Species Richness

Species richness is the number of different species present in a particular area or habitat. It is the simplest way to measure biodiversity within a habitat.It is found by sampling, because it is rarely possible to count every organism in a habitat. Common methods include:1. Quadrats for plants and slow-moving animals, placed at random positions (for example using random coordinates from a grid) to avoid bias.2. Transects, lines along which samples are taken, when conditions change across a habitat.3. Pitfall traps, sweep nets, pond nets and light traps for animals.Every species found is identified, often using an identification key, and the total number of species is counted. Enough samples must be taken to find most of the species present: a useful test is to keep sampling until extra samples find no new species.Example. Samples in a meadow find buttercup, clover, daisy, dandelion, yarrow, plantain and three grass species. The species richness is 9.Species richness is easy to measure and to understand, but it has an important limitation: it does not take into account the number of individuals of each species. A habitat with 9 species in which one grass makes up 95% of the plants has the same species richness as a habitat with 9 species in roughly equal numbers, even though the second is clearly more diverse. Rare species may also be missed in sampling. For these reasons, biologists often use an index of diversity, which includes both the number of species and the number of individuals of each.