Module 12: Biogeography

biogeography is the study of

spatial (geographic) patterns of biodiversity, and is concerned with how and why organisms came to possess their geographic distributions. biogeography is focused on the geographic distributions of organisms (including species, and higher level taxa all the way from genus to phylum) in both the present and past

zoogeography

animal biogeography

phytogeography

plant biogeography

historical biogeography

the reconstruction of the origin, dispersal and extinction of taxa, as well as entire biotas

phylogeography

the branch of biogeography that considers the principles and processes that control the geographic distributions of genetic lineages, particularly within species, and among very closely related species

dispersal

the movement of organisms away from their point of origin

vicariance

the splitting of floras and faunas (or populations) as a result of the formation of a physical barrier

endemic

found only in one specific geographic location

biogeographic province

a region with a unique set of plant and animal species, often including endemic species

why does fish diversity increase from north to south in north america?

the north was heavily glaciated during the Pleistocene, destroying habitats, southern areas acted as refuges

what were teh 5 major glacial refuges in North America during the Wisconsin glaciation

Beringian, Pacific, Missourian, Mississippi, Atlantic

What is a glacial refuge (refugium)

an unglaciated area where species survived during glaciations

what evolutionary process occurred when populations were isolated in different refuges

allopatric divergence

what are pro-glacial lakes and why were they important

large lakes formed from melting glaciers; they created dispersal corridors for recolonization

how is phylogeography usually conducted

by sequencing DNA (often mitochondrial) from individuals across a species’ range

in the arctic char example: 3 refuges (beringian, atlantic, N.atalantic) which dispersed most widely

beringian refuge

in the lake trout example: 5 refuges (N. Beringian, S. BEringian, Missouri, Mississippi, Atlantic) what prevented atlantic refuge fish from moving far west

Niagara falls

What major event shaped similar genetic patterns in many species

Plesitocene glaciations (a vicariance event)

phylogeography shoes which

refuge species came from and how they recolonized

different species often show parallel genetic patterns

due to the same vicariance events

what is the latitudinal gradient in species diversity

species diversity increases from the poles to the equator

who first recognize the latitudinal diversity gradient

Charles Darwin and Alfred Wallace

example of tree species diversity along the gradient

central american rainforest: 40-100 species/ha; Eastern North America 10-30 Boreal forest 1-5

what trend is seen in species endemism from north to south

endemism increases toward the south

what does Rapoport’s Rule state?

species ranges increases with latitude, northern species tend to have larger geographic ranges

according to rapoport’s rule, which have better dispersal abilities - northern or southern species

norhtern species

name the three main factors contributing to the latitudinal diversity gradient

historical (e.g glaciations) ecological (climate, solar energy, productivity), evolutionary (speciation/extinction rates)

true or false: speciation rates are always higher in tropical regions

false - some taxa have higher speciation rates in northern latitudes

Law of geminate species (jordan’s law)

closely related species (geminate species) are often found on opposite sides of a geographic barrier, with each species occupying a similar ecological niche in its respective area

“mechanism” of jordan’s law

1. a once-continous population becomes split by a barrier

2. geographic isolation → allopatric divergence through mutation, selection, and drift

3. result: two “twin” species with strong similarities but distinct distributions

jordan’s law illustrates how

vicariance events create parallel speciation patterns across a barrier

the formation of the isthmus of panama had two very different impacts on terrestrial and marine ecosystems

1. terrestrial: dispersal (allowed land animals and plants to cross between continents”

2. marine: vicariance (geographic separation leading to divergence)

molecular clock

a method that estimates the time since two species diverged by measuring the number of genetic differences between them

why the isthmus is useful for calibration

we know when the barrier formed (~ 3 Ma), so it acts as a natural timestamp for calibrating mutation rates in marine species that were split by it

snapping shrimp as an example

before the isthmus formed: shrimp populations were continuous, interbreeding freely across teh central american seaway

after: populations were split into pacific and atlantic/caribbean side, no gene flow → allopatric divergence occured

each atlantic species has a “twin” pacific species (geminate species pair)

they look morphologically similar but are genetically distinct

why is the formation fo the ismuth of panama important

It connected North and South America, which allowed species that had evolved separately until then to migrate and start interacting with each other., This allowed for the Great American interchange, and the migration of species from North America to South America, and vice-versa

the formation of the Isthmus of Panama occurred

3 million years ago

we know that geminate species were separated when the isthmus of panama was formed, this known emergence time allows us to calibrate

moleular clocks. this means that we can calculate the rate of molecular evolution for those species