decrease, there is less food for the wolves, so the wolf population also declines. Similarly, as the deer population size increases, so does the wolf population because there is a large food supply.
(e) Answers will vary. Some potential studies include the following:
Sampling to determine the ratio of adults, juveniles, and fry. The following are possibilities:
(i) If fry are most reduced, then the spawning grounds seem to have been disturbed.
(ii) If juveniles are most reduced, then the seals seem to have been too numerous.
(iii) If adults are most reduced, then over-fishing seems to have caused the damage.
Biologist may want to plot the estimated size of harp seal populations and cod populations against time. If cycling occurs, with the cod populations recovering after a certain period, then there is probably no real cause for concern. If cod sizes are below the “normal” cycle level, harp seals may have overhunted the cod, possibly to dangerously low levels. Biologists may also want to look at cod populations away from harp seals. Are the population sizes decreasing there also? If so, there is a possibility that it is something other than the harp seals reducing the population size.
CHAPTER 14 SUMMARY
(Page 692)
Student answers will vary, but students could consider themselves as the organisms. They could refer to the slight decrease in their population from grade 9 to grade 12. They could reflect on examples of mutualism, as they’ve helped each other; commensalism, as they did most of the work in groups, but those who did little received the same mark. They may have run into parasites that did no work at all, only copied others’ reports. Intraspecific competition could include quarrels over girlfriends or boyfriends and their uncertainties about finding placements at universities and colleges next year. Students will realize that they will soon emigrate from high school and immigrate into larger populations. Their abilities are density independent, but first-year placements are density dependant. These types of relationships could be applied to any organism that students choose. Ensure that all major topics covered in the chapter are mentioned in the “day” of the organism.
1. True
2. True
3. False. In nature, species often exhibit clumped dispersal.
4. False. An organism facing interspecific competition always occupies its realized niche.
5. False. Similar species occupying the same niche can reduce competition by resource partitioning.
6. False. Population dynamics of predator–prey interactions show that, in the presence of a predator, prey species often decline but then rebound as predator levels decline in response to the reduced availability of prey.
7. True
8. (d)
9. (c)
10. (e)
11. (b)
12. (a)
13. (c)
14. (e)
15. (c)
(Pages 694–695)
1. Student answers will vary. Students should include an example of a declining population (such as cod) and an increasing population (such as zebra mussels). The cod represent economic loss as the population decreases, and the mussels cause economic loss as their population increases.
Copyright © 2003 Nelson Chapter 14 Population Ecology 311

2. density = population area
=
940
68 ha
=
14/ha
3. (i) random with no visible pattern, such as dandelions on a lawn
(ii) clumped with areas of high and low densities, such as ant hills
(iii) uniform with evenly spaced individuals, such as a cornfield
4. The quadrat method is fast and inexpensive, as it needs to be done only once. It is good for plants and slow-moving small animals. It allows for multispecies sampling and is a good method for finding population sizes over a large area (as long as the total area is known). The mark–recapture method is suited to mobile animals. As it needs to be repeated, it tends to be more expensive, especially since it is best suited to one species at a time. Additionally, several conditions must be met to ensure the accuracy of mark–recapture samples. All organisms must have an equal opportunity of being captured; during the sampling period, the proportion of marked to unmarked individuals must stays constant; and the population size must remain constant. These conditions are rarely met in nature, because organisms are dying, reproducing, emigrating, and immigrating. It is very difficult to keep population sizes constant. Additionally, there is risk to the organism during mark–recapture experiments. The “mark” could cause damage to the organism and even hurt or kill it.
The capturing of the animals is also traumatic. Some people are opposed to this method of sampling because of the potential harm it can cause organisms.
5. Crude density is the ratio of the entire population to the entire habitat area. However, many populations cannot use the entire habitat and are not spread evenly over it. Ecological density is the ratio of the population to the percentage of the habitat that can actually be used. For instance, the crude density of raccoons in Toronto may be 100 per hectare, but once one considers the unusable spaces (for a raccoon), such as bodies of water, the ecological density increases.
6. All habitats provide food resources for a limited number of each type of organism for a limited time. This number is the carrying capacity. This represents the maximum sustainable population for the species. The carrying capacity determines just how large a population can get before resources are used up and the population size crashes. As population size increases, the amount of resources per individual decreases. When populations change density, the new density may exceed the available amount of resources. If a population has high natality or immigration, the population may reach its carrying capacity more quickly. If the death rate or emigration is high, this may reduce the rate at which the carrying capacity is reached.
7. As resources in an ecosystem decline, population size declines as well. If food resources decline, less food is available to the population, so more starvation will occur, increasing the death rate. It may also increase emigration rates as organisms leave the ecosystem to find a new area with more plentiful resources. Similarly, if shelters are rare, many organisms may die or may not be able to reproduce (without available nests), which also decreases population size or slows the growth rate of the population.
8. The Allee effect is a density dependent phenomenon that occurs when a population cannot survive or fails to reproduce enough to offset mortality rates once the population density is too low. Populations like this generally do not survive. The most famous example of an organism that suffered the Allee effect is the passenger pigeon.
9. (a) camouflage
(b) mimicry
(d) camouflage
10. The loss of predators leads to a rapid increase in prey populations. This increase in prey population size can run out of control and can deplete resources for the prey population, causing a population crash and possibly extinction.
11. Similarities
• need living organisms as a food source
• interaction is beneficial to one organism and harmful to another
Differences
• predators kill and consume their prey; parasites are usually harmful but not lethal to the host (if a parasite were lethal,
12. (a) the parasite would likely die also as it depends on the host for food and shelter) population
=
Mn m
=
(175)(135)
=
1125
21
312 Unit 5 Population Dynamics Copyright © 2003 Nelson

(b) The plants may have toxic leaves and bark, which are unpalatable to the deer. They may also have thorns or spurs to detract deer from grazing on them.
13. At low densities, the defence will not be strong enough to protect and shelter the larvae. More larvae will likely be lost, which will then further reduce the population. The population size may get so low that the population cannot recover, which may result in extinction.
14. (a) N. insignis , plot 1 density =
= population area
100 ha
632
+
+
788
100 ha
+
840
+
671
+
100 ha
+
100 ha
=
2931
400 ha
=
7 .
3 /ha
N. insignis , plot 3 density
=
= population area
104 ha
610
+
+
104
559 ha
+
663
+
+
104 ha
601
+
104 ha
=
2433
416 ha
=
5 .
8 /ha
Z. hudsonius , plot 2
= population density
= area
92
345 ha
+
+
9 2
461 ha
+
+
509
9 2
+ ha
328
+
9 2 ha
=
1643
368 ha
= 4 .
5 /ha
Z. hudsonius , plot 3 density
=
= population area
104 ha
102
+
+
104
188 ha
+
+
173
104
+ ha
80
+
104 ha
=
543
416 ha
=
1.3/ha
(b) When the species are found together, in plot 3, they have lower population densities than when found alone. This indicates that they are competing for resources.
(d) Student answers will vary. Some sample answers are below:
It is assumed that there is no migration from other areas into the study plots. This is a difficult assumption to make because with a study area of 100 ha, it is difficult to ensure that no rodents migrate into the area during the study period. The area is so large that there is no way to safely assume that no rodents migrate. no births and deaths during the study period. There is no way that this assumption holds true in the rodent populations over a four-year period.
Copyright © 2003 Nelson Chapter 14 Population Ecology 313

The researchers are also assuming that none of the “marks” is lost over a four-year period. This is also difficult to believe. The rodents may chew tags off, a chip can malfunction, a paint or dye mark can fade, and so on. There is no way to ensure that the proportion of marked to unmarked animals stays constant.
Other assumptions that students may comment on are that food resources are assumed to be identical and that predation is assumed to be absent or negligible.
(e) Quadrat samples of food plants could be included. Tiny transmitters could have been fitted to the rodents. The study site could be reduced in size to try to minimize the chances of migration.
15. (a) Owls: the points show a population that rises and falls over time as measured in years.
(b) Bacteria: in a lab bacteria are provided with ample food resources to support rapid population increases.
16. (a)
Ground Finch Population
600
500
400
300
200
100
0
finch
1990 1991 1992 1993 1994 1995 1996 1997 1998
(b) The carrying capacity is approximately 300 ground finches.
17. (a) The lamprey’s fundamental niche would be a low population density as it is a parasite on large, slowly maturing fish.
The sea lamprey larvae’s fundamental thermal niche is between 17.5ºC and 21.8ºC. They occupy a special niche in stream systems, where they filters microscopic plants and animals from bottom sediments and are prey to several fish and birds. They are borne in fresh water streams, migrate to oceans, return to freshwater to spawn (from July to
October, they enter streams with water at about 10ºC to 15ºC to spawn). Their range is from Baja, California, to the
Bering Sea. They were interred in the Great Lakes in 1920. Their realized niche is now close to their fundamental niche. The period of rapid population increase severely decreased the food resources. Starvation and aggressive predation by humans lowered the lamprey population significantly.
(b) Native to coasts of both sides of the Atlantic; may have entered Great Lakes via Welland canal around 1921.
(c) The lampreys rapidly decreased the population of larger fish, especially lake trout. The removal of the top predator allowed the populations of smaller species of fish to rapidly increase, which depleted their food resources and the caused the crashing of their populations.
(d) Lakes Ontario and Erie had large commercial fishing fleets based in both Canadian and American ports. These have virtually all disappeared, although walleye fisheries have been rebuilt on Lake Erie. Since 1956, the Sea Lamprey
Control Program implemented by the Great Lakes Fishery Commission (with U.S. and Canadian cooperation) has been successful. However, the present focus is on reducing the use of lampricide through alternative control methods, such as the construction of barriers in streams to deny them entry and experimental programs to decrease spawning by sterilizing male sea lampreys; these have so far been successful in allowing the reemergence of many fresh water fishes.
Helpful Websites: http://www.great-lakes.org/exotics.html http://www.psmfc.org/habitat/edu_lamprey_fact.html http://anstaskforce.gov/moreimpacts.htm http://www.meer.org/index.htm
314 Unit 5 Population Dynamics Copyright © 2003 Nelson

18. Student answers will vary depending on their research. Tagging and releasing organisms; Monarch butterflies. Fred
Urquhart was the first to tag a monarch butterfly (1937); he determined their migration pattern in 1975. Butterflies were netted and small tags were carefully pressed onto the leading edges of their wings.
Copyright © 2003 Nelson Chapter 14 Population Ecology 315