Download Population Growth Modeling Study

SIDNEY PUBLIC SCHOOLS
Population Growth Modeling Study
How does the Impact of Competing Species
Affect the Maximum Population of Competitors?
SAMPLE
5/14/2014
Investigation Question
If the impact of a competing species in a given environment is increased, what happens to the maximum
population of the competitor?
Background Research
Ecologists study populations to know how and why populations change over time (N.A.
Campbell, pg. 726). They are interested in the causes of population change, limits of population growth,
the affects that the environment and other organisms in it have on the population of a particular
species. Knowing how and why a population is changing can help scientists manage and maintain the
integrity of a population whether it be a population of domesticated farm animals, predators affecting
other populations in the wild, or pest species that occupy, destroy or otherwise interfere with habitat
that might otherwise by occupied by more important species or species more beneficial to humans.
In this modeled study, I will be considering how the impact of one species affects a competitor
in the same environment. Impact of a species can include various aspects of the organisms considered
including size. For example, if you considered grazing animals in grassland environments, American
buffalo feed on many of the same grasses and plant life that the cottontail rabbit consumes. Individually
and as a population, the bison would have a bigger impact based on its size and the amount of food it
consumes. Another example of impact might include the lifespan of organisms. A short life-span will
mean that even though an species of organisms may be larger or consume more than a competing
species, the species may have a lower impact on a given environment than its competing species with a
longer life span.
Some of the ways in which I will use the population growth spreadsheet model (Vernier, exp. 18,
Modeling Population Growth) to reveal information about how changing the impact of one species
affects another can involve the following:
1. monitoring changes in the maximum population of competitor (herbivore) 2 when the impact of
competitor (herbivore) 1 is increased.
2. monitoring the number of generations it takes for a competitor (herbivore) 2 to reach the population
carrying capacity.
3. comparing the difference in maximum populations reached by the competing organisms. For
example, when the impact of competitor (herbivore) 1 is increased by impact increments of .10, how
does the maximum population of herbivore 1 compare with the maximum population of herbivore 2?
What are the differences in maximum populations of the competitors as the impact of the one
competitor is increased?
Carrying capacity is the maximum population of a particular species that a given environment can
support. This does not always mean that a population will reach the carrying capacity population of the
environment. Competition, predators, disease and other factors can affect the actual number of
individuals in a population. This includes the impact factors considered in this model. The investigation
is intended to look at how the impact of one competing species can affect the ability of another
competing species population to grow and approach its carrying capacity.
Hypothesis
Null hypothesis – Increasing the impact of a competing species will not affect the maximum population
of another competitor species in the environment.
Alternate hypothesis – Increasing the impact of a competing species will reduce the ability of another
competing species population to grow to its environmental carrying capacity.
Materials
computer, population growth model spreadsheet (Vernier Software and Technology), references
(ecology chapters in Biology Text, others as provided – see references/works cited).
Variables:
Manipulated (independent) – impact of competing species (herbivore 2)
Responding (dependent) – population changes of competitor (herbivore 1)
Controlled variables (unchanged) – predation, kill rate, death rate, growth rate
Procedure
1.
Open the population growth modeling spreadsheet provided for the exercise.
2. Use the competition tab to investigate the effect of a competing organism’s impact on the
population of a species that it is competing with. Change the impact of the competitor
(herbivore 2) from .10 to .70 in .2 increments (ie-.10, .30, .50, .70). If there is no observable
changes, try different increments and increment ranges; for example, a range of .20 to .40 in
impact increments of .05
3. Print the default settings graph (impact = .10) for a baseline with which to compare the results
of other impact levels of one competing species (Herbivore 2) on the population of the
competing species (Herbivore 1).
4. Print graphs or data tables for each of the impact settings. (I will test impact settings of .1 to .7).
5. Use graphs to compare to the default. Construct a simple data table comparing the results that
you developed.
Results
View graphs to compare changes in impact vs. population with respect to carrying capacity of competing
species.
Data Table:
Impact of
Maximum Population
% of carrying
Herbivore 2
of Herbivore 1
capacity reached by
Herbivore 1
.1
977
97.7
.3
934
93.4
.5
892
89.2
.7
849
84.9
Summary of Results
The results show that increasing the impact of a competing species decreases the ability of
another competitor to reach its carrying capacity. For the tested range of impacts of the competing
organism (H2), the maximum population of the other competing species (H1) is decrease steadily about
42 or 43 individuals of species (H1) for each impact increase of .2 for the competing H2 species. This
graph of the changes in impact of H2 and the maximum population shows this inverse relationship. The
linear relationship show a slope of about -21.2 individuals of H1 per .1 increase in impact of species H2.
The model graphs of the overall population of each competitor also indicates that as the impact
of the competing species H2 increases, the stable population of that species continues to increase and
close in on its carrying capacity. Meanwhile, the original species (H1) has a stable population that is also
decreasing.
Conclusion
The effect of competitor impact agreed with the hypothesis as stated. Increasing competitor
impact does decrease the maximum population of other competing species according to the results of
this model. These results do not agree with the null hypothesis that competitor impact has no effect on
the maximum that a competing population will reach. Further investigations could consider some of the
following ideas.
1.
How does the impact level of one species in an environment affect the stable population
levels of competing species?
2. How does the carrying capacity of one species impact maximum and/or stable population
levels of a competing species?
References
Campbell, N. A. (2009). Biology: Concepts and Connections. San Fransisco: Pearson Education , Inc.
Melville, J. M. (2012). Investigating Biology through Inquiry. Beaverton, OR: Vernier Software and
Technology. Experiment 18 - Modeling Population Dynamics
Greenwood, Tracy and others. (2012). AP Biology 2 Student Workbook. Hamilton, New Zealand:
Biozone International Ltd.