DSC-354 Unit 1: Ecology and Phytogeography Practicals

This experiment involves measuring the hydrogen ion concentration (acidity or alkalinity) of environmental samples using pH indicators or digital meters.

Procedure for Soil pH

• Take 10g of dry soil and mix it with 50ml of distilled water in a beaker.
• Stir well for 30 minutes and allow the suspension to settle.
• Use pH paper or a digital pH meter to record the value.

Significance

pH determines the availability of nutrients to plants. Most crops prefer a neutral to slightly acidic range (pH 6.0 - 7.5).

Plants adapt to extreme water availability conditions through specific structural changes.

Hydrophytes (e.g., Hydrilla, Nymphaea)

• Roots: Poorly developed or absent (anchorage is not a primary need).
• Stems: Spongy with aerenchyma to facilitate buoyancy and gas exchange.
• Leaves: Submerged leaves are often highly dissected; floating leaves have stomata on the upper surface only.

Xerophytes (e.g., Casuarina, Opuntia)

• Roots: Extremely deep and extensive to tap into underground water.
• Stems: Often succulent (fleshy) to store water; may perform photosynthesis (phylloclades).
• Leaves: Reduced to spines or scales; possess sunken stomata and thick cuticles to minimize transpiration.

This method determines the minimum area required to represent the majority of species in a community.

Methodology

1. Lay nested quadrats of increasing sizes (e.g., 10x10cm, 20x20cm, 50x50cm, etc.).
2. Record the cumulative number of species found as the area increases.
3. Plot a graph with Area on the x-axis and Number of Species on the y-axis.
4. The point where the curve levels off (plateaus) indicates the minimal quadrat size.

Frequency indicates the dispersion of a species in an area.

Raunkiaer's Law of Frequency

Raunkiaer classified species into five frequency classes:

• Class A: 1 - 20%
• Class B: 21 - 40%
• Class C: 41 - 60%
• Class D: 61 - 80%
• Class E: 81 - 100%

The Law: In a stable community, the distribution follows the trend: A > B > C >= or <= D < E.

These parameters provide a numerical assessment of species prevalence.

Density

Represents the average number of individuals of a species per unit area.

Abundance

Represents the concentration of a species in those specific spots where it is found.

Sieve analysis is used to determine the percentage distribution of different mineral particle sizes in a soil sample.

Particle Classification

• Sand: 0.05mm - 2.0mm
• Silt: 0.002mm - 0.05mm
• Clay: Less than 0.002mm

Soil with a balanced mix of these three is termed Loam, which is ideal for agriculture due to good drainage and water retention.

Students visit diverse ecological sites (forests, wetlands, or grasslands) to observe natural community interactions.

• Identify dominant species.
• Observe biotic interactions (symbiosis, parasitism).
• Analyze environmental stressors (pollution, human encroachment).

8. Exam Focus: Practical Tips & Viva Prep

Frequently Asked Questions

Q: Why is the Species Area Curve important?
A: It ensures that your sampling size is scientifically valid—neither too small to miss diversity nor too large to waste time.

Q: What is the difference between Density and Abundance?
A: Density counts every quadrat studied, reflecting the average across the whole field. Abundance only counts quadrats where the species was actually present, reflecting its "clumping" behavior.

Common Pitfalls

• Calculation Error: Forgetting to multiply by 100 for frequency.
• Identification: Misidentifying similar-looking grass species during quadrat studies.