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

Species richness is the total count of different species in an area, while species evenness describes how close in numbers each species in an environment is. A habitat with high evenness is considered more diverse than one where one species dominates.

When should a researcher choose systematic sampling over random sampling?

Systematic sampling should be used when there is a clear environmental gradient or change in the habitat, such as a transition from a meadow to a forest. It allows researchers to see how species distribution changes at specific intervals along that gradient.

How does a point quadrat differ from a frame quadrat in practice?

A frame quadrat is a square used to estimate percentage cover or density within its boundaries, whereas a point quadrat uses a frame with holes for long pins. Only the organisms touched by the pins are recorded, providing a more objective measure of frequency.

What is a common error when calculating Simpson's Index of Diversity ($D$)?

A frequent mistake is calculating the sum of $(n/N)^2$ but forgetting to subtract that value from 1. The final index $D$ must represent the probability that two individuals randomly selected belong to different species, which requires the '1 minus' step.

Why might the Lincoln Index provide an inaccurate estimate of population size?

Inaccuracies occur if the population is not 'closed' (meaning births, deaths, or migration happened between samples) or if the marking method makes the animals more vulnerable to predators, reducing the number of marked individuals available for recapture.

What error occurs if a researcher only takes two or three samples in a large field?

This results in a non-representative sample due to the 'effect of chance.' Small sample sizes are likely to miss rare species or over-represent a localized cluster of one species, leading to an inaccurate biodiversity assessment.

Define 'Species Richness' in the context of biodiversity.

Species richness is a qualitative measure of the number of different species present in a particular ecosystem, landscape, or region. It does not take into account the abundance of the species or their relative population distributions.

What is a 'Transect' in ecological sampling?

A transect is a line (line transect) or a narrow strip (belt transect) placed across a habitat. It serves as a path along which standardized measurements or samples are taken to study the distribution of organisms across an area.

What is the purpose of a Tullgren Funnel?

A Tullgren funnel is used to extract small invertebrates from soil or leaf litter samples. A light and heat source at the top drives the organisms downward through a mesh into a collection flask containing a preservative.

Why is high species evenness often associated with high ecosystem stability?

High evenness suggests that no single species dominates the resources. This distribution means that if one species is affected by a disease or environmental change, other species can fill its functional role, preventing the entire ecosystem from collapsing.

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4. Biodiversity, Evolution & Disease

Sampling to Determine Biodiversity

Summary

Sampling is a fundamental ecological technique used to estimate the biodiversity of a habitat by analyzing representative subsets. It involves measuring species richness and evenness through various physical collection methods and mathematical indices like Simpson's Index of Diversity and the Lincoln Index for mobile populations.

1. Core Concepts of Biodiversity

Species Richness: This refers to the total number of different species present in a specific habitat. While a high count indicates a diverse ecosystem, richness alone does not account for how individuals are distributed among those species.
Species Evenness: This measures the relative abundance of each species. A habitat where all species have similar population sizes is considered more even, and therefore more diverse, than one dominated by a single species.
Biodiversity Significance: High biodiversity typically indicates a stable, resilient ecosystem capable of withstanding environmental changes, whereas low biodiversity often suggests a stressed or fragile environment.

2. Sampling Strategies

Random Sampling: Sites are selected using a coordinate system and random number generators to eliminate researcher bias. This is most effective in uniform habitats where there is no clear environmental gradient.
Systematic Sampling: Samples are taken at fixed intervals, often along a transect (a line or belt). This method is used to observe how biodiversity changes across an environmental gradient, such as moving from a shore inland.
Sample Size and Representation: To ensure data is representative, a large number of samples must be taken. This minimizes the impact of chance and ensures that rare species are more likely to be recorded.

A diagram showing a sampling grid with randomly placed blue quadrats and an orange dashed transect line representing systematic sampling.

3. Techniques for Different Organisms

4. Quantitative Analysis: Simpson's Index

5. Estimating Animal Populations: Lincoln Index

6. Key Distinctions

7. Exam Strategy & Tips