TY - JOUR A1 - Pavlova, Viola A1 - Grimm, Volker A1 - Dietz, Rune A1 - Sonne, Christian A1 - Vorkamp, Katrin A1 - Riget, Frank F. A1 - Letcher, Robert J. A1 - Gustavson, Kim A1 - Desforges, Jean-Pierre A1 - Nabe-Nielsen, Jacob T1 - Modeling Population-Level Consequences of Polychlorinated Biphenyl Exposure in East Greenland Polar Bears JF - Archives of environmental contamination and toxicology N2 - Polychlorinated biphenyls (PCBs) can cause endocrine disruption, cancer, immunosuppression, or reproductive failure in animals. We used an individual-based model to explore whether and how PCB-associated reproductive failure could affect the dynamics of a hypothetical polar bear (Ursus maritimus) population exposed to PCBs to the same degree as the East Greenland subpopulation. Dose-response data from experimental studies on a surrogate species, the mink (Mustela vision), were used in the absence of similar data for polar bears. Two alternative types of reproductive failure in relation to maternal sum-PCB concentrations were considered: increased abortion rate and increased cub mortality. We found that the quantitative impact of PCB-induced reproductive failure on population growth rate depended largely on the actual type of reproductive failure involved. Critical potencies of the dose-response relationship for decreasing the population growth rate were established for both modeled types of reproductive failure. Comparing the model predictions of the age-dependent trend of sum-PCBs concentrations in females with actual field measurements from East Greenland indicated that it was unlikely that PCB exposure caused a high incidence of abortions in the subpopulation. However, on the basis of this analysis, it could not be excluded that PCB exposure contributes to higher cub mortality. Our results highlight the necessity for further research on the possible influence of PCBs on polar bear reproduction regarding their physiological pathway. This includes determining the exact cause of reproductive failure, i.e., in utero exposure versus lactational exposure of offspring; the timing of offspring death; and establishing the most relevant reference metrics for the dose-response relationship. Y1 - 2016 U6 - https://doi.org/10.1007/s00244-015-0203-2 SN - 0090-4341 SN - 1432-0703 VL - 70 SP - 143 EP - 154 PB - Springer CY - New York ER - TY - JOUR A1 - Pavlova, Viola A1 - Nabe-Nielsen, Jacob A1 - Dietz, Rune A1 - Svenning, Jens-Christian A1 - Vorkamp, Katrin A1 - Riget, Frank Farso A1 - Sonne, Christian A1 - Letcher, Robert J. A1 - Grimm, Volker T1 - Field metabolic rate and PCB adipose tissue deposition efficiency in East Greenland polar bears derived from contaminant monitoring data JF - PLoS one N2 - Climate change will increasingly affect the natural habitat and diet of polar bears (Ursus maritimus). Understanding the energetic needs of polar bears is therefore important. We developed a theoretical method for estimating polar bear food consumption based on using the highly recalcitrant polychlorinated biphenyl (PCB) congener, 2,2',4,4',55-hexaCB (CB153) in bear adipose tissue as an indicator of food intake. By comparing the CB153 tissue concentrations in wild polar bears with estimates from a purposely designed individual-based model, we identified the possible combinations of field metabolic rates (FMR) and CB153 deposition efficiencies in East Greenland polar bears. Our simulations indicate that if 30% of the CB153 consumed by polar bear individuals were deposited into their adipose tissue, the corresponding FMR would be only two times the basal metabolic rate. In contrast, if the modelled CB153 deposition efficiency were 10%, adult polar bears would require six times more energy than that needed to cover basal metabolism. This is considerably higher than what has been assumed for polar bears in previous studies though it is similar to FMRs found in other marine mammals. An implication of this result is that even relatively small reductions in future feeding opportunities could impact the survival of East Greenland polar bears. Y1 - 2014 U6 - https://doi.org/10.1371/journal.pone.0104037 SN - 1932-6203 VL - 9 IS - 8 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Sibly, Richard M. A1 - Grimm, Volker A1 - Martin, Benjamin T. A1 - Johnston, Alice S. A. A1 - Kulakowska, Katarzyna A1 - Topping, Christopher J. A1 - Calow, Peter A1 - Nabe-Nielsen, Jacob A1 - Thorbek, Pernille A1 - DeAngelis, Donald L. T1 - Representing the acquisition and use of energy by individuals in agent-based models of animal populations JF - Methods in ecology and evolution : an official journal of the British Ecological Society N2 - Agent-based models (ABMs) are widely used to predict how populations respond to changing environments. As the availability of food varies in space and time, individuals should have their own energy budgets, but there is no consensus as to how these should be modelled. Here, we use knowledge of physiological ecology to identify major issues confronting the modeller and to make recommendations about how energy budgets for use in ABMs should be constructed. Our proposal is that modelled animals forage as necessary to supply their energy needs for maintenance, growth and reproduction. If there is sufficient energy intake, an animal allocates the energy obtained in the order: maintenance, growth, reproduction, energy storage, until its energy stores reach an optimal level. If there is a shortfall, the priorities for maintenance and growth/reproduction remain the same until reserves fall to a critical threshold below which all are allocated to maintenance. Rates of ingestion and allocation depend on body mass and temperature. We make suggestions for how each of these processes should be modelled mathematically. Mortality rates vary with body mass and temperature according to known relationships, and these can be used to obtain estimates of background mortality rate. If parameter values cannot be obtained directly, then values may provisionally be obtained by parameter borrowing, pattern-oriented modelling, artificial evolution or from allometric equations. The development of ABMs incorporating individual energy budgets is essential for realistic modelling of populations affected by food availability. Such ABMs are already being used to guide conservation planning of nature reserves and shell fisheries, to assess environmental impacts of building proposals including wind farms and highways and to assess the effects on nontarget organisms of chemicals for the control of agricultural pests. KW - bioenergetics KW - energy budget KW - individual-based models KW - population dynamics Y1 - 2013 U6 - https://doi.org/10.1111/2041-210x.12002 SN - 2041-210X VL - 4 IS - 2 SP - 151 EP - 161 PB - Wiley-Blackwell CY - Hoboken ER -