Biology 12

Chapter 14 Population Ecology • MHR 491

density does play a role. The amount by which N
exceeds the number of hiding places will affect the
proportion of the population killed. In fact, most
populations are probably regulated by a
combination of density-dependent and density-
independent factors.

The abiotic and biotic factors that regulate

population size also influence other characteristics

of populations. These characteristics will be

described in the last section of this chapter.

SECTION REVIEW

1. What factors might eventually limit the
   exponential growth rates of a particular insect species
   found in such regions as the Canadian prairies?


2. What might allow some animal populations to
   grow beyond the theoretical carrying capacity of their
   environment and then crash to abnormally low levels?


3. What factors might limit the population size of
   animals (such as vultures) that live as scavengers?


4. In a density-dependent population, why does
   population growth decline as population density
   increases?


5. Provide a real-life example of a situation in which
   interspecific competition limits the population size
   and growth of a particular species.


6. What combination of factors might produce
   regular population cycles typical of small herbivore
   species such as mice and squirrels?


7. Rat populations in many urban areas in Canada
   have increased dramatically in recent years. Use the
   Internet to research public health records and other
   web sites for data about the extent of this problem.
   Describe the factors that seem to be contributing to
   the growth in local rat populations and the factors
   that may ultimately limit their population size.


8. Biologists have observed increasing instances
   of coral bleaching in recent years. This phenomenon
   involves the death of small green algae that live in the
   tissues of coral polyps (the tiny animals whose bodies
   secrete much of the material that forms coral reefs).
   Following the death of the algae, the coral organisms
   that hosted them also die. Describe the probable
   type of relationship that exists between the algae
   and coral organisms.


9. Some species of sharks are often seen with
   small fish called remoras attached to their bellies. The
   remoras seem to feed off the scraps of food dropped
   by the sharks when they are feeding on prey. The
   sharks seem to derive no benefit from the presence
   of the remoras. What type of symbiotic relationship
   might the association of the shark and remora
   illustrate? Do you think it likely that the shark is totally
   unaffected by the remora? In what way might it be

affected? In what way might your answer to this last

question change your interpretation of the type of

relationship exhibited here?

10. What is the difference between the way in
    which abiotic and biotic factors typically produce
    environmental resistance to population growth?


11. Roosevelt elk (Cervus elaphus roosevelti) were
    re-introduced to the Sunshine Coast region of British
    Columbia because overhunting eliminated the original
    elk population many years ago. Their population has
    now grown to about 250, and some local residents
    are complaining that the elk are devouring plants in
    gardens, parks, and golf courses. Limited hunting of
    this population is now permitted in an attempt to
    control the problem. Do you think hunting of this elk
    population should be permitted? How do you think
    the resumption of hunting might affect the long-term
    growth patterns of this population and other species
    that share the same environment as the elk?


12. In ecological terms, what measures would be
    most effective in controlling populations of pest
    species such as rats, mice, or certain types of insects?


13. Having been recently appointed regional wildlife
    manager, you must set a quota on the number of
    moose that can be hunted during the next hunting
    season. What information do you need? Design a
    study that will allow you to obtain the necessary data.


14. You have just been hired to teach Grade 6 at
    a local school. Design a lesson plan, including an
    activity, that you might use to teach your students
    about the factors that affect population growth in
    different environments.


15. Although all populations eventually face
    environmental resistance to continued growth, the
    contribution of abiotic and biotic factors to this
    resistance may vary from species to species.
    Compare a micro-organism, such as E. coli, a plant
    (such as a type of tree), and a mammal, such as the
    snowshoe hare or the black bear, with respect to the
    type of factors that typically limit the growth of
    populations of each species.

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