Estimating effects of adult male mortality on grizzly bear population growth and persistence using matrix models

We radio monitored a hunted, sexually segregated grizzly bear (Ursus arctos ) population and an unhunted, unsegregated population for demographics and constructed a stage- and age-classified matrix model to test for the effect s of adult male mortality and resulting sexual segregation on population gr owth and persistence. Population parameters in the model were adult female survival, subadult female survival, offspring survival, probability of litt er sizes, and probability of unsuccessful pregnancy. The last three paramet ers were affected by adult male mortality and segregation, the others were not. We compared population growth with and without effects of hunting by h olding adult female and subadult female survival constant and by using hunt ed and unhunted values for offspring survival, litter size, and pregnancy. Population growth (Lambda) showed the greatest elasticity for adult surviva l, subadult survival, offspring survival, litter size, and unsuccessful pre gnancy, in that order. This corresponds with observed anti-infanticide tact ics (sexual segregation) by adult females to maximize their fitness. The hu nted population decreased at a rate of 0.99 whereas the simulated, unhunted population increased at a rate of 1.05. The hunted population was much mor e susceptible to population extinction. Under demographic stochasticity mea n time to extinction was 32 years in the hunted population and 110 years in the unhunted population. Under environmental stochasicity mean time to ext inction was 21 years in the hunted population and 43 years in the unhunted population. We suggest that sexual segregation caused by hunting resident a dult males can result in population decline and can even contribute to rapi d population extinctions when numbers are small. (C) 2001 Elsevier Science Ltd. All rights reserved.