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Title (Primary) Assessing the risk of extinction for the brown bear (Ursus arctos) in the Cordillera Cantabrica, Spain
Author Wiegand, T.; Naves, J.; Stephan, T.; Fernandez, A.;
Journal Ecological Monographs
Year 1998
Department OESA;
Volume 68
Issue 4
Language englisch;
Keywords brown bear; endangered species; extinction; individual-based stochastic simulation model; population dynamics; Ursus arctos; viability analysis
Abstract

The status of the brown bear (Ursus arctos) in Spain has suffered a dramatic decline during the last centuries, both in area and numbers. Current relict populations are suspected to be under immediate risk of extinction. The aim of our model is to attain an understanding of the main processes and mechanisms determining population dynamics in the Cordillera Cantabrica. We compile the knowledge available about brown bears in the Cordillera Cantabrica, northern Spain, and perform a population viability analysis (PVA) to diagnose the current state of the population and to support current management.

The specially constructed simulation model, based on long-term field investigations on the western brown bear population in the Cordillera Cantabrica, includes detailed life history data and information on environmental variations in food abundance. The method of individual-based modeling is employed to simulate the fate of individual bears. Reproduction, family breakup, and mortalities are modeled in annual time steps under the influence of environmental variations in food abundance, mortality rates, and reproductive parameters. In parallel, we develop an analytical model that describes the mean behavior of the population and that enables us to perform a detailed sensitivity analysis.

We determine current population parameters by iterating the model with plausible values and compare simulation results with the 1982–1995 time pattern of observed number of females with cubs of the year. Our results indicate that the population suffered a mean annual decrease of 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 years during the period 1982–1988. Thereafter, population size probably stabilized. We estimate that the population currently consists of 25 or 26 independent females and a total of 50–60 individuals. However, our viability analysis shows that the population does not satisfy the criterion of a minimum viable population if mortalities remain at the level of the last few years of 1988–1995. The “salvation” of at least one independent female every three years is required.

The population retains relatively high reproductive parameters, indicating good nutritive conditions of the habitat, but mortality rates are higher than those known in other brown bear populations. The most sensitive parameters, adult and subadult mortality of females, form the principal management target. Our model shows that the series of females with cubs contains valuable information on the state of the population. We recommend monitoring of females with cubs as the most important management action, both for collecting data and for safeguarding the most sensitive part of the population.




Read More: http://www.esajournals.org/doi/abs/10.1890/0012-9615%281998%29068%5B0539%3AATROEF%5D2.0.CO%3B2

The status of the brown bear (Ursus arctos) in Spain has suffered a dramatic decline during the last centuries, both in area and numbers. Current relict populations are suspected to be under immediate risk of extinction. The aim of our model is to attain an understanding of the main processes and mechanisms determining population dynamics in the Cordillera Cantabrica. We compile the knowledge available about brown bears in the Cordillera Cantabrica, northern Spain, and perform a population viability analysis (PVA) to diagnose the current state of the population and to support current management.

The specially constructed simulation model, based on long-term field investigations on the western brown bear population in the Cordillera Cantabrica, includes detailed life history data and information on environmental variations in food abundance. The method of individual-based modeling is employed to simulate the fate of individual bears. Reproduction, family breakup, and mortalities are modeled in annual time steps under the influence of environmental variations in food abundance, mortality rates, and reproductive parameters. In parallel, we develop an analytical model that describes the mean behavior of the population and that enables us to perform a detailed sensitivity analysis.

We determine current population parameters by iterating the model with plausible values and compare simulation results with the 1982–1995 time pattern of observed number of females with cubs of the year. Our results indicate that the population suffered a mean annual decrease of 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 years during the period 1982–1988. Thereafter, population size probably stabilized. We estimate that the population currently consists of 25 or 26 independent females and a total of 50–60 individuals. However, our viability analysis shows that the population does not satisfy the criterion of a minimum viable population if mortalities remain at the level of the last few years of 1988–1995. The “salvation” of at least one independent female every three years is required.

The population retains relatively high reproductive parameters, indicating good nutritive conditions of the habitat, but mortality rates are higher than those known in other brown bear populations. The most sensitive parameters, adult and subadult mortality of females, form the principal management target. Our model shows that the series of females with cubs contains valuable information on the state of the population. We recommend monitoring of females with cubs as the most important management action, both for collecting data and for safeguarding the most sensitive part of the population.




Read More: http://www.esajournals.org/doi/abs/10.1890/0012-9615%281998%29068%5B0539%3AATROEF%5D2.0.CO%3B2

The status of the brown bear (Ursus arctos) in Spain has suffered a dramatic decline during the last centuries, both in area and numbers. Current relict populations are suspected to be under immediate risk of extinction. The aim of our model is to attain an understanding of the main processes and mechanisms determining population dynamics in the Cordillera Cantabrica. We compile the knowledge available about brown bears in the Cordillera Cantabrica, northern Spain, and perform a population viability analysis (PVA) to diagnose the current state of the population and to support current management.




Read More: http://www.esajournals.org/doi/abs/10.1890/0012-9615%281998%29068%5B0539%3AATROEF%5D2.0.CO%3B2

The identification of what factors determine the population dynamics of polyvoltine species has been a difficult problem in ecology because population dynamics can contain intra- and interannual variability, and because the time scale at which factors affect the population is often unknown. We created a comprehensive population model to determine how density dependence (linear, nonlinear, and time-delayed) and weather affected the rate of population growth of white-footed mice (Peromyscus leucopus) in an isolated woodlot. We studied this nonoutbreak, polyvoltine species using a 257-mo data set spanning 23 yr, which incorporated both detailed intra-annual and long-term dynamics, and we used this model to forecast future population size. We then evaluated whether 3-yr spans of monthly data or a 22-yr span of annual data were better able to identify the key determinants that drive population dynamics, and we identified which data type created more accurate forecasts. The 257-mo comprehensive model determined that the intra-annual cycle was caused by seasonally varying intrinsic growth rates and density dependence on a 1-2 mo scale and indicated that peak population size in one year did not affect the population in the subsequent year. Interannual variability in peak and trough density was caused by the effect of weather on monthly rate of growth with a 0-2 mo time delay, with the exception of two droughts. These droughts negatively affected the population for 9 mo; the effects were probably mediated through reduced seed crop. This model explained 81% of the variability in density. Because weather determined interannual variability in density, forecasts that did not use known weather data during the forecast period were poor. When weather data were used, forecasts were accurate within 1-3 animals (10%) of observed densities up to 8 mo in the future but were inaccurate beyond 8 mo. We found that shortterm monthly data detected more factors affecting the population and created more accurate forecasts than long-term annual data, because all factors affecting the population (except droughts) occurred on a monthly scale. The annual model did not detect any weather effects except droughts and detected annual density dependence, which represents time-delayed density dependence in polyvoltine species. We argue that this annual relationship is spurious and caused by studying this polyvoltine species on an inappropriate time scale. Our work suggests that the time scale of the analysis may affect the conclusions drawn about which types of factors determine population size and with what time lag. It also suggests that, even when population fluctuations can be explained, accurately predicting future densities may be impossible when fluctuations are driven by weather

ID 9102
Persistent UFZ Identifier https://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=9102
Wiegand, T., Naves, J., Stephan, T., Fernandez, A. (1998):
Assessing the risk of extinction for the brown bear (Ursus arctos) in the Cordillera Cantabrica, Spain
Ecol. Monogr. 68 (4), 539 - 570