systematics study of pattern and processes associated with biological diversity and diversification...
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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
• 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
• 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
All in Family Ranidae
Endemic Mad.
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
Seabed in P-T before and after mass extinction
> 100 Species 4 - 5 Species
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