Biogeography

Biogeography

• is the study of species composition and diversity over geographic regions

• latitudinal variation

how does species diversity varies with latitude?

• higher diversity at low latitudes for most taxa

• except sea birds, seasonally high marine productivity in higher latitudes

why are tropics more diverse?

• global diversity is controlled by speciation and extinction

  • species diversification = speciation - extinction rate (hard to test)

  • 3 hypothesis:

    • species diversification rate is higher in the tropics

    • diversification rates are similar, but evolutionary time is greater in the tropics

    • higher productivity results in more abundant resources in the tropic that can support more species (carrying capacity)

h1 tropical biodiversity: species diversifiction rate

• the tropics have the most land area on earh, and temperatures are very stable

• large thermally similar areas should have low extinction rates, population sizes and geopgraphic ranges would be larger

• speciation by geographic isolation would be more likely

• first graph on image

h2 tropical biodiversity: species diversification time

• the tropics have been climatically stable for more time and therefor species had more time to evolve

• 65 mya the entire earth was warm, tropical biome extended all the way up in to europe and the northern us

• temperate and polar regions have undergone severe climatic changes, last glacial maximum 20 ka disrupting species diversification

h3: productivity

• terrestrial productivity is highest in tropics

• high productivity promotes large population sizes because carrying capacity is larger leading to lower extinction rates

• productivity could explain the reverse pattern in sea birds but, some really productive habitats have low diversity

what will happen to the latitudinal diversity gradient with global warming?

• it will become shallower, move down, or be non linear

biogeographic region

• biotas of the continents reflect evolutionary isolation

• portion of the earth containing a distinct biota that differs from the biotas of other regions in species composition and diversity

• wallace’s line: in SE asa an invisible line that seperates distinct fauna of asia and australia

regional species pool (gamma diversity)

• all of the species within a geographic region that have the potential to colonize and inhabit a particular local area

  • includes multiple local sites

• island biogeography example

regional biodiversity: island biogeography

macarthur and wilson’s equilibrium theory of island biogeography (1967)

the number of species on an sland depends on a balance between immigration and extinction

• dynamic equilibrium

• island size controls extintion

  • small islands have more extinction due to small population sizes

• distance from mainland controls immigration

for the island biogeography, how can it shift based on size and proximity?

• dynamic equilibrium

• island size controls extintion

  • small islands have more extinction due to small population sizes

• distance from mainland controls immigration

• near and large will have the most species, far and small the least

• the point where the two rates cross is the number of species you will find

how do we test the island biogeography

• bird richness on krakatau predicted s = 30

• mangrove islands in florida

  • spayed insecticied to remove all insects and spiders, after a year similar numbers were found and the islands closest to a colonizer community had the most species

• can be applied to mainland, matrix doesn’t have to be water

landscape scale (beta diversity)

• physical geography of a region

• landscape connectivity shapes immigration and emigration

• beta diversity is the change in species diversity and composition (turnover) from one plot to another

• if there is high beta diversity = high difference between sites

local scale (alpha diversity)

• abiotic and biotic characteristics

• alpha diversity local at a plot

• just the unique species at a plot

if there is a regional species pool of 11 species, you sruvey two plots in a preserve, what would the plots look like if there is high alpha diversity but low beta diversity?

they would look similar, a low beta diversity means most of the sits are similar

if there is a regional species pool of 11 species, you survey two plots in a preserve, what plots look like if there is low alpha diversity but high beta diversity?

• few total species btween the two plots and minimum species overlap

sorenson’s dissimilarity

sorrenson’s dissimilarity = 1- 2*SharedSpecies/ (S1+S2)