Rarefaction Curve Calculator

A rarefaction curve plots estimated species diversity (or richness) against the number of individuals sampled. It shows how diversity accumulates as you sample more individuals, allowing you to assess whether your sampling effort was sufficient to capture the true diversity of a community. The curve typically rises steeply at first and then levels off as sampling approaches completeness.

The diversity order q determines how species abundances are weighted. At q=0, all species count equally regardless of abundance — this gives species richness. At q=1, species are weighted proportionally to their abundance, equivalent to the exponential of Shannon entropy. At q=2, dominant species are emphasised more strongly, equivalent to the inverse of Simpson concentration. Together these Hill numbers provide a comprehensive view of community diversity.

Enter the observed count of individuals for each species as comma-separated numbers. For example, if you observed 15 individuals of species A, 10 of species B, 8 of species C, you would enter: 15, 10, 8. Each number represents one species, and zeros can be omitted. The total of all numbers is your total sample size N.

The rarefaction sample size n is the number of individuals you want to rarefy down to — it must be equal to or less than your total observed individuals. Rarefaction randomly subsamples your community down to n individuals many times (bootstraps) and averages the resulting diversity. This lets you compare diversity across samples with different total abundances on a common footing.

Pielou's evenness (J') measures how evenly individuals are distributed among species, ranging from 0 (completely uneven — one species dominates) to 1 (perfectly even — all species equally abundant). It is calculated as H' / ln(S), where H' is the Shannon index and S is species richness. High evenness means no single species overwhelms the community, indicating a more balanced and often more stable ecosystem.

If the rarefaction curve has levelled off (reached a plateau) by the time you reach your actual sample size, your sampling was likely sufficient to capture most of the diversity present. If the curve is still rising steeply at your observed n, you should collect more samples. The estimated sampling coverage percentage shown in the results also gives a direct indicator — values above 95% suggest good coverage.

Shannon diversity (H') is sensitive to rare species and reflects both richness and evenness; higher values indicate greater diversity. Simpson diversity (1-D) represents the probability that two randomly chosen individuals belong to different species, placing more weight on abundant species. For most ecological comparisons, Shannon index is preferred when rare species matter, while Simpson index is better when dominant species structure is the focus.

Yes — that is one of the primary uses of rarefaction. By standardising all communities to the same number of individuals (the smallest sample size among your communities), you can fairly compare their diversity. Without rarefaction, larger samples will almost always appear more diverse simply because more individuals were collected, making direct comparison misleading.