ICA 4 COMPETITION
Group Name _______________ Your name _______________
PART 1
1. How does intraspecific competition relate to density-dependent regulation of
population growth? Such competition increases with density and serves to dampen
population growth. 16.8
What are 4 negative density-dependent growth responses? slower growth; longer time
to reach sexual maturity, lower birth rate; higher death rate
2. Describe results for:
Fig. 1 A Body mass increases through time, up to a point when it levels off.
B The rate of increase in body mass is inversely related to population size.
Fig. 2 Age to sexual maturity increases with increasing population size.
Fig. 3 % of females reaching sexual maturity (having babies) declines with increasing
population size.
Fig. 5. Birth rate decreases and death rate increases with increasing population.
When B = D, the population size stabilizes.
3 What is the effect of intraspecific competition on r? It lowers r.
What is the effect of interspecific competition on K? It lowers K.
Fig. 6. 16.9 How much is K of sp 1 reduced by one individual of competing sp 2?
4X…by all individuals? competition coefficient 1,2 = 4; so 4xN = 4x4 = 16
Figure 7. What is the value of 1,2? = 4
PART 2
1. How is niche breadth affected by intraspecific competition? increases breadth
interspecific competition? decreases breadth
What is a consequence for the community of a reduction in niche breadth due to
competition? more species can exist in the community
2. What is meant by “the ghost of competition past”? Traits (niches) today may have
developed from competition in the past. Today no competition is evident.
How does the ghost make it hard to claim that competition explains the
present-day niche space of a species? Competition is no longer occurring because
past competition has resulted in a shift in niche to reduce competition.
3. What types of evidence are used to deduce that interspecific competition has occurred
in the past? Explain each.
A. niche separation; reduced or no niche overlap between species
B. habitat shift: no habitat sharing by close competitors;weaker species has changed
habitats.
C. character displacement; traits evolve to be different when two competing species
coexist.
D. competitor exclusion; only one species exists where two existed in the past
E. competitor release; competitor population size increases when a competitor has
been eliminated.
6. Fig. 9.What happens to niche overlap when closely related species co-occur? Each
species specializes on a unique part of the niche space.
Fig. 10. What happens to habitat use when closely related species co-occur? One
species moves to a different habitat
How would you test the hypothesis that 2 species don’t use the same part of the
habitat because of competition? remove species and see if other species moves in
Fig. 11. 17.16, 17.18 How do traits of two species compare when they co-occur vs.
when they do not? similar when non-co-occurring; different when co-occurring
Fig. 12. 16.7 What is the Competitive Exclusion Hypothesis? 2 species can’t coexist
on the same limiting resource; the better competitor will eliminate the weaker one.
Fig. 12A. 16.10 Under what conditions can two species coexist? Two species can
coexist if they are limited by different resources.
Fig. 14. Krill, shrimp-like organisms, are fed on by all large marine animals. What
does the killing of whales do to seal and penguin populations? They increase.
How does this illustrate ‘competitive release’? Whales, seals, and penguins
compete for same limited resource; with whales gone, others are released from
competiton and increase in size.
7.
Figure 15. 16.17 Starfish feed on species of herbivores (barnacles, mussels, limpets,
and chitons). Does its presence control diversity of these herbivores?
If…starfish control control competition among herbivores and maintain their
diversity,
then when fish is removed, dominant competitors exclude other species and reduce
species number.
In an experiment in which starfish were removed, the number of herbivore species
rapidly declined from 15 to eight.
How does the result relate to competition? The starfish normally keeps most
dominant competitor at low population size, so other herbivores can persist.
What is a keystone predator? Predator that has a disproportionate effect on species
composition of a community.
HOMEWORK DUE THURSDAY: PROBLEMS 3 AND 4 AT END OF PPT FOR
COMPETITION; USE WORKSHEET ON WEBSITE = ICA 5 COMPETITION
PROBLEMS