15
—
1.0607
15
—
1.0607
The Species Richness Calculator computes three measures of species richness: the raw species count (S), Margalef's richness index (DMg), and Menhinick's richness index. While S is the simplest biodiversity measure, it depends heavily on sample size. Margalef's and Menhinick's indices attempt to standardize richness relative to the number of individuals sampled.
Enter the number of species observed and the total number of individuals counted. These indices are widely used in ecological surveys, environmental impact assessments, and conservation monitoring to compare species richness across sites with different sampling efforts.
Three richness measures are calculated:
Species Richness (S) = total number of species observed
Margalef's Index: DMg = (S - 1) / ln(N)
Where N is the total number of individuals. This index corrects for sample size by dividing by the natural log of N.
Menhinick's Index: DMn = S / sqrt(N)
This index divides S by the square root of N. Both indices increase with species richness and decrease with sample size, providing a more comparable measure across samples of different sizes.
Inputs
Results
15 species among 200 individuals gives Margalef's index of 2.64 and Menhinick's of 1.06, indicating moderate richness for a temperate forest.
Inputs
Results
80 species among 5000 individuals gives a Margalef index of 9.27, reflecting the exceptionally high species richness typical of coral reefs.
Raw species count (S) depends heavily on sampling effort. Larger samples almost always contain more species simply because rare species are more likely to be encountered. This makes it impossible to fairly compare richness between sites with different sampling intensities. Standardized indices like Margalef's or rarefaction curves help account for this sampling bias.
Margalef's index partially controls for sample size by dividing (S-1) by the natural logarithm of N. This means that two sites with the same underlying richness but different sample sizes will produce more similar Margalef values than raw S values. However, it still assumes a specific relationship between S and N that may not always hold. Rarefaction is generally a more robust approach.
Rarefaction is a technique that standardizes species richness to a common sample size by randomly subsampling the larger sample down to the size of the smaller sample. It provides an unbiased comparison of richness at equal sampling effort. While Margalef's and Menhinick's indices offer simple corrections, rarefaction is considered more statistically rigorous for comparing richness across samples.
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