Biogeography

how many major extinction events?

5

dominance of humans caused background extinction rates to increase

humans might cause the 6th mass extinction

earth’s species richness is impossible to calculate

buffon’s law

Despite having similar climate different regions of the globe frequently have distinct biotas

America Regions

• Nearctic Region

• Neotropical Region

• Andean Region

Consider ecological aspects of distribution and then historical distribution processes

Alpha diversity

Local diversity, number of species found in a specific homogenous site

Beta diversity

Species turnover, change in species competition over relatively short distances

Gamma diversity

Regional diversity, number of species in a broad geographic region

Species accumulation curve

Show how the total number of species observed in a particular area increases with sampling effort

What determines local species diversity

• The number of species is determined by the number of species in the regional species pool, gamma diversity. Each time a space opens, it may be settled by any colonist in the regional space

• The number of species is determined by local species interactions. Competition for space and other resources drive alpha diversity by determining which species can survive at any given site and whether or not a new species cna successfully colonize it

Specie turnover

• Beta diversity

• Alpha diversity of birds is mostly in the tropics

• Beta diversity of birds is concentrated in mountain ranges

  • The variation is altitude allows for different species to exist

  • This works since birds are so mobile

IUCN Red List

• Union for conservation of nature

• Highlight species that are likely to go extinct in time for conservationist to take action to preserve them

What is causing the current extinction?

Hunting, habitat degradation, climate change, overexploitation, non-native species

Why protect biodiversity

• Humans should protect the genetic library of natural ecosystems

• Ecosystems provide a broad set of services that humans rely on for our welfare

• Aesthetic and ethical obligation to protect our planet

Species richness

The number of species in a specified area

Island biogeography

• Larger islands tend to have more species

• Immigration, extinction, evolution determine species richness

• There cannot be more immigration if the island cannot support more species

• The more species there are, the more extinction there will be

Equilibrium theory of island biogeography

• There is a sweet spot between immigration and extinction that predicts the equilibrium species richness

  • The number of species found on an island when immigration and extinction rates are equal

• The intersection also predicts the rate at which new species replace extinct species

Equilibrium turnover rate

The rate at which the composition of the species on an island changes over time

• As island size increases, number of species increases

• As distance from the mainland increases, the number of species decreases

Issues with equilibrium theory

• Few communities every attain equilibrium species richness

  • disturbances, evolution

• Islands are not homogenous patches sitting within a featureless seascape

  • Wind patterns

• Species are not interchangeable

  • Species success depends on biology and interactions 

Corridors

Routes that virtually all members of a taxon can cross

Filters

Routes that selectively prevent some species from crossing while allowing other species through

Sweepstakes routes

Habitats that are nearly impossible for most species to cross except during rare and unpredictable circumstances

Overcoming dispersal barriers

• Jump dispersal

  • Many individuals of a species jump the barrier all at once

• Diffuse through corridors of dispersal

Secular migration

Species’ range expansion that occurs over many generations and which takes so long that the species evolve enroute

Species-Area curves

• Islands have fewer species per unit area and a steeper species-area curve than mainlands

• Populations are less likely to go extinct in larger areas

• Larger areas contain more types of habitat

Species-habitat diversity hypothesis

Larger areas contain more species because they tend to contain more distinct habitats and thus can support more different species with specialized habitat requirements

Population rescue

Occurs when a population might go extinct on its own but immigrants join the population and thereby prevent extinction

Vicariance

Splitting of once contiguous population into two or more ranges

Allopatric speciation

Two populations of the sma species become geographically isolated. Populations diverge because selection and drift

Historical geographers assume that many broad biogeographic patterns were initiated by either dispersal or vicariance events

Sympatric speciation

Geographic isolation is not a prerequisite for speciation. Can occur when disruptive selection is strong and supported by mate choice. Can also occur when a mutation or hybridization produces a large-scale change in chromosome numbers

Great american biotic interchange

• The exchange of terrestrial fauna and flora between north and south america that resulted from the emergence of the isthmus of panama

• 50% of SA was north

• 10% of NA was south

Human accelerated dispersal

• Introduced species often lead to extinction of native species and loss of biodiversity

• Many if the same species are introduced over and over again, many areas of earth are losing their distinctive nature

Latitudinal hypothesis

• Regional energy availability

  • Regions with more solar energy will have more photosynthesis and more biologically available energy

• Water availability

  • Water availability will limit species richness

• NPP

  • Photosynthesis is limited by water and solar energy

• Habitat diversity

  • More plant species provide more food and thus supports more species

• AET is the best predictor of tree species richness

Biodiversity hotspots

Exceptional concentrations of endemic species and extensive habitual loss

• The closer you are to the equator, the more direct the sun hits

• The more direct angle, the more sunlight, the more heat, summer

Wind cells

Hot air at the equator rises and then cools to form clouds. The clouds fall as rain towards the tropics. The dry air is pushed towards the poles, it then cools a lot more and falls back to the earth. The dry, dense air flows towards the equator.

Coriolis effect

• Apparent deflection of object moving across a rotating sphere

• Looks like is it being left behind