Natural Selection, Speciation, and the history of earth (L5)

Exam 1 Lecture 5

Directional Selection

• favors an extreme end of a phenotypic distribution that has greater reproductive success

Ex: white vs brown moths in a forest

Stabilizing selection

• favors individuals with intermediate phenotypes

Ex: Egg clutch sizes

Balancing selection

• maintains genetic diversity in a population

• 2 or more alleles are kept in balance

• includes heterozygote advantage (sickle cells), and frequency-dependent selection

frequency-dependent selection

• positive selection - common phenotypes have the advantage (warning colors)

• negative selection - rare phenotypes have the advantage

Disruptive selection

• favors the survival of both extremes of a phenotype

• Ex: metal-tolerant grasses and non-metal-tolerant grasses, no in between

Biological species concept

• groups of populations that can interbreed and are reproductively isolated from other populations

Phylogenetic species concept

• species are distinguishably different via morphology

Evolutionary species concept

• A species is distinct if it has its own evolutionary tendencies / historical fate

• Formation in the fossil record + phylogenetic trees

Ecological species concept

• species separate based on different ecological niches + habitats

Paleozoic Era

• Cambrian → Ordovician → Silurian → Devonian → Carboniferous → Permian (Cats Only Sing During Choir Practice)

Cambrian Period

• Cambrian explosion = marine invertebrates

• ozone layer formation

Ordovician period

• First terrestrial life (plants+fungi)

• first chordates

• At the end: Ice age and mass extinction

Silurian Period

• First jawed fish

• Arthropods + vascular plants became terrestrial

• 2 large continents

Devonian Period

• fish diversification (first bony fish)

• co2 went down, o2 went up

• amphibians and insects appear

• at the end: Ice age + mass extinction

Carboniferous Period

• Reptiles arise

• insects explode

• planet cooled

• extensive forests give rise to coal beds

Permian Period

• pangea formation

• extinction of amphibians + marine invertebrates

• planet heated up

• seed plants arose

Mesozoic Era

• Triassic → Jurassic → Cretaceous

• Pangea splits into Gondwana and Laurasia

Triassic Period

• Pangea drifted apart / sea levels rose

• dinosaurs and mammals appear

• at the end: mass extinction

Jurassic Period

• Dinosaurs dominate

• birds appear

• winged insects evolve with flowering plants

Cretaceous Period

• Angiosperms begin to dominate over gymnosperms

• dinosaurs go extinct (RIP)

Cenozoic Era

• Paleogene → Neogene → Quaternary

• current

Paleogene period

• Continents move to their current positions

• diversification of mammals and birds (due to dinosaur extinction)

Neogene Period

• More seasonal climate

• Atlantic/Pacific separate, Gulf Stream develops

• mammals adapt/migrate

• at the end: ice age

Quaternary Period

• Repeated glaciation events

• Homo evolution

Biogeographical Realms

• Nearctic

• Palearctic

• Neotropical

• Oriental

• Australian

• Ethiopian

• separated by major barriers like oceans or large deserts

Red Queen Hypothesis

• species must continually evolve just to stay still/ avoid extinction

Gradualism

• species evolve gradually/ over time

Punctuated equilibrium

• species evolve sporadically

Extinctions

• Ordovician, Devonian, Permian, Triassic, Cretaceous

• The Permian had the largest extinction

• The Cretaceous had a single large mass extinction event (meteor)