Evaluation of Two Approaches to Defining Extinction Risk under the U.S. Endangered Species Act

Area of Science:

• Conservation Biology
• Decision Theory
• Ecological Economics

Background:

• Current extinction risk assessments predominantly use the cumulative distribution function (CDF) of extinction time relative to a fixed time horizon.
• This method presents limitations in weighting extinctions occurring before or after the arbitrary time horizon.

Purpose of the Study:

• To develop and propose an alternative definition of extinction risk based on decision theory principles.
• To compare the performance of the proposed expected loss (EL) approach against the traditional CDF method.

Main Methods:

• Formulated extinction risk as the expected loss (EL) to society from species extinction, incorporating time preference and risk aversion.
• Compared the EL approach with the CDF approach using real-world and hypothetical species extinction time distributions.

Main Results:

• The EL approach continuously weights extinction time without an artificial horizon, unlike the CDF method.
• Parameters for the EL approach (time preference, risk aversion) are grounded in natural phenomena, allowing nonarbitrary specification.
• The CDF approach's arbitrary time horizon critically influences results and weights all pre-horizon extinctions equally.

Conclusions:

• The expected loss (EL) approach is recommended as a superior method for defining and assessing extinction risk.
• The EL approach offers a more nuanced and ecologically relevant framework for conservation biology decision-making.