L5: Dispersal

Question 1

What is dispersal?

Answer 1

Dispersal is the movement of organisms away from their point of origin.

Question 2

To expand its range, a species must be able to:

Answer 2

1) Travel to a new area.
2) Withstand potentially unfavourable conditions during its passage.
3) Establish a viable population upon arrival.

Question 3

Types of dispersal

Jump dispersal (or long-distant dispersal)

What is an example?

Answer 3

Dispersal that is accomplished by movement of individuals within relatively short period.
Kms or miles away

An example can be seen in the rapid colonization of Krakatau islands after a volcanic eruption (1883) removed two- thirds of the largest island (Rakata) and buried all three islands in a blanket of volcanic ash, eliminating life from their land surfaces.

Question 4

What is jump dispersal good for?

Answer 4

1) to explain the wide, and often discontinuous, distribution of many taxa.

2) To account for the similarities and differences among biotas inhabiting
widely separated, but similar, habitats.

3) It emphasizes the importance of anthropogenic long-distance transport of species.

Question 5

Types of dispersal

Diffusion

Example?

Answer 5

A form of range expansion that is accomplished over generations by individuals spreading out from the margins of the species range.

E.g range expansion of the starling after their intentional introduction into North America

Question 6

Difference between diffusion compared to jump dispersal

Answer 6

Much slower than jump dispersal! Over generations by populations gradually spreading out from the margins of a species’ range.
But often follows jump dispersal.

Question 7

Types of dispersal

Secular migration

Answer 7

Geographic range expansion, which is so slow (e.g. many generations!) that it is often accompanied by substantial evolutionary changes in the population en route.
They expand to colonize new regions.
Similar to diffusion.

Question 8

Types of mechanism of movement

Active dispersal vs Passive dispersal

Answer 8

Passive aeolian- helicopter seeds, bugs, pollen
Active aeolian- bats, birds, moths/ butterflies

Passive aquatic- lizard on a floating log
Active aquatic- swimming mammals/ amphibians

Question 9

Difference between active and passive

Answer 9

Active: movement of an organism from one location to another by its own means.

Passive: movement of an organism from one place to another by means of a stronger force, such as water flow, wind or another organism.

Question 10

Example of Active dispersal

Air

Answer 10

Air:
• Flight-migratory routes
• Effective active dispersal

e.g. The annual migration of North America’s monarch butterfly

Question 11

Vast majority of organisms disperse largely by…

Answer 11

passive dispersal.

Question 12

Examples of passive dispersal

Answer 12

Wind
- Dandelion

Animals
- Blackberry

Water
- Coconut

Question 13

What are barriers?

Answer 13

Any abiotic or biotic feature that totally or partially restricts the movement of genes or individuals from one population or locality to another.

Barriers are species-specific phenomena

Question 14

Barriers and dispersal routes

Answer 14

1) Corridors
2) Filters
3) Sweepstake routes

Question 15

What are corridors?

Answer 15

Dispersal route that permits the movement of many (or most) species of a taxon from one region to another. No selectively discriminate against any form.

Biota from both sites of the corridor share the same taxonomic or functional groups. Free communication.

Question 16

What are filters?

Answer 16

Dispersal route that is more restrictive than a corridor. It selectively blocks the passage of certain forms while allowing those able to tolerate the conditions of the barrier to migrate freely.

Biota from both sites of the filter share many of the same taxonomic or functional groups.

Question 17

What are sweepstakes routes?

Answer 17

A severe barrier that results in the partly stochastic (by chance) dispersal of some elements of a biota, and the establishment of a disharmonic biota.

Question 18

What is vicariance?

Answer 18

Attempts to reconstruct the historical events that led to observed distributional pattern based largely on the assumption that these patterns resulted from the splitting (vicariance) of areas and not long-distance dispersal.

Geographical range of a taxa is split into parts by the formation of a barrier –no dispersal!
Geological/ climatic events

Question 19

What are the three types of dispersal?

Answer 19

Jump dispersal

Diffusion

Secular migration

Question 20

What is mentionable about active dispersal in water?

Answer 20

It’s less effective- the organisms are forced to swim through unfavourable habitats.

Question 21

Example of a filter?

Answer 21

Filters across archipelagos that connect different biogeographic kingdoms…

e.g Indonesia (Australian- Oriental) and Aleutian (Palearctic-Nearctic).