Lecture Seven - Migration and Dispersal Flashcards
What is the difference between migration and dispersal?
- Migration normally involves a population moving in the same direction
- Dispersal normally involves offspring moving from parents in different directions, e.g. in seed dispersal.
Define migration.
Mass directional movements of large numbers from one location to another.
Define dispersal.
Spreading of individuals away from others.
Give the three phases of migration and dispersal.
1) Emigration
2) Transfer
3) Immigration
What are some reasons for migration?
- Tracking food or favourable habitat, e.g. migratory birds
- Exploiting complementary habitats or resources, e.g. amphibians aquatic in spring and terrestrial rest of year.
- Tactical responses to overcrowding in unpredictable environments, e.g. locusts moving from arid regions.
What might be the reason for migrating to track food or favourable habitat?
Resources are in different places at different times.
Describe the threats to the Monarch butterfly.
- Intensive agriculture
- Logging
- Climate change
How does climate correlate to survival of the Monarch butterfly?
Warm and wet conditions through the winter lead to reduced survival.
Describe the migratory behaviour of the Giant Panda.
In summer, pandas migrate to greater altitude to exploit a different species of bamboo.
Name the convention for migratory species.
The Bonn Convention / Convention on the Conservation of Migratory Species of wild animals
What is natal dispersal?
Dispersal from where born to where breeding takes place.
Give a method of passive dispersal.
Seed rain.
Give three methods that seeds take advantage of passive dispersal.
- Exploding seeds
- Winged seeds
- Seeds with feathery parachutes
Give two forms of seeds that are likely to be dispersed by an active or mutualistic agent.
- Spiny/prickly seeds, get stuck to animal fur.
- Fleshy edible fruits, transported through their predators.
What is the advantage of movement through an active or mutualistic agent?
Reduces the uncertainty of destination
Describe the dispersal of Prunus mahaleb.
- Birds allow shorter distance seed dispersal to woodland.
- Mammals allow longer distance dispersal to open habitats.
What is dispersal polymorphism?
May produce multiple seed types or offspring types to allow for successful dispersal.
When is dispersal polymorphism normally present?
In variable or unpredictable habitats
Give an example of dispersal polymorphism in insects.
Aphids produced winger and unwinged forms.
In poor environmental conditions, produce more winged offspring so can search for suitable habitats.
In good conditions, will produce more unwinged offspring to take advantage of available local resources.
What is the disadvantage of winged morphs?
- Longer development times
- Lower fecundity
- Shorter lifespans
What is the general pattern of dispersal distance?
Many individuals dispersed long distance, few dispersed long distance.
What is expected for passive dispersal?
Diffusion from areas of high to low density.
What might be a reason for more species being found dispersing short distances?
Short-distance movements are more detectable; no accurate quantifications on how many individuals travelled long distances.
What percentage of Bird Cherry-Oat Aphids find hosts during autumn dispersal?
0.6% (Ward et. al)
