May 7: Dispersal and Barriers
Types of dispersal
- Active dispersal
- Waif dispersal
- Passive dispersal
- Diaspores
- Examples
- Negative exponential distribution
Characteristics of good dispersers
- short life
- rapid growth
- early maturity
- many small offspring
- little parental care or protection
- little investment in individula offspring
- adapted to unstable environments
- "pioneer" species
- niche generalists
- occupy low trophic level
- often self fertilize
- have large seeds, winged seeds, etc.
Barriers
Dispersal routes
Relative Dispersal Capabilities
Angiosperms (flowering plants)
- Unlimited: sea-water distributed plants (coconut, mangroves, beach plants)
- Excellent: seeds or fruits with adhesive qualities (burweed), parachute mechanisms (asters), or tiny windborne seeds (orchids)
- Very good: aquatic plants with seeds imbedded in mud (sedges, rushes)
- Good: fleshy fruits eaten by birds (fuschia, lobelias)
- Fair: fleshy fruits with medium-sized seeds (rubiaceae, mulberry)
- Poor: large seeds and fruits (oaks, plums, walnuts, mangoes)
Conifers:
- junipers: 1500 km from N. America to Bermuda to Europe to Azores
- pines: very short distances, although pine seeds can be carried across water
Birds: >3200 km (N. America to Hawaii)
Bats: >3200 km (N. America to Hawaii)
Land molluscs: >3200 km (Polynesia)
Insects and spiders: > 3200 km
Freshwater fish: only a few km across saltwater
Reptiles:
- Lizards: long distances for geckos
- Snakes: >800 km to Galapagos
- Land Tortoises: . 800 km to Galapagos
Amphibians: probably only small distances
Land Mammals:
- Rodents: >800 km to Galapagos
- Small mammals: >300 km Madagascar civets and insectivores
- Large mammals: ca. 40 km, semi-aquatic hippo on Madagascar