Use the calculator to compute (1) the percent of total species observed in a sample using P = (S/T) × 100, and (2) common ecological dominance metrics based on relative abundance (Simpson Dominance D and Berger–Parker d). The calculator can also solve for any missing variable when the others are known.

Dominance Index Calculator

Percent Species Observed: P (S/T)
Simpson Dominance (D)
Berger–Parker (d)

Enter any 2 values to calculate the missing variable

Formulas Used

The calculator includes a simple species coverage percentage and two common dominance indices based on species abundances.

P = (S / T) * 100
D = \frac{\sum n_i(n_i-1)}{N(N-1)}
d = N_{\max} / N

Variables:

  • P is the percent of total species observed in the sample (%)
  • S is the number of species observed in the sample
  • T is the total number of species in the reference population/list
  • D is Simpson’s dominance (a proportion from 0 to 1), using species counts
  • ni is the number of individuals of species i
  • N is the total number of individuals across all species (N = Σni)
  • d is the Berger–Parker dominance (a proportion from 0 to 1)
  • Nmax is the number of individuals in the most abundant species

For P, divide the number of species observed in your sample (S) by the total number of species in the reference population/list (T). Multiply by 100 to express it as a percentage. For dominance based on abundance, use the Simpson or Berger–Parker tabs and enter the count of individuals for each species.

What is a Dominance Index?

In ecology, a dominance index quantifies how strongly one species (or a few species) dominates a community based on relative abundance. When one species makes up a large share of the individuals, dominance is higher; when individuals are more evenly distributed among species, dominance is lower. Common dominance indices include Simpson’s dominance (D) and the Berger–Parker index (d).

How to Calculate Percent Species Observed (P) and Dominance Indices

The following steps outline how to calculate the percent of total species observed (P). For dominance based on abundance, use the Simpson or Berger–Parker tabs and enter per-species individual counts.

  1. Determine the number of species observed in the sample (S).
  2. Determine the total number of species in the reference population/list (T).
  3. Use the formula P% = (S / T) × 100.
  4. Calculate P, or check your result with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Number of species observed in the sample (S) = 15

Total number of species in the reference population/list (T) = 50, so P% = (15 / 50) × 100 = 30%.