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Mechanisms of Seed Dispersal

Mechanisms of Seed Dispersal. Jordan Rofkar Landscape Ecology 5/2/03. Introduction. Dispersal mechanisms Abiotic Biotic Seed Dispersal and Landscape Ecology Effects of fragmentation and corridors Modeling Seed Dispersal Case Study. Mechanisms of Seed Dispersal. Abiotic Mechanisms

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Mechanisms of Seed Dispersal

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  1. Mechanisms of Seed Dispersal Jordan Rofkar Landscape Ecology 5/2/03

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

  3. 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)

  4. 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/

  5. Mechanisms (cont.) A = animal W = wind E = explosive N = no apparent adaptation for dispersal Webb CO, Peart DR (2001)

  6. Dispersal and Landscape Ecology • Fragmentation • Infrequent long-distance dispersal (>100 m) may lead to isolation or extinction • Corridors • Forested corridors may promote dispersal between patches due to mammal or bird movement

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

  8. Case Study Pakeman RJ. Plant migration rates and seed dispersal mechanisms. Journal of Biogeography. 2001;28:795-800. • Model-based study • Observed migration rates are much greater than detectable dispersal rates  Reid’s Paradox • Result of only occasional long distance, chance dispersal events? • Possible enhancement by zoochorous dispersal? • Particular focus on endozoochorous dispersal

  9. Case Study (cont.) Pakeman RJ. (2001)

  10. 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)

  11. 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

  12. References • Yamada T, Suzuki E. Comparative morphology and allometry of winged diaspores among the Asian Sterculiaceae. J Trop Ecol. 1999; 15:619-635. • Mori SA, Brown JL. Report on wind dispersal in a lowland moist forest in central French Guiana. Brittonia. 1994; 46(2): 105-125. • Web CO, Peart DR. High seed dispersal rates in faunally intact tropical rain forest: theoretical and conservation implications. Ecology Letters. 2001; 4:491-499. • Pakeman RJ. Plant migration rates and seed dispersal mechanisms. J of Biogeography. 2001; 28:795-800. • Hewitt N, Kellman M. Tree seed dispersal among forest fragments: I. Conifer plantations as seed traps. J of Biogeography. 2002; 29:337-349. • Hewitt N, Kellman M. Tree seed dispersal among forest fragments: II. Dispersal abilities and biogeographical controls. J of Biogeography. 2002; 29:351-363. • He HS, et al. A simulation study of landscape scale forest succession in northeastern China. Ecological Modeling. 2002; 156:153-166.

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