Extinction: Bad Genes or Bad Luck?

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Extinction Bad Genes or Bad Luck?
Defined- the complete death of a taxon
Not to be confused with gradual evolutionary
change that leads to the creation of a new species
Which is termed as Anagenesis
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Possible Fates Over Time for Species A
Species A
Species D
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Possible Fates Over Time for Species A
Extinction by demographic failure
Extinction by Genetic Swamping
Species X
Species X
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Extinction as a Natural Process
Life as we define it has existed on earth for 4
billion years
Possibly as many as 4 million species on earth
today
Estimated that 50 billion species have lived on
earth
Thus, less than 1 in 1,000 species that have
lived on earth are alive today!
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Characteristics of Extinction-Prone Species
1. Low reproduction rate
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2. Species with specialized feeding habits
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Koalas- eat only leaves from certain species of
eucalyptus tree
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3. Species that feed at high trophic levels,
such as, Bengal Tiger or
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5. Limited or specialized nesting or breeding
area, such as Kirtlands Warbler which breed only
in burned over jack-pine forest stands in
Michingan, Minnesota and Canada
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6. Found only in one place or region, such as
the elephant seal from the Pacific Coast or...
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Unique island forms such as the Hawaiian
Honey-creepers including the O-O complex
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7. Species with fixed migratory patterns,
including Whooping Cranes
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Gray Whale migration route
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8. Species that are purported to prey on
livestock or people
Coyote
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American Alligator
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9. Unique behavioral patterns, such as Key Deer
and .
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Social Facilitation in Passenger Pigeons
Remember- the Fraser Darling Effect
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Population Size
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10. Species with poor dispersal or colonizing
potential
Such as flightless birds, including the Dodo
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Or island forms such the Aye-Aye
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11. Species such as frugivores and nectivores
that exploit unreliable resources
Complex of Hawaiian Honeycreepers
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12. Species that cannot tolerate habitat
disturbance such as forest interior bird species
Kentucky Warbler of the Southeastern North
America deciduous forests
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Multiple Factors
Specialized feeding habits
Low reproductive potential
Unique island form
Poor dispersal potential
Cant tolerate disturbance
Found in only one place or region
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Deterministic Processes and Decline to Extinction
Stresses that affect populations in direct,
detrimental ways by
Increasing mortality
And/or decreasing reproduction
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Deterministic Processes and Decline to Extinction
1. Direct killing
Great Auk- killed for meat and oil
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2. Introduced predators such as rats, cats and
mongoose
Hooded Warbler- ground nesting songbird in the
eastern United States
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3. Exotic predators introduced accidently
12/14 bird species 2/3 bat species 6 lizard
species
Native of southeast Asia, Philippines, Indonesia
Arrived on Guam accidently, probably in a
shipment of fruit
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4. Introduced species out-competing native
species for resources, thus driving them to
extinction.
Galapagos Rice Rat
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5. Introduced species as vectors for disease
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6. Genetic swamping
Mallard- drake
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Mallard Hen
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Mallard Group
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Mallard
Mexican Duck
Black Duck
Mottled Duck
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7. Habitat Disruption
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Historic Whooping Crane Migratory Stop-over site
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North American Farming Practices
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Brown-headed Cowbird
A brood parasite formerly confined to the Great
Plains in association with Buffalo Herds
Female
Male
Brood Parasitism laying eggs in the nest of
another species
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Female Cowbird laying an egg in a vireo nest
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Habitat Fragmentation
The breaking up of contiguous tracts of habitat
into smaller, not-connected patches
Accomplished in a variety of ways including
Results in creation of patches that are below the
minimum area needed for survival and reproduction
Concept of Species Area Curves- the illusive
figure 5.8 page 49