Estimating the Rate of Species Introductions From the Discovery Record

The discovery record of introduced species reflects a combination of the introduction process and the discovery process. For this reason, the discovery record does not provide a direct proxy for the record of introductions. We describe a general method for estimating the rate of introductions from the discovery record. The method is based on a statistical model of the discovery record that includes both the introduction and discovery processes. The method is illustrated using the discovery record of introduced species in the San Francisco estuary (California, USA). The estimated mean rate of introductions increases from 0.3 introductions in 1850 to 2.3 introductions in 1995.