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 –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)

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

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

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

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

Case Study 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 Pakeman RJ. Plant migration rates and seed dispersal mechanisms. Journal of Biogeography. 2001;28:

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

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

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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