General Ecology: Lecture 8
October 14, 2005
Today’s topic: Intraspecific competition (cont. from Lecture 7))
I.
Mechanisms of population regulation
A.
Role of stress (see Part 1 handout)
B.
Role of dispersal
1.
Potential benefits of dispersal a) In the context of intraspecific competition, dispersal provides potential for locating a less crowded environment with abundant resources and less competition . In terms of fitness, individuals could benefit by
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Higher growth rates
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Higher fecundity
Avoid competition with kin. Why important?

Kin selection: According to this concept, one’s own fitness is determined not only by one’s own offspring, but also by a kin component that counts the offspring of close relatives that wouldn’t have made it without your help.
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Current level of competition will determine importance of dispersal
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Example: water striders
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In many species, young adults cannot find breeding territories or mates unless they disperse. b) Establishes new populations
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Why important?
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How could this benefit the individual’s fitness? c) Outbreeding: creates new genetic combinations
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Why important?
 How could this benefit the individual’s fitness?
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NOTE: These new populations have a subset of the genes in the entire population.
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Founder effect: Only a small proportion of the population disperses, so there’s a very slim chance that all genotypes would be transferred to any one new location
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There is some evidence that some genotypes may be predisposed to disperse (no literature cited)
2.
Costs of dispersal a) May never locate suitable habitat b) Higher risks associated with the dispersal journey itself c) Hybrids from outbreeding may be less able to adapt
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Outbreeding depression
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What is this? d) Subset of alleles of the dispersers may, by chance, be less suited to the new environment. e) Loss of kin associations f) Loss of adaptive social traditions.

3.
Types of dispersal a) Presaturation dispersal
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When does it occur?
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Who participates? b) Saturation dispersal
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When does it occur?
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Who participates?
4.
Sink habitats a) What is a sink habitat b) Example: conch populations in Florida
5.
NOTE: We won’t discuss the work done on voles by Krebs and his colleagues
“Does Dispersal Regulate Populations Some quite complex experimental design is involved that we simply don’t have time to cover adequately
C.
Social interactions (focus on aspects related to intraspecific competition)
1.
Social dominance a) What is it and why is it important? b) What type of competition do social dominance hierarchies represent? c) When are these behaviors most likely to be strongly expressed?
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Example: pack size in wolf populations
2.
Territoriality a) Establishment of territories
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What are the major purposes of territories?
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What conditions lead to the establishment of territorial behaviors?
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Why are some species only territorial for portions of the year?
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Territoriality is linked to fitness
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Example: Elephant seals and territorial defense of breeding beaches.
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See also the aphid example in text b) Territorial behavior
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During territory establishment
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After mating/production of young has occurred
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Example: penguin colonies c) Territory size
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Costs/benefit analysis [Fig. 12.14 d) Relationship of habitat suitability, population density and fitness: an optimality model [Fig. 12.15]
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Key points e)
“Floaters”
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Example 1: bands of male lions
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Example 2: scrub jays—helpers at the nest
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Example 3: “sneaky” female-mimicking males
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Also see rufous-collared sparrow example in text.
D.
Density-independent influences (a brief re-cap)

Study questions
1.
List/explain the potential benefits of dispersal as specifically as possible. (Be sure you clearly explain the particular benefit, don’t just list it!). Be sure your explanation includes if/how it might enhance individual fitness.
2.
List/explain the potential costs of dispersal as specifically as possible. (Be sure you clearly explain the particular benefit, don’t just list it!). Be sure your explanation includes if/how it might enhance individual fitness.
3.
Explain the difference between pre-saturation and saturation dispersal, being sure to indicate what is happening to population growth at the time, as well as which population members tend to be the dispersers.
4.
What is a “sink” habitat? How can it be misleading if simply viewed from the perspective of population size?
5.
What type of competition are social dominance and territoriality considered to be? Explain. Under what conditions are dominance hierarchies most likely pronounced?
6.
How is it possible for population growth to be regulated via dominance hierarchies? Provide an example.
7.
What are the key purposes of a territory? What must be true about resource distribution in order for territories to be practical?
8.
What are the potential benefits of having a good territory? What are some of the costs? In terms of costs and benefits, what (in general terms) is the ideal size of a territory?
9.
Why are many/most territorial animals only territorial for portions of the year? Provide an example.
10.
Imagine that a male establishes and maintains a territory over a breeding season. When during that breeding season is his aggressive behavior towards those of his own species (conspecifics) likely to be more pronounced vs. when might act cooperatively with conspecifics? Explain in terms of his fitness.
11.
Be able to explain and interpret Figure 12.15
12.
Describe some of the alternate (or “floater”) behaviors displayed by sub-dominant individuals without their own territories.