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)
Why disperse?
- Opportunity to be successful
- A change to colonise an area with conditions that aren’t being exploited yet / there is no competition
Describe the reason for dispersal in Heath fritillary larvae.
- They feed on Cow Wheat in woodland clearings, in early woodland succession stages.
- Must colonise new clearings before their current habitats become overgrown, and there is no source of food available.
Give some reasons for dispersal.
- To exploit resources
- To escape intraspecific competition (density-dependent emigration)
- Inbreeding avoidance
- Avoiding kin competition
What might local adaptation within a species lead to?
Outbreeding depression
Give a species that disperses in order to escape kin competition.
Californian Mouse.
Mean female dispersal distance increases with increasing numbers of sisters in litter.
Give some consequences of dispersal.
- Change in local population size
- Dispersion is risky; not all emigrants immigrate.
- Can lead to Source-Sink Dynamics
What are Source-Sink Dynamics?
The size of a population does not reflect local carrying capacity; in sink populations, death rate is greater than birth rate.
What can save sink populations from extinction?
If I - E > D - B
I = immigration rate E = emigration rate D = death rate B = birth rate
Give an evidence for source sinks within a species.
Pied Flycatcher populations in North Finland require immigration from the South to survive.
