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BIO120H1 Lecture Notes - Gamete, Motility, Inbreeding Depression

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Paul Thompson

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Causes and Consequences of Dispersal in Plants and Animals:
- Dispersal ecological process where individual or multiple individuals move away from the population in which they
were born to another location/population, where they settle and reproduce
- 2 common forms:
o natal dispersal first movement where it first attempts to reproduce (permanent)
o breeding dispersal changing location in space after reaching reproductive maturity, usually involving
movement from one habitat patch to another
- another type of dispersal: gamete dispersal (doesn’t fall into these categories) common for non-motile adults,
such as plants
****(relocation considered to be an adaptive trait)****
Active Dispersal:
movement of entire organism through its own ability and is common in both adult/juvenile animals
Degree of dispersal varies among species depending on factors and social structure
o Harem Breeding System: social systems that require a single male for reproduction (gorillas/primates)
and force most juvenile males to disperse since they aren’t all required
Is density-dependant process - depends on local pop size, resource competition, habitat quality/size
Consist of animals that highly vagile (able to move about or disperse in a given environment) most efficient at
active dispersal (birds, bats, large insects, large aquatic animals, terrestrial animals)
o For ex. Monarch butterfly fly many kilometers
Flying animals affected less by habitat changes they can bypass barriers by flying over them
o Fewer barriers on ocean than on land; aquatic animals can disperse better than land animals; land
animals expected to travel through unfavourable habitats with geographic barriers = inefficient
Passive Dispersal:
involves plants and animals that can’t move themselves but have dispersal units called disseminules to aid in
reproduction or the exploitation of new habitats
Many disseminules adapted for movement by specific dispersal agents available in the environment such as wind,
water or another animal capable of active dispersal, or species with more motile larval stage
o Sponges and corals (immobile marine invertebrates) have disseminules that are buds/cells used in
Corals reproduce by releasing gametes into water males gametes are motile and eggs move
via ocean currents
o Other aquatics have free-living juvenile stage where larvae drift near surface and are passively carried to
other locations
Plants disseminules include seeds, spores, and fruits all move away via environmental kinetic energy
o Distance traveled is result of velocity and direction of movement by dispersal agent
o Winds, flying animals or water currents most successful long-distance dispersal agents
Seeds and fruits with wings, hairs or inflated processes are carried by wind
o others have sticky or barbed seeds, or fruits, that adhere to feathers or fur of mobile animals
some seeds released over short distances or fall to base of plant
o on floor, animals compete for fruit/seeds seeds adapted to resist digestive juices and thus disperse
through feces
Why Disperse or Why Not?:
Animals that emigrate due to environmental conditions may get better habitat in new area
o Climate change affects dispersal as global climate changes, animal habitat ranges will shift
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