Lab Analysis
Learning Objectives
In this lesson, you will:
- Analyze data from ecological field studies
- Interpret population sampling methods and results
- Evaluate experimental design in ecology research
- Draw conclusions from ecological data sets
Practice Quiz
Analyze these ecology lab scenarios. Click to reveal each answer.
Question 1: A quadrat sampling of a meadow shows 15 dandelions in a 1m x 1m area. If the meadow is 500m x 200m, estimate the total dandelion population.
Answer: Total area = 100,000 m2. Estimated population = 15 x 100,000 = 1,500,000 dandelions.
Explanation: Quadrat sampling assumes uniform distribution. Multiple samples from different locations would give a more accurate estimate.
Question 2: In a mark-recapture study, 50 fish are caught, tagged, and released. Later, 60 fish are caught and 10 have tags. Estimate the population.
Answer: Lincoln-Peterson equation: N = (M x C) / R = (50 x 60) / 10 = 300 fish.
Explanation: M = initially marked, C = total recaptured, R = recaptured with marks. Assumes equal probability of capture and no migration.
Question 3: Why would a researcher use transect sampling instead of random quadrat sampling?
Answer: Transect sampling is better for studying how species distribution changes along an environmental gradient (e.g., from shore to water, or from forest edge to interior).
Explanation: Transects reveal patterns of change across distance, while random quadrats give overall averages.
Question 4: An ecologist finds that dissolved oxygen is 8 mg/L upstream and 2 mg/L downstream of a factory. What can be concluded?
Answer: The factory appears to be causing oxygen depletion, likely through nutrient pollution that leads to algal growth and decomposition (eutrophication).
Explanation: This is correlational evidence. To prove causation, you'd need to test water before and after factory operations, or compare to control streams.
Question 5: A biodiversity study uses the Shannon Diversity Index. Site A has H'=2.3, Site B has H'=1.1. What does this tell you?
Answer: Site A has higher biodiversity. Higher Shannon Index values indicate more species and/or more even distribution of individuals among species.
Explanation: The index considers both species richness and evenness. A site with 10 species but 90% of one species has lower H' than one with more balanced populations.
Question 6: What is a control group in an ecology experiment, and why is it necessary?
Answer: A control group is not subjected to the experimental treatment. It provides a baseline for comparison to determine if changes are due to the treatment or other factors.
Explanation: Example: To test if fertilizer increases plant growth, you need unfertilized plants (control) to compare against fertilized plants (treatment).
Question 7: Data shows invasive species population doubling every year for 5 years, then suddenly leveling off. Explain this pattern.
Answer: Initial exponential growth when resources were abundant, followed by logistic growth as the population approached carrying capacity due to resource limitation.
Explanation: This is typical population dynamics. Even invasives eventually face limiting factors like food, space, or disease.
Question 8: Why might two research teams studying the same ecosystem report different species counts?
Answer: Different sampling methods, different seasons, different locations within the ecosystem, different levels of sampling effort, or different species identification expertise.
Explanation: Ecological sampling always has uncertainty. Standardized protocols and multiple samples help reduce variability.
Question 9: A graph shows primary productivity is highest at mid-latitudes. What factors might explain this pattern?
Answer: Mid-latitudes have good balance of sunlight (not too weak like poles), temperature, and often sufficient water. Tropics may have nutrient-poor soils; poles have low light and cold.
Explanation: Productivity depends on light, temperature, water, and nutrients. The combination of these factors varies with latitude.
Question 10: What sources of error should be reported when presenting population sampling data?
Answer: Sample size, number of replicates, standard deviation/error, assumptions that may not hold (random distribution, no migration, equal catch probability), sampling method limitations.
Explanation: All ecological data has uncertainty. Good science reports this uncertainty rather than presenting estimates as exact values.
Next Steps
- Practice calculating population estimates
- Review graphing and data analysis skills
- Move on to claim-evidence writing when ready