Biodiversity

2026 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Define the terms ecosystem and niche
  2. Explain that biodiversity can be assessed at different levels, including: the number and range of different ecosystems and habitats; the number of species and their relative abundance; the genetic variation within each species
  3. Explain the importance of random sampling in determining the biodiversity of an area
  4. 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
  5. Use Spearman's rank correlation and Pearson's linear correlation to analyse the relationships between two variables, including how biotic and abiotic factors affect the distribution and abundance of species
  6. Use Simpson's index of diversity (D) to calculate the biodiversity of an area, and state the significance of different values of D

Core Definitions

https://cambridgeassistant.com

Ecosystem

An ecosystem is a relatively self-contained unit where living organisms and their non-living environment interact with each other. Think of it as a community of living things (plants, animals, microorganisms) all living together in a particular place, along with all the non-living things around them (water, air, soil, sunlight).

For example, a pond is an ecosystem. It contains living things like fish, frogs, water plants, and algae. It also has non-living things like water, dissolved oxygen, sunlight, and minerals in the mud. All these parts interact - the plants use sunlight to make food, fish eat the plants and smaller animals, and everything depends on the water and oxygen.

Other examples of ecosystems include:

  • Tropical rainforests
  • Sandy deserts
  • Coral reefs

Niche

A niche is the functional role that an organism plays within its ecosystem. This is different from its habitat (where it lives). The niche describes what the organism does - how it gets its food, what it eats, what eats it, how it affects other organisms, and its role in nutrient cycling.

For example:

  • A bee's habitat might be a garden, but its niche includes pollinating flowers while collecting nectar
  • An earthworm's habitat is soil, but its niche includes breaking down dead plant material and aerating the soil

Habitat

A habitat is simply the place where an organism lives. It's the organism's address in nature.

Population, Community, and Related Terms

  • Population: A group of organisms of the same species living in the same area at the same time
  • Community: All the different populations (all the different species) living in the same area at the same time
  • Biotic factors: The living components of an ecosystem (other organisms)
  • Abiotic factors: The non-living components of an ecosystem (temperature, water, oxygen, pH, light)

Sign in to view full notes