3.0573
6.2146
19
0.04
25
3.0573
6.2146
19
0.04
25
Margalef's Richness Index Calculator computes a standardized measure of species richness that accounts for the number of individuals sampled. Since raw species counts increase with sample size, Margalef's index provides a more comparable measure by dividing the number of species (minus one) by the natural logarithm of the total number of individuals.
Enter the number of species observed and the total number of individuals. The index increases with species richness and provides a useful metric for comparing sites surveyed with different levels of effort. It is one of the simplest and most widely used richness indices in ecological monitoring.
Margalef's richness index is calculated as:
DMg = (S - 1) / ln(N)
Where S is the total number of species observed and N is the total number of individuals counted. The natural logarithm (ln) is used because the species-area (and species-individuals) relationship is approximately logarithmic.
Subtracting 1 from S ensures that a sample with only one species gives DMg = 0 regardless of sample size. Higher values indicate greater species richness relative to sample size. Values typically range from 0 to about 10 for most ecological communities.
Inputs
Results
20 bird species among 500 individuals yields DMg = 3.06, a moderate richness value typical of temperate deciduous forests.
Inputs
Results
150 insect species from 2000 individuals gives DMg = 19.60, reflecting the extraordinary species richness of tropical insect communities.
There are no universal thresholds, but as a general guide: values below 2 indicate low species richness, 2-5 indicates moderate richness, and values above 5 indicate high richness. However, interpretation depends on the taxonomic group and ecosystem being studied. Insect communities routinely have higher values than vertebrate communities simply because insects are more speciose.
No. Margalef's index is purely a richness measure and does not consider how evenly individuals are distributed among species. A community with 20 species where one species has 90% of individuals has the same Margalef index as one where all 20 species are equally common. For a complete picture of diversity, combine Margalef's index with an evenness measure like Pielou's J.
Margalef's index provides a single summary number and is easy to calculate, making it useful for quick comparisons and routine monitoring. However, rarefaction provides a more rigorous comparison by standardizing to equal sample sizes and showing the species accumulation curve. For publications and detailed analyses, rarefaction or other sample-size-standardized methods are preferred.
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