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Readings
• Readings on web page.
– BSCI: Chapter 2.
– CONS: Chapter 3.
• Anyone need a book?
Biological Species Concept
• “Groups of actually or potentially
interbreeding populations which are
reproductively isolated from other such
groups.” – Ernst Mayr, 1963
Conservation Implications?
• Complete reproductive isolation . . . would
not be satisfied even by some recognized
species that are known to sustain a low
frequency of interbreeding with related
species.
– Statement by the FWS and NMFS regarding
interpretation of DPS’s in response to public
comment.
http://endangered.fws.gov/policy/pol005.html
Mechanisms Promoting
Species Identity
• Biological
– Reproductive Isolation
• Cohesion
– Reproductive Isolation
– Natural Selection
Morphological Species Concept
Hedgehog Cactus
Phylogenetic Species Concept
mammary glands
live bearing
placenta
Non Mammalian
Vertebrates
Egg Laying
Mammals
Marsupials
Placental
Mammals
Review: Species Concept
• Why is a species a species?
– Biological: Reproductive Isolation
– Cohesion: Reproductive Isolation + Natural
Selection
• Is a species a species?
– Morphological: Practical Species Identification
– Phylogenetic: Evolutionary History
Species Concepts Applied
A. R. Templeton, in Speciation and Its Consequences D. Otte, J. A. Endler, Eds. (Sinauer Associates, Sunderland, MA, 1989) pp. 3-27.
Phylogenetic Methods: The Role
of Molecular Data
• Hybrid Species
• Genetic Management
• Evolutionary Significant Units
Evolutionary Significant Units
• A set of populations that is morphologically
and genetically distinct from other similar
populations.
• A set of populations with a distinct
evolutionary history.
DPS’s
• “Species” includes . . . any distinct population
segment of any species of vertebrate . . .”
• Discreteness
– “It is markedly separated from other populations . . .
Quantitative measures of genetic or morphological
discontinuity may provide evidence of this separation.”
• Significance
– “The discrete population segment differs markedly
from other populations of the species in its genetic
characteristics.”
http://endangered.fws.gov/policy/pol005.html
Extinction
Causes of Extinction
• Deterministic factors
(stacked deck)
– Realized growth rate is
negative
– Deaths > Births
• Stochastic factors (bad
luck)
– Intrinsic
• genetic stochasticity
• demographic stochasticity
– Extrinsic
• environmental variation
(EV)
• catastrophe
change in environment
K
Deterministic decline
to extinction
ln(N)
time
Population fluctuates
due to demographic and
genetic stochasticity
K
ln(N)
time
K
ln(N)
catastrophes
time
Population fluctuation
due to environmental
variation
Catastrophe
Severe and rare environmental variation
(Remember for Vortex)
Environmental Change and
Natural Selection
• Environmental change can result in negative
growth rates.
• Species will go extinct when unable to
adapt to such environmental change.
• Genetic diversity may buffer populations to
environmental change.
Deterministic Threats
• Change in physical environment
– climate change
– habitat destruction
– pollution
• Change in biotic environment
– Competition
– Predation (including disease and human hunting)
– Mutualism
Causes of Extinction
(Genetic Swamping)
Species / Population A
Extinction by genetic
swamping
Hybridization
Species B’
Species / Population B
Time
Environmental Variation
4000
Number of flower heads
3500
3000
2500
2000
1500
1000
500
0
1974 1977 1980 1983 1986 1989 1992 1995 1998 2001
How might climate change
affect this sunflower?