Biodiversity, sampling & Simpson's Index
How rich and varied is life in a particular place? That is the question of biodiversity, and in this lesson we learn to measure it. We start by pinning down two exact definitions — ecosystem and niche — then meet the three levels at which biodiversity is assessed: the range of ecosystems and habitats, the number of species and their relative abundance, and the genetic variation within each species. Because we cannot count every organism, we learn why sampling must be random, and how to do it fairly with a coordinate grid. Then we work Simpson's Index of Diversity, D = 1 - Σ(n/N)², step by step on the board, and read what a value near 1 or near 0 tells us. Finally we cover the four sampling methods the syllabus names — frame quadrats, line transects and belt transects for organisms that stay put, and mark-release-recapture with the Lincoln index, N = (n1 × n2) / n3, for animals that move.
By the end you should be able to (NSSCAS Biology (AS) 1.2):
- Define ecosystem and niche
- Explain that biodiversity can be assessed at different levels: the number and range of different ecosystems and habitats; the number of species and their relative abundance; the genetic variation within each species
- Explain the importance of random sampling in determining the biodiversity of an area
- Use Simpson's Index of Diversity (D) to calculate the biodiversity of an area, and state the significance of different values of D (formula: D = 1 - (Σ(n/N)^2))
- Describe and use suitable methods to assess the distribution and abundance of organisms in an area, limited to frame quadrats, line transects, belt transects and mark-release-recapture using the Lincoln index
- Investigate the distribution and abundance of species in a local area, using the methods above / suitable methods
Miss Rachel and Mike talk through the whole topic — with the figure and working drawn live.