1. Chapter 8
February 27, 2012

2. Three fundamental processes in biogeography: evolution, extinction, and dispersal
Dispersalists vs Extensionists
Continental Drift
Dispersalists vs Vicariance biogeographers
Bejerinck’s Law: “Everything is everywhere, but the environment selects”

3. Dispersal – the movement of organisms away from their point of origin
Intra-range dispersal – movement from place of origin to new site within the current range of the species
Extra-range dispersal – movement for place of origin to new site outside the current range of the species
Dispersal as an Ecological Process:
Natural Selection favors individuals that move a modest distance from their birthplace
This prevents competition with parents and siblings
Dispersal as a Historical Biogeographic Event
Dispersal reconstructed using living and fossil representatives

4. Passive dispersal – requires outside force to move propagule
Barnacles attach to ships and turtles
Active dispersal – the propagule moves itself
Cattle egret – flew 200km across the Atlantic Ocean from Africa to South America in late 1800s
Elephants can
swim 10km
Dwarf mistletoe –
projectile seeds
travel several meters

5. Passive Dispersal Anemochores – dispersed by the wind
Island insects, bats, and birds
Hydrochores – dispersed by water
Coconut palm – seed stays afloat for long periods – shell is salt proof
Anemohydrochores – dispersed by wind or water
Zoochores – dispersed by animals
Exo-zoochory – seed carried on fur or clothing
Endo-zoochory – seeds carried inside an animal

6. Passive Dispersal
North American beech (Fagus grandifolia) and passenger pigeon (Ectopistes migratorius)
Joshua tree (Yucca bevifolia) and giant
ground sloth
Anthropochores –
zoochores that are
dispersed by humans
Crops, weeds

7. The Best Dispersers
Supertramps – organisms well suited for rapid dispersal and successful colonization
Generalists
Common on disturbed sites
Most are passive dispersers
dandelions

8. Dispersal and Range Expansion
Range expansion categorized as colonization or invasion
Colonization – propagule arrives in previously unoccupied area and establishes a reproducing population
To expand its range, a species must be able to
Travel to a new area
Withstand potentially unfavorable conditions during its passage
Establish viable populations upon its arrival
The 3 mechanisms of range expansion are jump dispersal, diffusion, and secular migration

9. Mechanisms of Range Expansion
Jump dispersal – long-distance dispersal with individuals establishing kilometers away from their original range limits
Krakatau in 1883 – all life destroyed
1933 (50 years later) – island covered in dense tropical forest, 271 plant species, 31 bird species, and numerous invertebrates
Dispersed across 40-80km of water from neighboring islands
Hawaii is 4000km west of North America

11. Mechanisms of Range Expansion
Diffusion – a slower form of range expansion that involves populations
Takes generations to accomplish
Armadillo (Dasypus novemcinctus) took 100 years to spread from the Mexican border to Arkansas
Starlings (Sturnus vulgaris) introduced to New York in 1891 – reached west coast by 1980

12. Mechanisms of Range Expansion
Secular migration – takes hundreds of generations so that species evolve en route
Northward expansion of eastern hemlock (Tsuga canadensis) after the last ice age took thousands of years
North American horses and camels
Hippidion one-toed horse
Ancestral camel Poebrotherium