Chapter 9 con’t

March 14th

Founder Principle

• Founder principle – populations founded by a very small number of individuals generally contain a small subset of the total genetic variability of the main population and are prone to allopatric speciation

• Genetic bottleneck – decreased genetic diversity resulting from decreased population size

• Peripatric speciation – when peripheral populations become geographically isolated from the main population and undergoes speciation and genetic divergence

Tanysiptera galatea

Tanysiptera sylvia

Tanysiptera carolinea

• Natural Selection favors traits that increase survival and reproduction

• Flightless birds, insects, and seeds

• Continental relatives can fly

Guam rail Hawaiian Goose “nene”

Vicariance Event• Populations split by geographic barrier

initiating allopatric speciation

• Boreal biome split by Laurentide Ice Complex

• Species differentiation slower in larger populations

Adaptive Radiation

• Adaptive radiation – the development of many species from a single species – new species fill all available niches in the colonized region

• Example: Hawaiian honeycreepers have variety of beaks to take advantage of different foods

Species of Hawaiian honeycreepers descended from a common ancestor, some of which are shown here, have evolved many different bill shapes and food sources. (Paintings copyright H. Douglas Pratt, The Hawaiian Honeycreepers: Drepanidinae. Oxford: Oxford University Press, 2003. Diagram adapted from T.J. Givnish and K.J. Sytsma, eds., Molecular Evolution and Adaptive Radiation. Cambridge: Cambridge University Press, 1997.)

Adaptive radiation in cichlid fish from Lake Malawi in East Africa

Convergent Evolution

Evolutionary convergence; (From Top to Bottom) An ichthyosaur Ophthalmosaurus icenicus, a Porpoise, and a Spiny Dogfish (Squalus acanthias)

Parallel Evolution

Extinction

• Extinction is the loss of all individuals in the population of a given species, genus, family, or order– Local extinctions:

American buffalo (Bison bison)

• Global extinction – loss of species or higher taxonomic order over its entire range

• Abundant in North America, Europe, and Asia before 12,000ya

• Extinction caused by combination of over hunting (Pleistocene overkill hypothesis) and climate change

• Trophic cascades – when the loss of a prey species causes further ecosystem disruptions because of the loss of food for higher predators

• Phyletic extinction – pseudoextinction – species evolve into new species with many of its genes persisting in descendant species

• Example: Hyracotherium to Equus

Mass Extinctions

• Late Devonian (360 mya)• Permian (250 mya)

– 50-96% of land and marine species becoming extinct

– Large extinction of insects– Caused by (?) climate cooling or poisoned oceans

• Late Triassic (200 mya)• Late Cretaceous (65 mya)

– Extinction of dinosaurs– Caused by meteor

• Late Tertiary (2 mya)– Climate cooling

Dinosaur Extinction• KT Boundary – geologic boundary between the

Cretaceous and Tertiary 65 mya

• A large amount of iridium at this boundary indicated large meteor or comet slamming into Earth

• Large amounts of shock quartz and evidence of large fires found at this boundary

• The collision of meteor and Earth caused fires, tsunamis, followed by nuclear winter, and then extreme greenhouse effect

• Red Queen Hypothesis – If a species cannot evolve fast enough to keep up with competing species, it will become extinct

• Could lead to an evolutionary trap – overspecializing in an isolated area

• Or blind alleys – when genetic diversity is lost during evolution, making environmental changes more problematic

• Those prone to extinction:– Larger animals– Species with complex behavioral,

morphological, or physiological adaptations– Predators at the top of food chain– Specialists species– Species with small population size– Species with low birth rates, or long gestation

periods– Species with small geographic ranges– Poor dispersal capabilities