Mechanisms of Seed Dispersal

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Mechanisms of Seed Dispersal

• Jordan Rofkar
• Landscape Ecology
• 5/2/03

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Introduction

• Dispersal mechanisms
• Abiotic
• Biotic
• Seed Dispersal and Landscape Ecology
• Effects of fragmentation and corridors
• Modeling Seed Dispersal
• Case Study

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Mechanisms of Seed Dispersal

• Abiotic Mechanisms
• Water
• Seeds fall into flowing water and are carried to
  suitable habitat
• Explosion
• Capsule surrounding seed dries and bursts open
• Wind anemochory
• Morphological adaptations such as wings assist in
  dispersal

Mori SA, Brown JL (1994)
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Mechanisms of Seed Dispersal (cont.)

• Biotic Mechanisms
• Animals zoochory
• Endozoochorous Dispersal dispersal via the gut
  of an animal
• Ectozoochorous Dispersal dispersal on the
  outside on an animal
• Often results in co-evolution of plants and
  animal dispersers

http//www.fmnh.org/congo/phomam_mpusillus.html
http//www.stanford.edu/petelat1/
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Mechanisms (cont.)
A animal W wind E explosive N no apparent
adaptation for dispersal
Webb CO, Peart DR (2001)
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Dispersal and Landscape Ecology

• Fragmentation
• Infrequent long-distance dispersal (gt100 m) may
  lead to isolation or extinction
• Corridors
• Forested corridors may promote dispersal between
  patches due to mammal or bird movement

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Modeling

• LANDIS
• Spatially explicit simulation
• Effective and maximum dispersal distances for
  each species control distribution
• Establishment is modeled using an establishment
  coefficient

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Case Study
Pakeman RJ. Plant migration rates and seed
dispersal mechanisms. Journal of Biogeography.
200128795-800.

• Model-based study
• Observed migration rates are much greater than
  detectable dispersal rates ? Reids Paradox
• Result of only occasional long distance, chance
  dispersal events?
• Possible enhancement by zoochorous dispersal?
• Particular focus on endozoochorous dispersal

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Case Study (cont.)
Pakeman RJ. (2001)
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Case Study (cont.)
Variation in territory size almost linearly
affects dispersal rate.
Increasing probability of gut survival leads to
increased dispersal rates.
Tl 1000 Tl 5000
Pakeman RJ. (2001)
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Conclusions

• Gut passage times show that large herbivores can
  reach extent of territory and deposit seeds
• Model indicates that zoochorous dispersal is a
  potential explanation for discrepancies between
  observed plant migrations and measured seed
  dispersal rates
• Chance weather events may not necessarily be the
  only mechanism for long distance seed dispersal

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References

1. Yamada T, Suzuki E. Comparative morphology and
   allometry of winged diaspores among the Asian
   Sterculiaceae. J Trop Ecol. 1999 15619-635.
2. Mori SA, Brown JL. Report on wind dispersal in a
   lowland moist forest in central French Guiana.
   Brittonia. 1994 46(2) 105-125.
3. Web CO, Peart DR. High seed dispersal rates in
   faunally intact tropical rain forest theoretical
   and conservation implications. Ecology Letters.
   2001 4491-499.
4. Pakeman RJ. Plant migration rates and seed
   dispersal mechanisms. J of Biogeography. 2001
   28795-800.
5. Hewitt N, Kellman M. Tree seed dispersal among
   forest fragments I. Conifer plantations as seed
   traps. J of Biogeography. 2002 29337-349.
6. Hewitt N, Kellman M. Tree seed dispersal among
   forest fragments II. Dispersal abilities and
   biogeographical controls. J of Biogeography.
   2002 29351-363.
7. He HS, et al. A simulation study of landscape
   scale forest succession in northeastern China.
   Ecological Modeling. 2002 156153-166.