Module #7: Dispersal

Question 1

Dispersal vs. Migration

Answer 1

Dispersal: movement of organisms’ outside their existing range to colonize a new area

Migration: movement of individuals within an organism’s range, from population to population

Question 2

Propagule

Answer 2

The organismal unit that does the dispersing or migration, such as a seed or spore

Question 3

Types of dispersal (3)

Answer 3

Jump dispersal: movement over long distances, across hostile terrain, takes less than the individual’s lifespan

Diffusion: gradual spread, many generations, across hospitable terrain

Secular migration: spread of shift of species range very slowly, geological time scale, so that species undergoes evolutionary change and differs from ancestral population in source area. Can occur over thousands of years.

Question 4

Random Walk

Answer 4

A mathmatical formulation of a trajectory that consists of taking successive random steps

Question 5

Levy Flight

Answer 5

A random walk in which the step-lengths have a probability distribution that is heavily tailed

Question 6

Plant dispersal strategies

Answer 6

-seeds and spores resistant to water, concussion, abrasion, etc.
-tiny size or have wings, fibers for transport by wind
-hooks, hairs, spines for transport by animals (hitchhikers)

Question 7

Agents of seed dispersal: Physical

Answer 7

-Anemochory: wind dispersal
-Thalassochory: sea dispersal
-Hydrochory: freshwater dispersal

Question 8

Agents of seed dispersal: Biological

Answer 8

-Biochory: movement by other organisms
-Ichthyochory: movement by fish

Question 9

Good vs. bad dispersing organisms

Answer 9

Best: birds, bats, insects, spiders
Average: lizards, tortoise, rodents
Worst: freshwater fish, large mammals (can’t cross water)

*dispersal ability doesn’t guarantee it will survive in the new area once it gets there

Question 10

Failed dispersers

Answer 10

Either could not move a long distance, withstand environment during travel/on arrival, or could not establish a viable population

ex: new zealand has no kangaroos, since they cant fly or swim to NZ from australia

Question 11

Reluctant dispersers

Answer 11

May maintain a new colony but do not spread in the new location

Ex: toad in Ireland comes from England, but it never spreads

Question 12

Rampant dispersers

Answer 12

invasive exotic creatures (ex: european starling, purple loosetrife)

*successful invaders depend on lower species diversity and human-made habitats (disturbed sites)!

Question 13

Why is landscape ecology relevant to dispersal?

Answer 13

The arrangement of landscape elements in a landscape mosaic affects the ease with which organisms may move through a landscape

Question 14

Landscape resistance

Answer 14

Describes the ease of movement of organisms through the landscape

*specific to each species, what affects one species may not affect another

Question 15

Patch-corridor-matrix Model

Answer 15

Often used in landscape ecology to explain species patterns and dynamics.

1) Patch: fairly uniform area that differs from its surroundings

-patch size affects the occurrence of species
-more edge species (generalists) found in smaller patches
-more specialists found in larger patches (more interior land)

2) Corridor: strip of land/water that differs from the area on either side and links together patches

3) Matrix: background ecosystem or land-use type in which the patches and corridors are found

Question 16

Barriers to dispersal (Simpson 1940)

Answer 16

Levels of dispersal difficulty:

Level 1: Corridors: Routes through hospitable terrain that allows unhindered passage in both directions

Level 2: Filter routes: Some migrants are barred, like the Alaska/Siberia land bridge during the Pleistocene during the Arctic climate

Level 3: Sweepstakes routes: Small number of winners, or those that manage to survive the journey to colonize a distant place

Question 17

Panama – Panamanian Land Bridge

Answer 17

For most of the past 65 million years, Panama was an island. Around 3 million years ago, the Panamanian land bridge developed and allowed increased interchange of North/South American plants and animals.

-Panama was considered a filter because some animals were barred from passing
-Migration was much more successful for those that moved south

Results of faunal exchange for mammals:
-diversity of north america remained the same, but diversity in south america increased
-many south american animals went exinct
-currently 50% of south american animals are from the north, while only 10% of current north american animals are from the south