Margalef's Richness Index Calculator

Margalef's Richness Index is a biodiversity metric that measures species richness while accounting for the total number of individuals sampled. It corrects for the fact that larger samples tend to contain more species simply due to sampling effort, giving a more comparable richness score across different sample sizes.

The formula is: D = (S − 1) / log(N), where S is the total number of species and N is the total number of individuals in the sample. The logarithm used is the natural log (base e) in most ecological literature, though some references use log base 10.

Higher values indicate greater species richness relative to the sample size. Values below 2 are generally considered to indicate low biodiversity, values between 2 and 5 indicate moderate richness, and values above 5 suggest high biodiversity. The index is most useful when comparing communities sampled with similar methods.

Margalef's Index is best used when you want a simple, quick measure of species richness that adjusts for sample size. It does not account for the evenness of species distribution (how individuals are distributed among species), so for a fuller picture of biodiversity, pair it with indices like Shannon-Wiener or Simpson's Index.

The index does not factor in species abundance or evenness — two communities with the same S and N but different abundance distributions will yield the same Margalef score. It also assumes that all individuals have an equal chance of being sampled, and the result can vary depending on whether natural log or log base 10 is used.

For a comprehensive biodiversity assessment, consider combining Margalef's Index with the Shannon-Wiener Index (which accounts for evenness), Simpson's Dominance Index, and Menhinick's Index. Together, these provide a more complete picture of community structure and species distribution.

Ecologists and biologists use Margalef's Index to compare biodiversity across different habitats, monitor ecosystem health over time, assess the impact of environmental disturbances, and evaluate conservation efforts. It is widely used in surveys of plant communities, invertebrate populations, fish assemblages, and bird counts.

The subtraction of 1 from S is a mathematical correction that ensures the index equals zero when only one species is present (minimum possible richness). It anchors the scale so that the index increases meaningfully as more species are added relative to the sample size.