Chao2 Richness Estimator

Estimate total species richness from incidence (presence/absence) data using the Chao2 estimator (Chao 1987).

Usage

chao2(x)

Arguments

x

A site-by-species matrix (presence/absence or abundance). Automatically binarized.

Value

An object of class spacc_estimate.

Details

The Chao2 estimator is the incidence-based analogue of Chao1: $$S_{Chao2} = S_{obs} + \frac{Q_1^2}{2 Q_2}$$ where \(Q_1\) is the number of uniques (species found at exactly 1 site) and \(Q_2\) is the number of duplicates (species found at exactly 2 sites).

References

Chao, A. (1987). Estimating the population size for capture-recapture data with unequal catchability. Biometrics, 43, 783-791.

See also

chao1() for abundance-based estimation

Examples

species <- matrix(rbinom(50 * 30, 1, 0.3), nrow = 50)
chao2(species)