Download 14 investigating Population growth rates

14
Investigating Population Growth Rates
T
on the sizes of populations ecosystems can support. These
limits—the carrying capacities for particular populations—are determined
by the resources available and the other species present in the ecosystem. Carrying
capacities of an ecosystem change as the resources in the ecosystem change. The
graph below shows 25 years of population levels of zebra mussels in a lake.
here are limits
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This population of zebra
mussels reached its carrying
capacity around Year 14.
Initially the zebra mussel population grew to a point where the lake could not sustain it, but by Year 14 the population had decreased to a level at which the eco('..H:EJEH<>:Xdad\nH7
system
was able to sustain it over an extended period of time. What factors do you
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think
might change the carrying capacity for this population?
As you learned in the previous activity, many organisms have inter­dependent
­relationships. In predator–prey relationships, the size and health of
one population is frequently closely tied to the size and health of the
other, as you learned in Activity 7, “Energy Flow Through an
Ecosystem.”
A change in a population level is one indicator that can reflect the
health of an ecosystem. A population of a successful invasive species,
such as duckweed, will increase rapidly in a new habitat, possibly
causing the populations of other, native species to shrink. This can
change both population and biodiversity levels. You saw several
examples of this in the first few activities of this unit. The population
growth rate describes the change in a population over specified intervals of time. A positive growth rate indicates that the population is
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zebra mussels.
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Science & Global Issues/Biology • ECOLOGY
growing, while a negative growth rate indicates the population is shrinking.
A population that remains the same size has a zero-growth rate.
In this activity you will examine how different variables affect population growth
rates of a fish population and the carrying capacity of the ecosystem the population lives in.
Challenge
00 How do changing variables alter population growth rates and ecosystem carrying
capacities?
MATERIALS
For each pair of students
computer with Internet access
colored pencils
For each student
Student Sheet 14.1, “Avril Gulf Seal Population”
Student Sheet 14.2, “Investigating Population Growth”
sheet of graph paper
Procedure
1. With your partner, visit the Science and Global Issues page of the SEPUP website at sepuplhs.org/sgi and go to the population simulation. Use your student
sheet to guide you through the simulation.
Analysis
1. Describe the shapes of the graphs you created when working with the online
simulation. Explain what the shape of the curve indicates about the
population.
2. Based on your work in this activity, describe the relationship between birth
and death rates and the growth rate of a population.
3. Based on your work in this activity, describe the relationship between carrying capacity and the size of a population.
4. How do the sizes of populations of other species relate to the sustainability of
the human population? Think of at least two examples, and describe the relationship of each to the human population.
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investigating population growth rates • Activity 14
5. Some bacteria reproduce by doubling once every 20 minutes.
a. If you started with one bacterium, how many would you have in three
hours?
b.Describe what would happen if the bacteria continued to reproduce for 24
hours (do not calculate an exact number).
c. Suggest at least two limiting factors that will ultimately stop the increase of
a bacteria population.
6. Scientists and policy makers often have to work together to set catch limits on
fisheries. Imagine that a policy maker proposes to allow the fishing of a certain species to go on at current rates because, she says, “Fishing at current
rates will not impact the ecosystem. We are removing fish at a rate lower than
the birth rate of their population.” Is this claim valid? What indicators would
you look at to support or disprove this claim? Explain your reasoning.
7. Look at the population graph for the fish population shown below. How
would you describe the growth rate? Is this population sustainable?
8. Examine the data in the Global Human Population graph provided below.
Based on your work in this activity, how would you describe the global
human population growth rate? Explain your reasoning.
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Science & Global Issues/Biology • ECOLOGY
9. Some people claim that the human population has passed its carrying capacity.
What kind of environmental, social, and economic indicators would you
examine to support or argue against this claim?
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Key vocabulary
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carrying capacity
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density-dependent factors
density-independent factors
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