ICA 4 COMPETITION
Group Name _______________ Your name _______________
PART 1
1. What is facilitation? one species aiding another species
Why would a species AID another species? Is it costly? It is of no cost to the species
aiding the other. If it cost the species, it would not survive (compete) as well as the
species it is aiding.
2. Define competition. use or defense of a limiting resources that reduces availability to
others.
Define a superior competitor: It can persist at lower resource levels than inferior
competitors.
3. What’s the difference between exploitation = a species (or individual) grabs
resources independent of what the other species (individual) is doing
vs. interference = a species actively defend resources and interfere directly with the
other species from gaining the resource competition?
Intra- between individuals of same species vs. inter- between 2 species -specific
competition.
4. Allelopathy: allelo= other pathy causing sickness
How does it work? A species exudes chemicals that interferes with another species
metabolism/performance and limit the second species access to a resource.
5. Plants compete for what resources? nutrients, light, water, pollinators, microbes, seed
dispersers
Animals compete for what resources? food, territory (space), hiding places
6. Does a resource have to be limited for competition to arise? Explain Yes. If they were
unlimited each individual (species) would have plenty of resources and not suffer if
the other individuals (species) has some resources in the area.
What’s a renewable resource? constantly regenerated e.g. prey, nutrients
What’s a non-renewable resource? can be fully re-used e.g. space, hiding places
7. What is Liebig’s Law of the Minimum? Populations are limited by the single resource
that is most scare.
How does it affect population growth? Population increases until limiting resource
becomes insufficient, and then, growth stops.
Fig. A.Why is it considered ‘simplistic’? Resources don’t act in isolation of other
resources. One resource affects how other resources can be used. Fig. B.What is
meant by synergism? When two factors work together, often resulting in more than the
sum of what the two do individually.
8. Figure C. What is the Law of Constant Yield? After a population exceeds some
limiting resource, addition of further individuals does not result in a greater
population; no more yield is possible after a certain density.
9. How does intraspecific competition relate to density-dependent regulation of
population growth? Such competition increases with density and serves to dampen
population growth.
What are 4 negative density-dependent growth responses? slower growth; longer time
to reach sexual maturity, lower birth rate; higher death rate
10. 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. 4. Proportion of females with offspring decreases with increasing population
size.
Fig. 5. Birth rate decreases and death rate increases with increasing population.
When B = D, the population size stabilizes.
What does the dark circle represent on the two lines? B = D
What does the dark circle on the X-axis represent? Population size at which
no further growth occurs (equilibrium population size).
11. What is the formula for logistic growth? dN/dt = rN (K-N)/K
Which component represents intraspecific competition? N of (K-N)/K
What is the consequence for population growth? The closer N becomes to K, the
more the population growth is slowed down.
Express the effect of population size on r: r decreases with increasing pop. size.
At what value of r does N = K? When r = 0, N = K.
12. What is the effect of interspecific competition on r? no effect; on K? It lowers K.
Fig. 6. 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
13. How is interspecific competition added to the logistic equation? by subtracting from
K of species 1 because some of the resources are being used by species 2.
How does its addition affect dN/dt? It lowers it (it lowers it more the closer the the
higher the value of 1,2 and N of species 2 ).
What is the competition coefficient 1,2 = effect of each individual of sp 2 on sp 1
What is the competition coefficient 1,2 = effect of each individual of sp 1 on sp 2
Figure 7. What is the value of 1,2? = 4
PART 2
1. Operationally, what is a niche? ranges of conditions and resource qualities within
which species persists.
What is meant by a hypervolume of niche space? multiple resource axis describe
niche space; more axes  hypervolume
2. What is niche breadth in relation to a resource axis? range of resources in which
species persists.
What is niche overlap? part of resource (niche) axis shared by 2 species.
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
What is the difference between fundamental = range of resource axis used with no
competitors; realized = reduced range of resource axis used when competitors
present niche? Which is smaller? realized niche
3. Figure 8. B. What do the different contour lines represent? abundance of the bird at
2 particular resource levels. Under what conditions is the bird most abundant? Prey
length of 4 and foraging at 4 m above ground Does Figure 8B show the fundamental
or realized niche of the bird? probably realized
Figure 8 A. Are fundamental or realized niches shown? fundamental What
will be the realized niche of species A? Can’t tell On what does it depend? Whether
sp A or sp B is the better competitor.
4. 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.
5. 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. 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. 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. Under what conditions can two species coexist? Two species can coexist
if they are limited by different resources.
Fig. 13. What is the main conclusion of this experiment? The outcome of competition
between these two insects depends on temperature.
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. What is meant by ‘apparent competition’? Predators feeding on superior competitor
alter competiting species rather than competitors altering competitors.
Figure 15. 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.
8. Figure 16. Describe the main pattern in A. As number of newts increase, relative
weight of three prey changes in B. Which species of amphibian is most competitive
in the absence of the newt? Scaphiopus in the presence of 8 newts per pond? Hyla
What is the ‘take-home’ message
about predators and competition? . Outcome of competition among prey changes in
presence of a predator.
HOMEWORK DUE THURSDAY: PROBLEMS 4 AND 5 AT END OF PPT FOR
COMPETITION; USE WORKSHEET ON WEBSITE = ICA 5 COMPETITION
PROBLEMS