General Ecology: Lecture 2
October 1, 2003
I.
II.
III.
Overview: The problem of distribution
Approach for examining the problem of distribution.
A.
Can the species survive outside the range where it is found?
1.
Test with transplant experiments [Fig. 3.2]
a)
Description
b)
Controls
2.
If yes, why isn’t it found there?
a)
Key: Dispersal
3.
If no, what limits it?
a)
Interactions with other species, such as competition and predation
b)
Physical factors, such as temperature and moisture.

NOTE: As a behavioral ecologist, I interpret the habitat
selection issue differently than the author. Habitat choice is
always related to the presence/absence of particular
interactions with other organisms, or with physical features,
and should not be considered a separate category that limits the
distribution. For example, the need for a particular set of
circumstances to perform a behavior (i.e. a high perch to
perform a display behavior) is not qualitatively different than
the requirement for a certain type of food, nest building
material, etc… It is a biological need of the animal. Hence, we
are skipping Chapter 5, and will cover this material in the
context of interrelationships and physical factors.

Shelford’s law of tolerance

Physiological ecologists test the limits of particular species to
particular environmental factors such as temperature, moisture,
pH, oxygen levels, etc…

Complicating factors

Physiological acclimation [Fig. 3.3]

Life stage (which one is usually most sensitive?).

Natural selection (think about different populations)
c)
Summary figure [p. 38]
Factors that Limit Distributions: Dispersal (Ch. 4)
A.
Results of dispersal
1.
Ecological process/consequences
2.
Genetic/evolutionary process/consequences
B.
Mechanisms of dispersal
1.
Several examples
2.
Focus: Human-caused dispersal
a)
Example: Zebra Mussels

General description of the organism

Major effects of zebra mussels

C.
D.
Pathway and timing of dispersal for the zebra mussels [Fig.
4.1]

Hypothesis

Patterns of colonization.

Movement between river systems
Describing, modeling and predicting dispersal
1.
Basic modes of dispersal
a)
Diffusion
b)
Jump dispersal
c)
Secular dispersal
2.
Reid’s Paradox

Description of the paradox, including the diffusion model

Discrepancy “solved”. How? [See Fig. 4.5]
3.
Barriers to dispersal
a)
Some examples
4.
Statistical generalization: Tens rule [Box 4.1]
a)
Greater chance for imported organisms to become established on
islands. Why? A couple of hints for Question Set 1…
5.
Barriers to dispersal allow unique faunas to develop
a)
Example: Marsupials vs. placental mammals in South America
6.
Disjunct (geographically non-contiguous) populations
a)
Example of likely vicariance: Distribution of Antarctic beech
(Nothofagus) [Fig. 4.7]
7.
Note that such a disjunct population could be caused by the movement of
populations across pre-existing barriers (jump dispersal). Need knowledge
of continental movement and other geological changes to sort these out.
Evolutionary advantages of dispersal (if time)
1.
Costs and benefits
2.
Example: Jellies
Study questions
1.
What type of experiment is generally used to decide whether a species can survive (and
reproduce) outside of its geographic range? Briefly describe one type of control you need
to do as part of this experiment.
2.
If a species can survive and reproduce outside of its geographic range, what is likely reason
it is not there?
3.
If a species cannot survive outside of its geographic range, list some reasons why it is
unable to do so.
4.
State Shelford’s Law of Tolerance in your own words. Discuss whether this is really a
scientific “law”.
5.
You hypothesize that pH of the water is the key physical factor that limits the geographic
range of the wild hump-backed catfish. Outline an approach for testing your idea, being
sure to take into account the “complicating factors” that make this a challenge.
6.
What key concepts about tolerance to temperature in the arctic char can be gleaned from
Fig. 3.3? Be sure you can read and understand this type of graph.
7.
Describe several mechanisms by which organisms disperse.
8.
Why is dispersal considered to be an ecological process? How does it also act as
genetic/evolutionary process?
9.
From where did zebra mussels originate, and how are they hypothesized to have reached
the U.S.?
10.
Describe the key effects that zebra mussels have had on the ecosystems they have invaded.
11.
List and describe the three basic modes of dispersal.
12.
Explain the diffusion equation in words, creating a verbal description that a high school
student could understand.
13.
Describe Reid’s paradox and its “solution” in your own words.
14.
Describe some barriers to dispersal.
15.
How are dispersal barriers related to the rise and fall of marsupials in South America?
16.
What are the two possible mechanisms by which “disjunct” (geographically noncontiguous) distributions of species can arise? Provide examples of each.
17.
Define “vicariance”. (Hopefully, you used the word in the above question!)