Systematics Study of pattern and processes associated with biological diversity and diversification Taxonomy – study of classification (hierarchy, naming.

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