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Expected minimum population size as a measure of threat
Author(s) -
McCarthy Michael A.,
Thompson Colin
Publication year - 2001
Publication title -
animal conservation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.111
H-Index - 85
eISSN - 1469-1795
pISSN - 1367-9430
DOI - 10.1017/s136794300100141x
Subject(s) - population size , population , extinction (optical mineralogy) , small population size , population viability analysis , range (aeronautics) , minimum viable population , statistics , population growth , effective population size , population decline , population model , econometrics , mathematics , demography , biology , endangered species , sociology , paleontology , materials science , genetic diversity , composite material
Risks of population decline are studied extensively in conservation biology, but are difficult to estimate because they change abruptly over a relatively narrow range of parameters. We propose that risks of decline may be usefully summarized by the expected minimum population size. This is the smallest population size that is expected to occur within a particular time period. Analytical solutions for the expected minimum population size are obtained for a stochastic population model of exponential growth. In more complex models that are analyzed by Monte Carlo simulation, the expected minimum population size may be determined by recording the smallest population size obtained in each iteration and taking the average of these values. Whereas risks of decline change abruptly with changes in parameter values, the expected minimum population size changes more gradually. The results demonstrate that the expected minimum population size provides a better indication of the propensity for decline than the risk of extinction (or risk of decline to some other small population size), especially when the risk of extinction is small.