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CHAPTER 20
UNIT D PROJECT:
What Limits the
Growth of Grizzly Bear Populations?
Purpose: Recognizing the intrinsic factors that limit grizzly bear population growth.
Number of Grizzly
Procedure
Bears in Alberta,
Using the data in the first table, draw a graph that shows the change in size of Outside the National
the Alberta grizzly bear population outside the National Parks over time. ThenParks
complete the following Analysis questions.
Population
Year
Analysis
size
1988
575
For your graph, label the growth curve with the following labels: lag,
1989
536
growth, stationary, death. (D3: label and describe the phases of a
1990
547
growth curve of a population)
1991
638
1992
669
1993
686
1.
1994
700
1995
735
A. The number of grizzly bear deaths in Alberta from 1976 to 1988 was
1996
765
estimated to be 581. Only 281 births were recorded from 1976 to 1988.
1997
776
33 grizzly bears from the west immigrated to the area, yet, 25 bears
1998
807
emigrated. How does this information affect the population size? What
1999
833
would the growth rate be for the areas outside of the National Park? (D3:
2000
841
explain how mortality and natality influence population growth, growth
rate)
B. Using the information provided, how would the immigration of the Alaskan black bear affect the
gene pool of the Grizzly bear. (D1: affects of gene pool change)
Black bears are most easily distinguished from brown bears by their straight
facial profile and their claws which are sharply curved and seldom over 1½
inches in length. Positive identification can be made by measuring the upper
rear molar which is never more than 1¼ inches long in the black bear and is
never less than that in a brown bear. Black bears have adequate senses of
sight and hearing. They do have, however, an outstanding sense of smell.
Source: Alberta Wildlife Status
Reports, Alberta Sustainable
Resource Development, 2002
C.Identify the factor that would influence the gene pool. (D1:
Describe the factors that cause the gene pool to change)
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CHAPTER 20
HANDOUT
Thought Lab 20.2: What Limits the
BLM 20.1.8
Growth of Grizzly Bear Populations?
(cont’d)
D. In a population of the Alaskan Black bear, there was a 3 in 2000 of bears that exhibit a white fur.
Identify the dominant and recessive alleles in the population. Then, give the amount of bears that
would carry the allele for white fur.
2.
Using the Population Size table on the previous page, determine the per capita growth rate
(cgr) for each of the following time intervals: 1991 to 1992, 1997 to 1998, and 1998 to 1999.
Suggest why the cgr has changed over time. (D3: determine per capita growth rate of a
population)
3.
Population counts were made in several bear management regions around the province. Some
of the data are shown in following table.
Grizzly Bear Population Sizes in Alberta
Region
Area (km2)
Bear population
A
14 128
31
B
6 089
44
C
22 840
168
Source: Alberta Wildlife Status Reports, Alberta Sustainable Resource
Development, 2002
a) For each region, determine the number of grizzly bears per 1000 km2. (D3: determine
population density.)
CHAPTER 20
HANDOUT
Thought Lab 20.2: What Limits the
BLM 20.1.8
Growth of Grizzly Bear Populations?
(cont’d)
b) Compare the densities for the three regions. Suggest three reasons for the differences, if any.
Explain your thinking.
4.
5.
Define carrying capacity. Very few grizzly bears die of old age. What are two other possible
causes of death, not associated with human activities, using the term carrying capacity in your
answer? (D3: define carrying capacity and environmental resistance and describe their effect
on the growth of a population)
Environmental resistance involves those factors in an environment such as predators,
competition, climate, and food availability, that would affect population growth. Describe at
least two methods of resistance to the bears’ population growth over time. (D3: define
environmental resistance and its effect on the growth of a population).
CHAPTER 20
HANDOUT
Thought Lab 20.2: What Limits the
BLM 20.1.8
Growth of Grizzly Bear Populations?
(cont’d)
6.
Studies have shown that male grizzly bears will cross roads and use underpasses to forage in a
better environment. Females tend to remain in more restricted areas.
How might the movement of male and female grizzly bears in their habitat affect genetic diversity in
the population? (D1: recognize causes of gene pool changes)
7. Grizzly bears reach sexual maturity at five years of age. When food is abundant, females average
two cubs per litter every other year. With inadequate nutrition, females produce fewer cubs.
(D3:characteristics and reproductive life strategies)
a. Compared with mosquitoes, how would you describe the life strategy of grizzly bears?
b. Define biotic potential. Explain why the biotic potential of grizzly bears is relatively low.
(D3:identify biotic potential characteristics)
CHAPTER 20
HANDOUT
Thought Lab 20.2: What Limits the
BLM 20.1.8
Growth of Grizzly Bear Populations?
(cont’d)
8.
a. Mosquitos’ method of survival is drastically different than a bears’ survival. Identify and
explain the symbiotic relationships that mosquitos have to bears and bears to mosquitos.
(D2: describe symbiotic relationships)
b. An infestation of mountain pine beetle has caused trees to be affected in the Banff National
Park. As well, the adult mountain pine beetles emerge from an infested tree over the course of
the summer and into early fall. The mountain pine beetle transmits a fungus that stains a tree's
sapwood blue. Bears will exhibit a tendency to use trees to get rid of an itch they can’t scratch.
How would this affect the bear population? (D3: identify an environmental resistance; D1 affects
on gene pool)
c. Identify the mountain pine beetles’ symbiotic relationship with the tree. Explain how this
relationship works. (D2: describe and identify symbiotic relationships)