Dispersal

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Dispersal
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• Propagule
• Any plant material used for the purpose of plant
  propagation
• Asexual reproduction a propagule twig or leaf
  section
• Sexual reproduction a seed
• Dispersal
• Movement of an organism away from its point of
  origin
• I. Intra-range dispersal (ecological dispersal)
• Decreases competition with parents
• Example shade intolerant pine trees must
  distribute seeds
• to new disturbed sites
• II. Extra-range dispersal (biogeographical
  dispersal)
• Movement to a site outside the current
  geographical range
• Colonization of new regions

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• Passive dispersal
• Outside physical force required to move the
  propagule
• Wind, water, birds, mammals
• Most plants are obligate passive dispersers
• Some animals (planktonic invertebrate larvae and
  barnacles)

Planktonic stage of crab larvae
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Active dispersal Mainly restricted to animals
Exceptions Dwarf mistletoe and squirting
cucumber exhibit ballistic dispersal
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• Modes of passive dispersal
• Anemochores
• Dispersed by the wind
• Samara seeds of maple
• (Acer spp.) and certain pines (Pinus spp.)

Light (very little endosperm) More seeds, but
less resistant to dessication Random movement
(may land on inhospitable sites)
Acer saccharinum
Pinus sylvestris
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The advantage of investing in larger seeds
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• More anemochores Tufts of hair-like material
• Taraxacum officinale (dandelions) and Populus
  spp. (cottonwood, poplar and aspen)
• Rolling of tumbleweed (Salsola iberica)
• Web strands of black widow spiders (Lactrodectus
  mactans)

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• Hydrochores (thalassochores)
• Dispersed by moving water
• Adults, larvae and eggs of many aquatic organisms
• Crabs and starfish have planktonic juvenile stage
• The coconut palms (Cocos nucifera) husk and
  shell protect the seed from salt water for long
  time periods

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• Anemohydrochores
• Dispersed by wind or water
• (eg. cottonwood)
• Zoochores
• Dispersed by animals
• Spikes that hook into
• fur or clothing
• (eg., ragweed
• Ambrosia spp.)
• Burclover
• (Medicago polymorpha)
• and garden vines
• (Plumbago spp.)
• Birds and squirrels
• store acorn seeds or

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Anemochory and Zoochory Not much to
choose between them What are the advantages and
disadvantages of each?
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• Endo-zoochory
• Seeds pass through animals digestive tract
• Generally larger seeds with more endosperm
• Fewer seeds and more costly to reproduce, but
  more likely to end up at hospitable sites for
  growth
• Susceptible to reduced dispersal if transporting
  species goes extinct

Bird feeding on a seed pod of Stenocereus
thurberi (organ pipe cactus)
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Endozoochorous fungi Pilobolus spp.
Pilobolus spp. spores
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• Anthropochores
• Dispersed by humans
• Ribwort (Plantago lanceolata) Sticky seeds
  carried by clothing or fur

Many plants possess burrs, for transport by
either human clothing or animal fur
Goose grass
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Colonization - Krakatau
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Eastern Hemlock (Tsuga canadensis)
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Stepping stone migration
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Migration and Irruption Episodic explosions in
population size
dN / dt rN
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Logistic population growth curves
dN / dt rN (K-N) / N)
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Long distance migration Cattle egret
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Invasive species
American muskrat
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Purple loosestrife
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The Impact of Climate Change On Dispersal and
Ecozone Distribution