What is the primary difference between species richness and species evenness?

Species richness is the total count of different species in a habitat, while species evenness (abundance) describes how close in number each species' population is. A diverse habitat requires both high richness and high evenness.

When comparing two habitats, why might a higher species richness not necessarily mean higher biodiversity?

If one habitat has many species but is heavily dominated by just one (low evenness), it may be less stable than a habitat with fewer species that are more equally distributed. Biodiversity indices like Simpson's $D$ account for this distribution.

How does the Heterozygosity Index ($H$) differ from the Index of Diversity ($D$)?

The Heterozygosity Index measures genetic variation within a single species by looking at allele combinations, whereas the Index of Diversity measures the variety and balance of different species within a whole community.

What is a common error when using a quadrat to measure plant distribution?

Failing to use random sampling is a major error; placing quadrats in 'interesting' or 'easy' spots introduces bias. Researchers should use a grid and random number generator to ensure the sample is representative.

Why is it incorrect to sum all individuals ($n$) and then calculate $\sum n(\sum n - 1)$ for the denominator of the diversity index?

The formula requires calculating $n(n-1)$ for each individual species first, and then summing those products. Summing $n$ first would effectively treat the entire community as a single species, yielding a result of 1.

What mistake is made when using a pitfall trap to measure the biodiversity of a bird population?

Using the wrong sampling tool leads to invalid data; pitfall traps are designed for ground-dwelling invertebrates. Highly mobile or flying organisms like birds require methods like point counts or mist nets.

Define 'Species Richness'.

Species richness is the number of different species present in a particular ecological community, landscape, or region. It does not take into account the relative abundance of those species.

What is the formula for the Heterozygosity Index ($H$)?

$H = \frac{\text{number of heterozygotes}}{\text{number of individuals in the population}}$. It represents the proportion of the population that carries two different alleles at a specific gene locus.

State the formula for the Index of Diversity ($D$).

$D = \frac{N(N - 1)}{\sum n(n - 1)}$, where $N$ is the total number of organisms of all species and $n$ is the number of individuals of each individual species.

Why is 'percentage cover' used in quadrat sampling instead of counting individuals?

Percentage cover is used for species where individuals are difficult to distinguish, such as creeping mosses, grasses, or corals. It provides an estimate of the space occupied by the species rather than a discrete count.

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4. Biodiversity and Natural Resources

Measuring Biodiversity Within a Habitat

Summary

Biodiversity within a habitat is a multi-dimensional measure that accounts for the variety of species, their relative abundance, and the genetic variation within populations. Accurate measurement requires standardized sampling techniques to estimate population sizes and mathematical indices to quantify complexity and stability.

1. Core Concepts of Species Diversity

Species Richness: This is the simplest measure of biodiversity, defined as the total number of different species present in a specific community. While easy to calculate, it is often misleading because it treats a species with one individual the same as a species with thousands.
Species Abundance: This refers to the relative number of individuals within each species. A habitat where all species have similar population sizes is considered to have high 'evenness,' which contributes significantly to overall biodiversity.
Species Diversity: A comprehensive measure that integrates both richness and abundance. High species diversity typically indicates a more stable and resilient ecosystem that can better withstand environmental stressors.

Diagram comparing two habitats with identical species richness but different species abundance/evenness.

2. Quantitative Analysis: Index of Diversity

3. Field Sampling Methodologies

Random Sampling: To avoid observer bias, sampling areas must be selected using random number generators to create coordinates on a grid. This ensures that the data collected is a statistically representative subset of the entire habitat.
Quadrats: These square frames are used primarily for plants or slow-moving animals. Researchers record either the number of individuals or the 'percentage cover' if individual counting is impractical (e.g., for moss or grass).
Specialized Traps: Different organisms require specific tools. Pitfall traps (small containers buried in the ground) capture crawling invertebrates, while kick-sampling is used in aquatic environments to dislodge organisms from stream beds into a net.

4. Measuring Genetic Diversity

5. Key Distinctions in Measurement

6. Exam Strategy & Common Pitfalls