Dispersal

"Three fundamental processes of Biogeography"

• Speciation
• Extinction
• Dispersal: movement beyond distribution limits

• Dispersalist: C. Darwin, A.R. Wallace, A. Gray
• Extensionist: C. Lyell, E. Forbes, J. Hooker (Vicariance)

• Movement to new, unused resources (away from parents)
  • Within same habitat
  • Across barrier to new habitat (within range)

• Rare and infrequent, seldom observed
• Fundamental process of biogeography
• Common in the fossil record (minimum age)

• "long distance" transport
• withstanding unfavorable conditions during travel and upon early arrival
• establishing a viable population

Three Kinds of Dispersal Leading to Range Expansion

• Jump Dispersal
• Diffusion
• Secular Migration

• Jump Dispersal: long distances over inhospitable habitat
  
  • example: oceanic islands
  • mostly by volant organisms (flight) ex.: Galapagos Islands
  • rare, large (distance), and "surprising" events
  • explains large discontinuous distributions of some organisms
  • explains taxonomic similarity of distant biotas and populations

• Diffusion: movement into adjacent habitats as population expands [overkill] [Carya]
  • Plants: purple loosestrife, halogeton, storksbill
  • Birds: cattle egret, starlings, house sparrows
  • muskrat, armadillo, nutria (Myocastor coypus) + [map]

• Secular Migration: geological times scale
  • Plants: diversification and spread of flowering plants
  • Animals: spread of camels from North America to S. America and Asia

• Active Dispersal
  • strong fliers
  • annual migrators
  • examples: golden plover, monarch butterfly

Log Normal
Normal
Exponential


Adaptive advantage

• Resistant seeds, spores (floating on salt water)
• Tiny size for distant transport by wind
• hitchhikers (phoresy): hooks, hairs for transport by animals
  • animal hitchhikers: flower mites in hummingbird noses

• Physical
  • human introductions indicate how effective barriers can be (bass in Caribbean)
  • overcome resistant propagules
  • "weeds" are good dispersers (hardy)
• Physiological
  • land-water
  • salinity for aquatic organisms
  • temperature both low and high (sky islands)
• Ecological-Behavioral
  • predators
  • strong fliers that won't cross water

• Corridors: favorable habitat connecting larger ones
  
  • Tethyan Sea
  • Bering Land Bridge [map]
  • Panama Isthmus

• Filters:blocks or slows passage of some organisms
  
  • Arabian desert allows movement of animals between Africa and Asia
  • Sunda archipelago reptiles
  • Southwestern forest vertebrates [SW]
  • Panama: freshwater separates Caribbean from Pacific

• Sweepstakes Routes: severe barrier that permits rare dispersals
  
  • Asian snails in the South Pacific
  • South American animals in the Galapagos
• Plate Tectonics
  • Indian fauna introduced to Asia
  • Terranes

• Appropriate Habitat - Niche
• Propagule (minimum unit)
  • asexually reproducing plants
  • parthenogenetic geckos
  • gravid females

• pagile: distributed passively.
• parthenogenetic: females developing eggs capable of producing adults, without male fertilization.
• phoresy: the transport of organisms by other organisms
• propagule: any part of an organism (colony of organisms) or life stage of its life cycle that can reproduce the species and establish a new population (distribule)
• vagile: capable of active dispersal
• volant: capable of sustained flight