Biogeography

Biogeography

the study of geographic distributions of organisms

endemic

restricted to a particular geographic region

• bromeliads are restricted to New World

• plethodod salamanders in NA

• platypus to AUS

Narrow endemic

restricted to a small geographic region

• one flower in just Kauai ie.

Cosmopolitan

found worldwide (in an appropriate habitat)

• applies to many higher taxa (angiosperms)

Biogeographic realms (wallace)

major geographic regions of the Earth that have characteristic animal or plant taxa

Wallace’s line

sharp break in animal species among islands between eastern Asia and Australia despite proximity

• continental drift

  • two geologic plates that came together recently

Certain species or higher taxa may be restricted to a specific biogeographic realm

i.e. neotropical realm with armadillos, armored catfish

Biogeographic realm can be further divided into

regions of endemism (provinces) with unique flora or fauna

Disjunct distributions

geographic distribution that has unoccupied gaps separating regions that are occupied

Higher taxa typically have different but similar species in

disjunct regions

Boas are in South America and the South Pacific islands, and nowhere else, which is an example of

disjunct distributions

What are the three main historical processes that affect distributions?

• dispersal

• vicariance

• extinction

European starlings and cattle egrets are examples of species that have expanded their range via

dispersal; In a short amount of time a species can dramatically expand their range

Vicariance

separation of populations by barriers arising from changes in geology, climate or habitat

The Isthmus of Panama is an example of _____ ; as it split the marine organisms into the Caribbean and Pacific populations

vicariance

The modern horse is an example of how ____ can explain biogeography

extinction

• horses arose in NA, went extinct and later reintroduced

Dispersal, vicariance, and extinction need not be

mutually exclusive

Saxifruga cernua (a herby plant) is an example of

Dispersal, vicariance, and extinction

• glaciers split populations (V)

• dispersal (recolonized formerly glaciate regions)

• extinction (cold adapted populations in south went extinct with warming, remained in mountainous regions)

relict populations remain in high areas

progression rule

most basal lineages on Kauai, and youngest on Big Island

• makes phylogeny predictive

phylogeography

study of processes governing the geographic distributions of genealogical lineages

In phylogeography, we use ____ to draw inferences about historical processes

gene trees

• can be applied within species and across

Pleistocene population shifts

glacial cycles changed climate and made large areas of north temperate zone uninhabitable for most species

• also impacted tropical regions

Glacial refugia

locations where populations of a given species survived during the glacial maximum

Many northern temperate taxa show evidence of recent or ongoing ____ to the north

range expansions

species richness

number of species

Rarefaction

accounting for variation in sample size when calculating species richness

• can compare disimilar sample sizes

diversification

increase in the number of taxa in a clade

time-and-area hypothesis

most lineages have been diversifying over longer time periods and over larger areas in the tropics

• frogs more diverse in tropical than temperate

Time calibrated phylogenetic trees (chronograms) can be used to estimate

diversification rates

Lineage-through time plots

count up lineages existing over different times

• log number of taxa over time

  • slop of the line provides the estimate of r (per capita diversification rate) `

In lineage through timeplots, the graph

typically curves upward near the present (increasing diversity rapidly)

The slope in the recent past represents the speciation rate (S)

new things that havent had time to go extinct yet

Why are some clades so much more species rich than others?

Older clades may have more species

• i.e. beetles

Negative diversity dependent diversification

the diversification rate is dependent on how much diversity exists at that time

• there is a ceiling to it (carrying capacity)

• no relationship between species richness and clade age

Diversification rates slow towards the present

S = 0.56; ancestor 5 mya from CA

vast number of nodes near the present, not a lot in the past - high diversification rate over a small period of time

Clades that evolved herbivory diversified faster than those feeding on

animal, fungus or detritus