Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN: 9780134580999
Author: Elaine N. Marieb, Katja N. Hoehn
Publisher: PEARSON
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Carrying Capacity and the Bison of Yellowstone National Park
The following text is adapted from an article in Yellowstone Science, a journal published by the National Park Service.
An important part of the Yellowstone National Park ecosystem, bison are the largest land mammals in North America. Yellowstone bison historically occupied approximately 7,720 square miles (20,000 km²) in the headwaters of
the Yellowstone and Madison rivers. Today, this range is restricted to primarily Yellowstone National Park and some adjacent areas of Montana. The bison population is subdivided into the central and northern breeding herds.
One of the key issues related to the Yellowstone bison population is how it should be managed. From the beginning of the twentieth century through 1966, bison numbers were kept in check through regular culling. This culling
was stopped in 1969. Officials decided to allow bison numbers to fluctuate according to such factors as weather, the availability of resources, and predators. The result was a dramatic increase in the numbers of Yellowstone bison.
Figure 1 shows population numbers for the central and northern herds for 1970-2010.
1
2
3
4
5
6
Number of Bison
4000
3500
3000
2500
2000-
1500.
1000
500.
0
1970
* Central Herd
Northern Herd
Hunting
Culling
Bison
Distribution
1980
Weather
As the number of Yellowstone bison increased, more bison began migrating to areas outside of the Yellowstone Park boundaries during the winter months. In the 1940s, Yellowstone bison were concentrated in two main areas
comprising a relatively small portion of the park. By 2007, the range of Yellowstone bison was greatly expanded. Bison were found throughout Yellowstone Park and even beyond its boundaries.
Bison are migratory. They move to lower elevation ranges during the winter months in response to snow accumulation and snowpack development. They also change their diets slightly during the winter, preferring to feed in
lowland meadows where the growth of sedges and grasses is concentrated. The movement of the bison beyond park boundaries, however, raised questions about whether their numbers were too high and if the forage inside the
park was inadequate to support the bison population.
Fire
1990
Year
In 2011, Dr. P. J. White and others published a review paper addressing the question of whether Yellowstone bison were moving outside of the park because they had exceeded their carrying capacity (White et al., 2011). As a
population increases in size, the finite amount of water, food, and shelter in an area must sustain and support a larger number of individuals. Eventually, numbers may increase to the point where this is no longer possible. At this
point, the carrying capacity has been exceeded. One study the researchers referenced was an earlier study by one of the study's coauthors (Coughenour, 2005). This study used an ecosystem model to evaluate whether bison had
exceeded their carrying capacity inside Yellowstone National Park. The study focused on food availability as the limiting factor. The model developed was named the SAVANNA model. The model integrates data from several
ecosystem-related variables, including predator populations, the production of plant biomass, physical land features, and water availability. Figure 2 shows a simplified version of the model and some of the interrelated variables
used in the model. For example, hunting and culling as well as predation can reduce the size of the bison population. The SAVANNA model also uses weather data from various sites within the park to simulate winter snow
accumulation as well as snow melt.
Predation
Bison
Population
2000
Plant
Population
Soils
2010
Figure 1 - Data for bison observed during
aerial surveys conducted between July 1970
and August 2010. Source: NPS
Plant
Consumption
Water
Budget
Figure 2 - Selected essential components of the
SAVANNA ecosystem model. Modified from White
et al. (2011)
The model simulates the populations of the two main bison breeding herds in Yellowstone National Park as well as nine plant groups. Eight simulations spanning a period of 50 years were completed using the model to determine
whether Yellowstone bison had exceeded their food-limited carrying capacity inside the park. The simulations did not allow Yellowstone bison to expand their range beyond the park boundaries. The simulations predicted the sizes of
the two main herds by estimating the mean size of each herd, the median size of each herd, and the possible range in the size of each herd. These data were then compared to actual 2005 population data for Yellowstone bison.
The results of the simulations and the 2005 bison population numbers are shown in figure 3.
The following question has two parts. First, answer Part A. Then, answer Part B.
Part A:
Which statement is a valid analysis about bison movement and the carrying capacity of Yellowstone National Park?
O
A. The decrease in the northern herd's population is explained by its inability to migrate and the park's decreasing carrying capacity.
O
O
O
B.
O
C.
D.
O
Part B:
Which selection from the text provides evidence that directly supports this analysis?
The fact that bison only migrate in years of deep snow indicates that they have exceeded the park's carrying capacity.
O
A. They move to lower elevation ranges during the winter months in response to snow accumulation and snowpack development.
B.
The carrying capacity for other animals found in Yellowstone has increased due to the bison's migration outside of the park.
The movement of bison beyond park boundaries is not due to the bison population being too large for the park's carrying capacity.
D.
O
C. The actual population of the northern herd in 2005 was significantly smaller than the smallest population predicted using the model, as well as smaller than the median and mean predictions.
The model integrates data from several ecosystem-related variables, including predator populations, the production of plant biomass, physical land features, and water availability.
Scientists have suggested several possible explanations for the movement of Yellowstone bison outside of the park even though they have not exceeded their food-limited carrying capacity.
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Transcribed Image Text:Carrying Capacity and the Bison of Yellowstone National Park The following text is adapted from an article in Yellowstone Science, a journal published by the National Park Service. An important part of the Yellowstone National Park ecosystem, bison are the largest land mammals in North America. Yellowstone bison historically occupied approximately 7,720 square miles (20,000 km²) in the headwaters of the Yellowstone and Madison rivers. Today, this range is restricted to primarily Yellowstone National Park and some adjacent areas of Montana. The bison population is subdivided into the central and northern breeding herds. One of the key issues related to the Yellowstone bison population is how it should be managed. From the beginning of the twentieth century through 1966, bison numbers were kept in check through regular culling. This culling was stopped in 1969. Officials decided to allow bison numbers to fluctuate according to such factors as weather, the availability of resources, and predators. The result was a dramatic increase in the numbers of Yellowstone bison. Figure 1 shows population numbers for the central and northern herds for 1970-2010. 1 2 3 4 5 6 Number of Bison 4000 3500 3000 2500 2000- 1500. 1000 500. 0 1970 * Central Herd Northern Herd Hunting Culling Bison Distribution 1980 Weather As the number of Yellowstone bison increased, more bison began migrating to areas outside of the Yellowstone Park boundaries during the winter months. In the 1940s, Yellowstone bison were concentrated in two main areas comprising a relatively small portion of the park. By 2007, the range of Yellowstone bison was greatly expanded. Bison were found throughout Yellowstone Park and even beyond its boundaries. Bison are migratory. They move to lower elevation ranges during the winter months in response to snow accumulation and snowpack development. They also change their diets slightly during the winter, preferring to feed in lowland meadows where the growth of sedges and grasses is concentrated. The movement of the bison beyond park boundaries, however, raised questions about whether their numbers were too high and if the forage inside the park was inadequate to support the bison population. Fire 1990 Year In 2011, Dr. P. J. White and others published a review paper addressing the question of whether Yellowstone bison were moving outside of the park because they had exceeded their carrying capacity (White et al., 2011). As a population increases in size, the finite amount of water, food, and shelter in an area must sustain and support a larger number of individuals. Eventually, numbers may increase to the point where this is no longer possible. At this point, the carrying capacity has been exceeded. One study the researchers referenced was an earlier study by one of the study's coauthors (Coughenour, 2005). This study used an ecosystem model to evaluate whether bison had exceeded their carrying capacity inside Yellowstone National Park. The study focused on food availability as the limiting factor. The model developed was named the SAVANNA model. The model integrates data from several ecosystem-related variables, including predator populations, the production of plant biomass, physical land features, and water availability. Figure 2 shows a simplified version of the model and some of the interrelated variables used in the model. For example, hunting and culling as well as predation can reduce the size of the bison population. The SAVANNA model also uses weather data from various sites within the park to simulate winter snow accumulation as well as snow melt. Predation Bison Population 2000 Plant Population Soils 2010 Figure 1 - Data for bison observed during aerial surveys conducted between July 1970 and August 2010. Source: NPS Plant Consumption Water Budget Figure 2 - Selected essential components of the SAVANNA ecosystem model. Modified from White et al. (2011) The model simulates the populations of the two main bison breeding herds in Yellowstone National Park as well as nine plant groups. Eight simulations spanning a period of 50 years were completed using the model to determine whether Yellowstone bison had exceeded their food-limited carrying capacity inside the park. The simulations did not allow Yellowstone bison to expand their range beyond the park boundaries. The simulations predicted the sizes of the two main herds by estimating the mean size of each herd, the median size of each herd, and the possible range in the size of each herd. These data were then compared to actual 2005 population data for Yellowstone bison. The results of the simulations and the 2005 bison population numbers are shown in figure 3. The following question has two parts. First, answer Part A. Then, answer Part B. Part A: Which statement is a valid analysis about bison movement and the carrying capacity of Yellowstone National Park? O A. The decrease in the northern herd's population is explained by its inability to migrate and the park's decreasing carrying capacity. O O O B. O C. D. O Part B: Which selection from the text provides evidence that directly supports this analysis? The fact that bison only migrate in years of deep snow indicates that they have exceeded the park's carrying capacity. O A. They move to lower elevation ranges during the winter months in response to snow accumulation and snowpack development. B. The carrying capacity for other animals found in Yellowstone has increased due to the bison's migration outside of the park. The movement of bison beyond park boundaries is not due to the bison population being too large for the park's carrying capacity. D. O C. The actual population of the northern herd in 2005 was significantly smaller than the smallest population predicted using the model, as well as smaller than the median and mean predictions. The model integrates data from several ecosystem-related variables, including predator populations, the production of plant biomass, physical land features, and water availability. Scientists have suggested several possible explanations for the movement of Yellowstone bison outside of the park even though they have not exceeded their food-limited carrying capacity.
7
8
9
Number of Bison
6000
5000
4000+ Range
1820-3530
3000+
2000
1000+
Median
Mean 2670
2417
Simulation
Results
Range
2430-5630
Median
Mean 4030
3531
3776
+₁1
1484
Simulation
Results
2005
Population
(Northern Herd) (Central Herd) (Northern Herd) (Central Herd)
2005
Population
Figure 3 Simulation results and 2005 bison
population data. Data from White et al. (2011)
As shown, the simulated bison population was larger than the actual population in 2005. The actual population of the northern herd in 2005 was significantly smaller than the smallest population predicted using the model, as well
as smaller than the median and mean predictions. The smallest population size for the central herd predicted using the model was lower than the actual size of the central herd in 2005. However, the mean, median, and maximum
predicted size of the central herd population were all significantly greater than the actual size of the central herd in 2005. These results suggest that actual bison numbers could have increased by approximately 200 to 2000 before
the herd would have been in danger of exhausting its food supply. Food availability was the limiting factor in the SAVANNA model, so if actual bison numbers had been higher than those predicted by the model, it would suggest that
Yellowstone bison had exceeded their food-limited carrying capacity inside the park. However, this was not the case. This led the researchers to conclude that the food-limited carrying capacity for the Yellowstone bison had not
been reached.
However, the model also suggested that carrying capacity could vary from year to year due to other factors aside from food availability, including weather and competition for resources. Additionally, winter weather conditions
resulting in deep snowpacks could limit the ability of Yellowstone bison to access food. Figure 2 shows that the model allows for the fact that weather can affect plant consumption. If snow is extremely deep, bison may have trouble
accessing the plants they need to survive. If they cannot obtain adequate nutrition during part of the year, the bison population may decrease due to this temporary food shortage. Therefore, bison deaths due to starvation could
occur even when bison numbers are well below the food-limited carrying capacity.
Scientists have suggested several possible explanations for the movement of Yellowstone bison outside of the park even though they have not exceeded their food-limited carrying capacity. Variations in the local climate are one
possible factor. Areas outside of the park where snow melts sooner because the elevation is lower would provide better foraging opportunities. The bison may also simply be expanding their range to reduce population density (the
number of individuals in a specific area) and therefore lessen the competition for an area's resources. This reduced competition and greater resource availability could have a positive effect on the Yellowstone bison's nutrition,
reproduction, and survival.
References:
Coughenour, M. B. 2005. Spatial-dynamic modeling of bison carrying capacity in the Greater Yellowstone ecosystem: A synthesis of bison movements, population dynamics, and interactions with vegetation. Natural Resource
Ecology Laboratory, Colorado State University, Fort Collins, Colorado.
White, P., Plumb, G., Coughenour, M, and Wallen, R. "Carrying Capacity and Movements of Yellowstone Bison." Yellowstone Science 19.1 (2011). Web. 5. May. 2014 [Available from:
http://www.nps.gov/yell/planyourvisit/upload/YS_19_1_sm.pdf]
expand button
Transcribed Image Text:7 8 9 Number of Bison 6000 5000 4000+ Range 1820-3530 3000+ 2000 1000+ Median Mean 2670 2417 Simulation Results Range 2430-5630 Median Mean 4030 3531 3776 +₁1 1484 Simulation Results 2005 Population (Northern Herd) (Central Herd) (Northern Herd) (Central Herd) 2005 Population Figure 3 Simulation results and 2005 bison population data. Data from White et al. (2011) As shown, the simulated bison population was larger than the actual population in 2005. The actual population of the northern herd in 2005 was significantly smaller than the smallest population predicted using the model, as well as smaller than the median and mean predictions. The smallest population size for the central herd predicted using the model was lower than the actual size of the central herd in 2005. However, the mean, median, and maximum predicted size of the central herd population were all significantly greater than the actual size of the central herd in 2005. These results suggest that actual bison numbers could have increased by approximately 200 to 2000 before the herd would have been in danger of exhausting its food supply. Food availability was the limiting factor in the SAVANNA model, so if actual bison numbers had been higher than those predicted by the model, it would suggest that Yellowstone bison had exceeded their food-limited carrying capacity inside the park. However, this was not the case. This led the researchers to conclude that the food-limited carrying capacity for the Yellowstone bison had not been reached. However, the model also suggested that carrying capacity could vary from year to year due to other factors aside from food availability, including weather and competition for resources. Additionally, winter weather conditions resulting in deep snowpacks could limit the ability of Yellowstone bison to access food. Figure 2 shows that the model allows for the fact that weather can affect plant consumption. If snow is extremely deep, bison may have trouble accessing the plants they need to survive. If they cannot obtain adequate nutrition during part of the year, the bison population may decrease due to this temporary food shortage. Therefore, bison deaths due to starvation could occur even when bison numbers are well below the food-limited carrying capacity. Scientists have suggested several possible explanations for the movement of Yellowstone bison outside of the park even though they have not exceeded their food-limited carrying capacity. Variations in the local climate are one possible factor. Areas outside of the park where snow melts sooner because the elevation is lower would provide better foraging opportunities. The bison may also simply be expanding their range to reduce population density (the number of individuals in a specific area) and therefore lessen the competition for an area's resources. This reduced competition and greater resource availability could have a positive effect on the Yellowstone bison's nutrition, reproduction, and survival. References: Coughenour, M. B. 2005. Spatial-dynamic modeling of bison carrying capacity in the Greater Yellowstone ecosystem: A synthesis of bison movements, population dynamics, and interactions with vegetation. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado. White, P., Plumb, G., Coughenour, M, and Wallen, R. "Carrying Capacity and Movements of Yellowstone Bison." Yellowstone Science 19.1 (2011). Web. 5. May. 2014 [Available from: http://www.nps.gov/yell/planyourvisit/upload/YS_19_1_sm.pdf]
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