Fig.1: Model scheme

Modelling population level effects of chemical contamination in polar bear populations with special regard to PCBs:

An individual-based approach

Viola Pavlova1, Jacob Nabe-Nielsen1, Rune Dietz1,Volker Grimm2, Jens-Christian Svenning3

1National Environmental Research Institute, Department of Arctic Environment, Aarhus University, Roskilde, Denmark 2 Helmholtz Center for Environmental Research – UFZ,Department of Ecological Modelling, Leipzig, Germany

3 Ecoinformatics & Biodiversity Group, Department of Biological Sciences, Aarhus University, Denmark

In order to reconstruct the patterns of contamination levels (concentrations or body burdens) that have been observed in polar bears (Ursus maritimus) in East Greenland between the years 1994-2008 we have constructed an individual based model that incorporates currently available knowledge on polar bear physiology, ecology and toxicology and uses the data on PCB levels (cb 153 only!) in their main prey, ringed seals (Phoca hispida) from the same area and time period. The results allow us to asses whether our current knowledge of mechanisms involved in contamination exposure, dynamics of the contaminant in the bear body and general knowledge of bear biology is good enough to create a realistic model, or which information needs to be collected or verified in the field and to which parameters is the model most sensitive. This model will be later used to simulate population level effects of contaminants by imposing individual health effects in the modeled polar bears .

Methods Model: non-spatial, individual based model, runs in yearly steps in Net Logo platform. The agents represent individual polar bears with main attributes: age, sex, weight, contamination & reproductive status Input data (F.Riget et al., unpubl.): seal growth & contamination

Results & discussion

Acknowledgements:

We gratefully acknowledge the consent kindly given by Frank Riget and ????? to include the data on ringed seals and polar bears from Eastern Greenland in our research. The research was has been financially supported by the European Union under the 7th Framework Programme (project acronym CREAM, contract number PITN-GA-2009-238148.)

Data on seals

Population dynamics: survival & breeding rates of bears in Southern Beaufort Sea population: (Regehr et al 2010) Organochlorine dynamics in females

and lactational transfer to cubs: from Polishuk (1999)

Bear growth and energy requirement: Wa…. mass [kg] at age a W…. asymptotic length k…. mass growth rate constant A…… fitting constant, equation and par. values from Derocher & Wiig (2002) Energy: f…factor adjusting for field metabolic rate E..yearly energy need [kcal/year] (Kleiber 1961) + adjustments for lactating females

3)( )1( AakeWWa −−−=

Hunting seals: every bear conducts random selection of sex and age of each caught seal until the energy requirement is covered => calculate the total cb 153 increment from feeding

References:

Derocher A, Wiig O (2002) Postnatal growth in body length and mass of polar bears (Ursus maritimus) at Svalbard, J. Zool., Lond. 256, 343±349, Kleiber M (1961) The fire of life: an introduction to animal energetics. John Wiley & Sons, Inc., New York Regehr EV, Hunter CM, Caswell H,Amstrup SC, Stirling I (2010) Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice, Journal of Animal Ecology 79, 117–127 Polishuk S (1999) Organochlorine dynamics in free ranging polar bears and their cubs, PhD thesis, University of Saskatchewan

Model predictions: The absolute value of concentration greatly depends on the value of f, a factor which converts the basal energy requirement into field energy requirement, however its value is unknown for polar bears, comparison with real data on contamination of polar bears would however rather support f = 3 or 4, than 2. a) b) The model predicts sex and age dependent patterns in cb 153 concentration similar to those that can be found in the nature, however the absolute values are strongly dependent on values of parameters used for modelling lactational transfer from mother to offspring.

Fig. 4: prediction of tissue concentration of cb 153 in a) 1994 (bottom left) -2008 (upper right) and b) in 2008 only, f = 3 a) b)

75.070365 WafE ⋅⋅=

MALES

FEMALES MALES

FEMALES

SETUP

Predict offspring survival for this year

Calculate energy requirement of each bear

Satisfy energy demand by hunting seals +

calculate total cb153 consumption

Update cb 153 levels according to lactation

calculate cb levels of offspring

Natural mortality + breeding - create new individuals

OUTPUT: Concentration of cb 153 in polar bears for this year

age = age + 1, year = year +1

WHAT IS CREAM? !Mechanistic Effect Models for Ecological Risk Assessment of Chemicals http://cream-itn.eu/!

Fig. 2: Prediction of mean contamination in consecutive years for different values of f…the field metabolic factor (f = 2 (left) and 4 (right), blue - males, red-all bears, lilac-females, year 0 = 1994, all bears older 2 yrs

Fig.3: Comparison of a) model predictions (f =3) and b) real data on polar bear contamination from East Greenland 1994 - 2008 (data by F.Riget)

age

The model tends to overestimate male and underestimate female contamination showing that the loss of body burdens via lactation is probably a too high in the model. The mechanism and parameters of the lactational transfer in polar bears therefore need to be further explored.