ASSESSING THE RISK OF EXTINCTION FOR THE BROWN BEAR (URSUS-ARCTOS) INTHE CORDILLERA CANTABRICA, SPAIN

The status of the brown bear (Ursus arctos) in Spain has suffered a dr amatic decline during the last centuries, both in area and numbers. Cu rrent relict populations are suspected to be under immediate risk of e xtinction. The aim of our model is to attain an understanding of the m ain processes and mechanisms determining population dynamics in the Co rdillera Cantabrica. We compile the knowledge available about brown be ars in the Cordillera Cantabrica, northern Spain, and perform a popula tion viability analysis (PVA) to diagnose the current state of the pop ulation and to support current management. The specially constructed s imulation model, based on long-term field investigations on the wester n brown bear population in the Cordillera Cantabrica, includes detaile d life history data and information on environmental variations in foo d abundance. The method of individual-based modeling is employed to si mulate the fate of individual bears, Reproduction, family breakup, and mortalities are modeled in annual time steps under the influence of e nvironmental variations in food abundance, mortality rates, and reprod uctive parameters. In parallel, we develop an analytical model that de scribes the mean behavior of the population and that enables us to per form a detailed sensitivity analysis. We determine current population parameters by iterating the model with plausible values and compare si mulation results with the 1982-1995 time pattern of observed number of females with cubs of the year. Our results indicate that the populati on suffered a mean annual decrease of similar to 4-5% during the study period, 1982-1995. This decrease could be explained by a coincidence of high poaching pressure with a series of climatically unfavorable ye ars during the period 1982-1988. Thereafter, population size probably stabilized. We estimate that the population currently consists of 25 o r 26 independent females and a total of 50-60 individuals. However, ou r viability analysis shows that the population does not satisfy the cr iterion of a minimum viable population if mortalities remain at the le vel of the last few years of 1988-1995. The ''salvation'' of at least one independent female every three years is required. The population r etains relatively high reproductive parameters, indicating good nutrit ive conditions of the habitat, but mortality rates are higher than tho se known in other brown bear populations. The most sensitive parameter s, adult and subadult mortality of females, form the principal managem ent target. Our model shows that the series of females with cubs conta ins valuable information on the state of the population. We recommend monitoring of females with cubs as the most important management actio n, both for collecting data and for safeguarding the most sensitive pa rt of the population.