS 1940
Mark Vicari

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Lect 28:
* Diversity on Islands, How many species? & DNA Barcoding:
Diversity on Islands:
Isolation of island populations → allows for allopatric speciation to take
Endemic species:
Species unique to a specific geographic location
Initially new species are endemic to that island (not found elsewhere)
Later may spread to other islands or inland
Which is a cluster of islands or chain of islands
Lead to many opportunities for isolation which results in high
speciation rates
Ie: Hawaiin Islands:
The hawaiin islands contain 90% of plant species that are
Along with other species
High diversity is due to variations in climate, vegetation
patches by lava flow
Older islands (west) generally contain species ancestral to
younger islands (east)
Basically the Hawaiin islands are over a hotspot (lava/
core melting the crust of earth forming volcanoes) and
as the plate moves east it forms new islands therefore
older islands created before move west and form a chain
of islands west to east
Most islands species are not endemic (arrive by dispersal)
More isolated islands → lower colonization rate
But also more endemic species
Less gene flow
Faster allopatric speciation
species richness tends to decrease with higher isolation
Increase in endemic species but a decrease in species

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Expansion of Niches:
In absence of competitors, island species may occupy new habitats
Ie. ants
In florida mainland:
Nests only in shaded ground
In florida keys:
Nests in shady grounds but also in open soil and
tree trunks
Not evolutionary change but simply the release from
Evolutionary Diversification:
Adaptive Radiation:
Adapt into new and unoccupied niches
One species diversifying to form new species that fill different
and open niches
Ie: Sarcopygme
Found on Samoa island
Mostly shrubs but have evolved on the island as trees
are rare on islands due to their large , poorly dispersed
seeds therefore the Sarcopygme evolved into trees in the
absence of competition
Loss of Flight:
Often occurs once a flying species has become established
In insects
Flight may be a disadvantage especially on small islands
May risk being blown out
In plants:
Loss of winged/ tufted seeds
In birds:
Loss of wings in birds
May reflect a lack of predators
Or a possible disadvantage presented having wings
Ie: Maybe the energy and nutrients were better
used in producing eggs or something else more
important to fitness
Change of Size:
On islands
Small species tend to become larger:
Often due to release from predation and the pressure of
natural selection acting on it
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