Exercice 3 Le tableau suivant reprsente les rsultats de ltude de vgtaux la flore dun milieu forestier Le signe indique la prsence de lespce dans le relev Les espces relevs R1 R2 R3 R4 R5 R6 F IF…
Question
Basic Answer
Step 1: Calculate the frequency (F) for each species.
Count the number of “+” signs for each species across all six relevés (R1 to R6). This count represents the number of times the species was present. Divide this count by the total number of relevés (6) and multiply by 100 to express the frequency as a percentage.
For example:
- Fougère aigle: 2 “+” signs. Frequency = (2/6) * 100% ≈ 33.33%
- Bouleau blanc: 4 “+” signs. Frequency = (4/6) * 100% ≈ 66.67%
Repeat this calculation for all species.
Step 2: Calculate the frequency index (IF) for each species.
The frequency index (IF) is calculated as the number of relevés where the species is present. This is simply the count of “+” signs for each species.
For example:
- Fougère aigle: IF = 2
- Bouleau blanc: IF = 4
Repeat this calculation for all species.
Step 3: Complete the table.
Insert the calculated F (%) and IF values into the table provided.
Step 4: Identify characteristic and accompanying species.
Characteristic species are those with high frequency and frequency index values, indicating they are dominant in the environment. Accompanying species have lower values, indicating they are less prevalent. There is no single threshold to define these categories; it depends on the context and the data. Generally, species with F (%) above 50% and high IF could be considered characteristic.
Step 5: Create a histogram and frequency curve (not shown here).
This step requires graphing the data on millimeter paper. The x-axis would represent the species, and the y-axis would represent the frequency (F %). The histogram would use bars to represent the frequency of each species. The frequency curve would connect the tops of the bars to show the overall distribution. Analyzing the histogram and curve can reveal further insights into the species distribution and community structure.
Final Answer
The final answer requires completing the table with the calculated F (%) and IF values for each species and then interpreting the data to identify characteristic and accompanying species based on the frequency and frequency index. A visual representation (histogram and frequency curve) would further enhance the analysis. Without the completed table, a precise identification of characteristic and accompanying species is not possible.
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