Chapter 6 practical 5
Aim:
To quantify and compare the rate of species extinction across different historical time periods (pre-historic, historic, and modern) and to understand the primary drivers behind these losses.
1) Species loss tool
Principle:
The rate of species extinction is not constant. By comparing the background extinction rate (the natural rate of species loss) with extinction rates from more recent periods, we can quantify the impact of human activities on global biodiversity. This is often measured in terms of E/MSY (Extinctions per Million Species-Years), which standardizes the rate to allow for comparison across different time scales and groups of species .
Materials Required:
Calculator
Graph paper and ruler
Pencil and eraser
Colored pencils
Data provided by instructor (sourced from the IUCN Red List and scientific publications)
Procedure:
Step 1: Understand the Key Metric - E/MSY
The formula to calculate the extinction rate is:
Extinction Rate (E/MSY) = (Number of Extinctions / (Number of species * Time period)) * 10⁶
Step 2: Define the Time Periods
We will compare three distinct periods:
Period 1: Pre-1500 (Background Rate). Uses the fossil record to establish a baseline.
Period 2: 1500 – 1900 (Early Modern Period). Period of early globalization, colonization, and habitat modification.
Period 3: 1900 – Present (Anthropocene Period). Period of intense industrialization, human population explosion, and climate change.
Step 3: Data Compilation (Provided by Instructor)
The instructor provides a simplified data table based on open-source data from the IUCN Red List for a well-documented group: mammals.
| Time Period | Duration (Years) | Documented Mammal Extinctions | Estimated Total Mammal Species |
|---|---|---|---|
| Pre-1500 | 11,500 | (Fossil background rate) | ~5,500 |
| 1500–1900 | 400 | 32 | ~5,500 |
| 1900–2023 | 123 | 73 | ~5,500 |
Source: Data synthesized from IUCN Red List (www.iucnredlist.org) and scientific literature (e.g., Ceballos et al., 2015).
or
Variable data can be obtained from
https://www.gbif.org/occurrence/charts?q=mammal&iucn_red_list_category=EX
Select Chordata , Select mammalia , Click on number next to mammlia (35,507,797)
Select IUCN Redlist category, Select Extinct species (14,365)
In Section Year, Select different time period (1900-2025, 1600 to 1900)
This provide species went extinct between different time period
Step 4: Calculate the Extinction Rate (E/MSY) for Each Period
Period 2 (1500-1900):
E/MSY = (32 / (5,500 * 400)) * 1,000,000= (32 / 2,200,000) * 1,000,000≈ 14.5 E/MSYPeriod 3 (1900-2023):
E/MSY = (73 / (5,500 * 123)) * 1,000,000= (73 / 676,500) * 1,000,000≈ 107.9 E/MSYPeriod 1 (Background Rate):
The background rate for mammals is given by scientists as ~1 E/MSY (0.1 - 1.0 E/MSY). We will use 1 E/MSY for a conservative comparison.
Step 5: Visualize the Results
,Bar Graph: On graph paper, create a bar graph.,
X-axis: The three time periods.
Y-axis: Extinction Rate (E/MSY). Use a logarithmic scale on a separate graph to better visualize the massive difference.
Draw a horizontal line across the graph at Y = 1 to represent the background rate.
Pie Chart: For the modern period (1900-present), create a pie chart showing the percentage contribution of different anthropogenic drivers (based on provided data: Habitat Loss, Overexploitation, Climate Change, etc.).
Observations:
Table 1: Calculated Extinction Rates
| Time Period | Duration (Years) | Extinctions | Rate (E/MSY) | Multiplier (Compared to Background) |
|---|---|---|---|---|
| Pre-1500 | 11,500 | - | 1.0 | 1x |
| 1500–1900 | 400 | 32 | 14.5 | ~15x |
| 1900–2023 | 123 | 73 | 107.9 | ~108x |
Graph 1: Bar Graph of Extinction Rates (E/MSY)
(A hand-drawn bar graph would be here)
The bar for 1900-2023 is dramatically higher than the others.
The bar for Pre-1500 is a very low baseline.
Pie Chart: Primary Drivers of Modern Extinctions (1900-Present)
(A hand-drawn pie chart would be here)
Habitat Loss/Degradation: 40%
Overexploitation (hunting, trade): 30%
Climate Change: 10%
Invasive Species: 10%
Pollution: 10%
Calculations:
Multiplier for Modern Period: 107.9 E/MSY / 1.0 E/MSY = 107.9 times the background rate.
Result:
The calculated modern extinction rate (107.9 E/MSY) is approximately 108 times higher than the natural background rate (1.0 E/MSY). This acceleration began in the early modern period (~15x background) and has skyrocketed in the last century. The primary driver of modern extinctions is habitat loss.
Discussion:
The Sixth Mass Extinction: An extinction rate 100x above background is a key indicator of a mass extinction event. This provides quantitative evidence that we are in the sixth mass extinction, the Anthropocene extinction, driven by human activity.
Limitations of the Data:
Documentation Bias: Many extinctions, especially of invertebrates and plants, go unrecorded. The true modern rate is likely even higher.
Estimates: The total number of species is an estimate, but as it is a constant in our formula, it does not affect the ratio between periods, which is the most important result.
Why this Matters: Quantifying this loss is the first step toward mitigating it. It provides a stark, numerical basis for urgent conservation policy and action.
Conclusion:
This practical demonstrates that human activities have increased the rate of species extinction by two orders of magnitude compared to the natural baseline. By manually calculating and comparing E/MSY across time periods, we have quantified the profound impact of the Anthropocene on global biodiversity, highlighting the critical need for immediate and sustained conservation efforts.
Viva Voce Questions:
What does E/MSY stand for?
Extinctions per Million Species-Years. It is a standardized unit to compare extinction rates.
What is the significance of the background extinction rate?
It provides a baseline of the natural rate of species loss against which human-caused extinctions can be measured.
Name two primary causes of the increase in extinction rates since 1900.
Habitat destruction and overexploitation of species.
Why is a logarithmic scale useful for the bar graph?
Because the modern extinction rate is so much larger than the background rate, a logarithmic scale allows us to visualize all the bars clearly on a single graph.
What is the "Anthropocene"?
The proposed current geological epoch, characterized by the dominant influence of human activity on Earth's geology and ecosystems.
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