Lecture Seven - Migration and Dispersal

Question 1

What is the difference between migration and dispersal?

Answer 1

• 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.

Question 2

Define migration.

Answer 2

Mass directional movements of large numbers from one location to another.

Question 3

Define dispersal.

Answer 3

Spreading of individuals away from others.

Question 4

Give the three phases of migration and dispersal.

Answer 4

1) Emigration
2) Transfer
3) Immigration

Question 5

What are some reasons for migration?

Answer 5

• 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.

Question 6

What might be the reason for migrating to track food or favourable habitat?

Answer 6

Resources are in different places at different times.

Question 7

Describe the threats to the Monarch butterfly.

Answer 7

• Intensive agriculture
• Logging
• Climate change

Question 8

How does climate correlate to survival of the Monarch butterfly?

Answer 8

Warm and wet conditions through the winter lead to reduced survival.

Question 9

Describe the migratory behaviour of the Giant Panda.

Answer 9

In summer, pandas migrate to greater altitude to exploit a different species of bamboo.

Question 10

Name the convention for migratory species.

Answer 10

The Bonn Convention / Convention on the Conservation of Migratory Species of wild animals

Question 11

What is natal dispersal?

Answer 11

Dispersal from where born to where breeding takes place.

Question 12

Give a method of passive dispersal.

Answer 12

Seed rain.

Question 13

Give three methods that seeds take advantage of passive dispersal.

Answer 13

• Exploding seeds
• Winged seeds
• Seeds with feathery parachutes

Question 14

Give two forms of seeds that are likely to be dispersed by an active or mutualistic agent.

Answer 14

• Spiny/prickly seeds, get stuck to animal fur.

- Fleshy edible fruits, transported through their predators.

Question 15

What is the advantage of movement through an active or mutualistic agent?

Answer 15

Reduces the uncertainty of destination

Question 16

Describe the dispersal of Prunus mahaleb.

Answer 16

• Birds allow shorter distance seed dispersal to woodland.

- Mammals allow longer distance dispersal to open habitats.

Question 17

What is dispersal polymorphism?

Answer 17

May produce multiple seed types or offspring types to allow for successful dispersal.

Question 18

When is dispersal polymorphism normally present?

Answer 18

In variable or unpredictable habitats

Question 19

Give an example of dispersal polymorphism in insects.

Answer 19

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.

Question 20

What is the disadvantage of winged morphs?

Answer 20

• Longer development times
• Lower fecundity
• Shorter lifespans

Question 21

What is the general pattern of dispersal distance?

Answer 21

Many individuals dispersed long distance, few dispersed long distance.

Question 22

What is expected for passive dispersal?

Answer 22

Diffusion from areas of high to low density.

Question 23

What might be a reason for more species being found dispersing short distances?

Answer 23

Short-distance movements are more detectable; no accurate quantifications on how many individuals travelled long distances.

Question 24

What percentage of Bird Cherry-Oat Aphids find hosts during autumn dispersal?

Answer 24

0.6% (Ward et. al)

Question 25

Why disperse?

Answer 25

• Opportunity to be successful

- A change to colonise an area with conditions that aren’t being exploited yet / there is no competition

Question 26

Describe the reason for dispersal in Heath fritillary larvae.

Answer 26

• 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.

Question 27

Give some reasons for dispersal.

Answer 27

• To exploit resources
• To escape intraspecific competition (density-dependent emigration)
• Inbreeding avoidance
• Avoiding kin competition

Question 28

What might local adaptation within a species lead to?

Answer 28

Outbreeding depression

Question 29

Give a species that disperses in order to escape kin competition.

Answer 29

Californian Mouse.

Mean female dispersal distance increases with increasing numbers of sisters in litter.

Question 30

Give some consequences of dispersal.

Answer 30

• Change in local population size
• Dispersion is risky; not all emigrants immigrate.
• Can lead to Source-Sink Dynamics

Question 31

What are Source-Sink Dynamics?

Answer 31

The size of a population does not reflect local carrying capacity; in sink populations, death rate is greater than birth rate.

Question 32

What can save sink populations from extinction?

Answer 32

If I - E > D - B

I = immigration rate
E = emigration rate
D = death rate
B = birth rate

Question 33

Give an evidence for source sinks within a species.

Answer 33

Pied Flycatcher populations in North Finland require immigration from the South to survive.