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As you learned in Chapter 1, ecosystems are a complex and delicate balancing game. The addition or removal of any species affects many other species that might compete for or provide food. These interspecific interactions are further influenced by human impacts on the environment such as habitat fragmentation. Chapter 4 noted how disturbances associated with deforestation and urban sprawl alter environmental conditions in ways that can both shift competitive outcomes in ecosystems and threaten human well-being.
In this lab you will apply the scientific method to examine how thresholds of land use changes such as deforestation and urban sprawl can impact communities, predator/prey relationships, species diversity, and quality of life in human communities.
The imaginary forest town of Pinchot, California is facing a land use planning battle. Conservationists and the local outdoor recreation industry want to protect at least 75% of Pinchot’s surrounding forest reserve to maintain the town’s natural heritage, including its unique biodiversity and valuable ecosystem services. Developers, however, want to expand the town’s neighborhoods and shopping malls and insist that protecting 25% of the reserve is all that is needed to sustain the forest’s biodiversity and economic value.
You have been appointed to a select team of scientists tasked with using the scientific method to evaluate the impacts of fragmentation on the forest reserve and community. Your objective is to determine the percent of intact forest that must be maintained to protect the reserve’s biodiversity and ecosystem services.
To achieve this objective, your team has developed a computer model based on decades of plant and animal population data collected by the Dept of Fish & Wildlife and local land trusts. Your modeling has also incorporated population data from the forest reserves of three nearby towns, which are 25%, 50% and 75% fragmented, respectively.
By comparing how fragmentation has impacted four ecologically important species within these four forest reserves, your team aims to answer the question of whether 25%, 50% or 75% fragmentation will be “sustainable” for Pinchot’s forest in terms of sustaining its biodiversity and ecosystem services. The science-based hypothesis that you are testing, using this computer model, is that neither 50% nor 75% fragmentation will achieve this goal.
About the Species
The four ecologically important species that your study focuses on include:
1. Spiny firegrass (SFG): a fictional Eurasian invasive annual grass. It is dangerous because as an annual that dries out in the summer, it increases the risk of dry-season wildfire in habitats that it invades. Elk do not eat SFG unless they are starving. SFG prefers disturbed sites such as roadsides and clearings, and does not do well in the shady environment of a closed forest. It flourishes in direct sunlight. Its effects on human communities include harm to pets and livestock – where it invades, it gets lodged in their noses and mouths, causing serious injury. Its spread also increases the risk of wildfire to homes and businesses.
2. Bluebunch wheatflower (BBWF): a fictional native perennial plant that is a habitat generalist, but is most competitive in moist forest interiors and least competitive in direct sunlight. In all habitats except direct sunlight, it is able to outcompete SFG and prevent the weed’s spread. As the preferred food of elk, it is particularly efficient at outcompeting the annual grass when wolf populations are large enough to moderate herbivore populations.
3. Elk: Elk eat BBWF, but do not find SFG palatable. Their preferred habitat is edges between the forest and clearings. At high numbers, elk eat BBWF, which otherwise suppresses the spread of SFG. When their population is high, elk pose the safety and economic threat of collisions with vehicles, which cause expensive and sometimes deadly damage.
4. Wolves: eat elk. Preferred habitat is intact forest. Wolves are highly sensitive to human disturbance and habitat fragmentation due to (a) getting hit by vehicles and (b) getting shot at by ranchers. They tend to avoid contact with humans, but occasionally prey upon livestock and pets.
The Importance of Forest Ecosystem Services to Your Findings
Your scientific team noted that several citizens of the town with a 50% fragmented forest reserve expressed concern about an increase in flood danger. They told the team that since 50% of the forest was removed and much of the land paved over for development, flood waters in the stream running through town have risen strikingly higher during major precipitation events.
Land trust officials of the town with a 75% fragmented forest reserve reported similar observations. They said that the stream running through town recently flooded the business district for the first time in history, causing millions of dollars in damage. In fact, the mayor told the team that the development the city had allowed seems to have exceeded a threshold of sustainability: it was not only unsustainable for maintaining their forest’s biodiversity, but also for maintaining the forest’s valuable ecosystem service of acting as a sponge that helps mitigate floods.
Investigate the effects of habitat fragmentation associated with deforestation and urban sprawl on forest food webs and ecosystem processes.
Learn how to use the scientific method to address questions in environmental science and apply scientific findings to recommend management solutions.
Determine the percent of intact forest that must be maintained in order to protect the Pinchot Forest Reserve’s biodiversity and ecosystem services.
First, review course readings relevant to this lab:
• Chapter 1, which describes population and community dynamics, including competition between species, food webs and trophic cascades.
• Chapter 4, which describes environmental impacts of deforestation and urban sprawl, including biodiversity loss, fragmentation and increased runoff and flooding.
• Optional supplemental readings (feel free to use these to help answer the Lab Questions)
o Ecological Society of America’s ecosystem services fact sheet (and more in-depth report), which describes the valuable benefits that ecosystems provide to humanity.
o A brief overview article about the impacts of forest fragmentation on biodiversity
o A more detailed scientific review of effects of forest fragmentation on biodiversity
Computer Model Analysis
Click here to view a simulation of the effects of fragmentation on populations of your four key species. Follow the steps below to achieve your team’s objectives.
1. On the screen, you will see:
• Species addition buttons
• Level of fragmentation selection options
• A Graph showing population numbers
2. To explore species population dynamics, first select the 0% fragmented forest, which reflects the current undisturbed state of Pinchot’s forest. Complete the following steps:
a) Simulation Step 1: Add Spiny firegrass (SFG) to the forest ecosystem. In the graph on the screen, a vertical bar graph appears showing the current population of SFG. Record that number in your Excel data table for SFG alone at 0% fragmentation.
b) Step 2: Add Bluebunch wheatflower (BBWF) to the ecosystem. To the right of SFG, a second bar graph appears with a “BBWF” label beneath it, showing its current population. Record both the population number of BBWF and the new population of SFG (as influenced by the addition of BBWF) in your data table.
c) Step 3: Add elk to the ecosystem. Record the population number of elk and the new population sizes of SFG and BBWG (as influenced by the addition of elk) in your data table.
d) Step 4: Add wolves to the ecosystem. Record the population number of wolves and the new population sizes of SFG, BBWG and elk (as influenced by the addition of wolves) in your data table.
3. Adjust the fragmentation level to 25%, 50% and finally 75% and repeat Steps a-d at each level. At each fragmentation level, use your Excel data table to record species population numbers at each step of species addition.
4. When you have completed the data table, answer the study questions below.
In the lab questions below, report your answers in the format of a scientific report: introduction, methods, results, discussion, conclusions and management recommendations. Click here for a tip sheet about writing scientific reports.
1. What is the question that this study aimed to answer? State the hypothesis that you tested.
2. Briefly describe the methods of data collection and analysis you used to test your hypothesis. What scientific procedure did you follow to answer your question and test your hypothesis?
3. Look at your results table. What were impacts of fragmentation on each species’ population numbers when all four were present? Do you accept or reject your hypothesis? Support your answer with reference to the specific results upon which you are basing your finding.
4. Did you observe any thresholds of fragmentation beyond which a species’ population number rapidly declined (here, an example of a threshold would be if one or more species’ population numbers remained relatively constant at 0% and 25% fragmentation, but then suddenly fell dramatically at 50% or 75% fragmentation)? Did the effects of any such threshold on one species cascade through the community to impact other species? Explain, using specific examples from your data.
5. What were the impacts of competition on each species? How did the addition of BBWF, elk and wolves affect the populations of the other species?
6. Which species appear to benefit from increasing fragmentation? Which species are negatively impacted? Based on your knowledge of environmental science, what could explain these observations? Support your answer with specific results from your data and ideas from your readings.
7. How do your findings relate to relevant theories in environmental science? Specifically:
a. Do your results indicate that any of the species are keystone species? Do they support the theory of bottom-up or top-down control of population dynamics in ecosystems? Explain.
b. How do deforestation and urban sprawl affect the greater food web? Do your results support idea that trophic cascades occur in nature? Explain.
8. According to the scenario, your results and the readings, how might the environmental impacts of deforestation and sprawl affect the human community of Pinchot?
Conclusions and Management Recommendations
9. What do you recommend to Pinchot as a “sustainable” level of fragmentation that conserves the forest’s biodiversity and ecosystem services while still allowing for some development? Following up on your answer to question 8, how might conserving Pinchot’s forest reserve protect the town from economic, health and safety threats posed by fragmentation?
Remember – this is a scientific report, so no matter what your opinion of deforestation is, make sure your results and the readings support your conclusions.