Chapter 8

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

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