Transcript Speciation and Extinction

Systematics
• Study of pattern and processes associated
with biological diversity and diversification
• Taxonomy – study of classification
(hierarchy, naming  Diversity)
• Phylogenetics – study of evolutionary
relationships between species and groups
(Diversification)
Species Concept
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Biological species concept – definition
All species concepts have limitations
Classification is a human construct
Importance of defining a species
Phylogenetics
• Homologies
Phylogenetics
• Convergence
Phylogenetics
• Apomorphy – derived
trait
• Pleisomorphy –
primitive trait
Subspecies
Populations – coat color of subspecies match local substrate
Evolution
• Macroevolution – lineages of species and
major groups, changes in diversity
• Microevolution – changes in species, short
and longer term; contemporary species
• Not segregated; difference in scale
Macroevolution
• Evolution does not proceed at a uniform
rate
• Bradytelic – lineages changing at slower
rates than typical
• Tachytelitic – faster rates than typical
• Horotelic - typical
Punctuated Equilibrium
• Proposed abrupt changes in lineages
following long periods of stasis
• Mass extinctions  adaptive radiation
• Does not contradict natural selection; still a
key process in punctuated equilibrium
• Gradualism also occurs
Gradualism
Macroevolution
• Rapid Radiation not
always with mass
extinctions
• Cambrian Explosion
• Mass extinctions
may not be random
• Species selection
(large sp. end
Cretacrous
Mechanisms of Evolution
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Mutation
Genetic drift
Gene flow
Natural selection
Adaptation and Range Expansion
• Range of a species includes range of
populations
• Populations on edge of range may adapt to a
limiting condition
• Some species may not have capacity to
adapt morphologically, physiologically, or
behaviorally peripheral conditions
Adaptation and Gene Flow
• Gene flow changes allele frequencies of
populations
• Can, however, homogenize gene pool
through exchanges between populations
• Restricts further adaptation to local
conditions
• Other limitations to adaptation limit range
expansion (not all species have wide ranges)
• Distribution of karyotypes of Palestine
mole rat (Nannospalax ehrenbergei)
• Lack of overlap  reduced gene flow
Geographic Variation
• Geographic isolation facilitates genetic drift
and natural selection
• Impedes gene flow
• Genetic drift – isolation of small populations
• Founder effect
• Divergence of monarch flycatcher
• Founder effect – colonizers of islands
created gene pool for each
Allopatric Speciation
• Speciation resulting from geographic
isolation
• Broader definition applying environmental
and physical barriers
• Dispersal barriers in heterogeneous
environment
• Geographic isolation after dispersing to
another habitat (e.g., island to island)
Allopatric Speciation: Vicariance
Endemic Mad.
All in Family Ranidae
Sympatric Speciation and Adaptive Radiation
Extinction
• Changing of the guard (dominance in given
niches)
• Cephalopod molluscs  teleost fishes
• Dinosaurs & reptiles  birds and mammals
• Species are eliminated or supplanted in
their lineages
Extinction
• Probability of extinction independent of
evolutionary age
• Is related to taxonomic and ecological status
• Small, herbivorous mammals lower
extinction rates than large carnivores
• Same true for marine invertebrates
• Ties back to point about more niches for
small organisms?
Extinction of Species
• Primary causal mechanisms for extinction
• Reduction of population sizes
• Habitat changes
What pushes numbers of a species down to the
point where it is pushed to extinction?
Fossil Record and Mass Extinctions
• Many events, many hypotheses
• Pleistocene – megafauna of N. and S. Amer.
8,000 – 15,000 yr ago
• Once thought to be climate change from
recession of glaciers
• More evidence that human colonization was
a major contributor
Fossil Record and Mass Extinctions
• Permian-Triassic 250 mya
• 96% of marine species lost
• Causal Agent?
– Climate change but how
– Glaciation
– Global warming
– Massive volcanic activity
– Continental drift
> 100 Species
4 - 5 Species
Seabed in P-T before and after mass extinction
Species Selection
• What leads to species surviving and
radiating after extinctions?
• Appear to be key traits
• Remaining species in range also a factor
• Expansion of mammals after K-T extinction (65
mya)
• Filled niches left behind by dinosaurs and
reptiles pushed to extinction
Placental Mammals
• Found globally in fossil
record
• Few extant species in N. &
S. America
• Australian marsupials
• Why?
• Adaptive radiation in
absence of dominant
reptiles
• Later natural and human
intro of placentals
Dispersal Advantage
Replacement