Comparing Risk Factors for Population Extinction

✍ Scribed by HIROSHI HAKOYAMA; YOH IWASA; JUNKO NAKANISHI

• Book ID: 102611948
• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 190 KB
• Volume: 204
• Category: Article
• ISSN: 0022-5193
• DOI: 10.1006/jtbi.2000.2018

✦ Synopsis

Extinction risk of natural populations of animals and plants is enhanced by many di!erent processes, including habitat size reduction and toxic chemical exposure. We develop a method to evaluate di!erent risk factors in terms of the decrease in the mean extinction time. We choose a population model with logistic growth, environmental and demographic stochasticities with three parameters (intrinsic growth rate r, carrying capacity K, and environmental noise C

). The reduction in the habitat size decreases carrying capacity K only, whilst toxic chemical exposure decreases survivorship (or fertility) and in e!ect reduces both r and K. We derived a formula for the reduction in habitat size that decrease the mean extinction time by the same magnitude as a given level of toxic chemical exposure. In a large population (large K) or in a slowly growing population (small r), a small decrease in survivorship can cause the extinction risk increase corresponding to a signi"cant reduction in the habitat size. This conclusion depends also on the nonlinearity of dose}e!ect relationship. To illustrate the method, we analyse a freshwater "sh, Japanese crucian carp (Carassius auratus subsp.) in Lake Biwa.