title: Allee effect in polar bears: a potential consequence of polychlorinated biphenyl contamination.
abstract: Polar bears (Ursus maritimus) from East Greenland and Svalbard exhibited very high concentrations of polychlorinated biphenyls (PCBs) in the 1980s and 1990s. In Svalbard, slow population growth during that period was suspected to be linked to PCB contamination. In this case study, we explored how PCBs could have impacted polar bear population growth and/or male reproductive success in Svalbard during the mid-1990s by reducing the fertility of contaminated males. A dose-response relationship linking the effects of PCBs to male polar bear fertility was extrapolated from studies of the effects of PCBs on sperm quality in rodents. Based on this relationship, an individual-based model of bear interactions during the breeding season predicted fertilization success under alternative assumptions regarding male-male competition for females. Contamination reduced pregnancy rates by decreasing the availability of fertile males, thus triggering a mate-finding Allee effect, particularly when male-male competition for females was limited or when infertile males were able to compete with fertile males for females. Comparisons of our model predictions on age-dependent reproductive success of males with published empirical observations revealed that the low representation of 10-14-year-old males among breeding males documented in Svalbard in mid-1990s could have resulted from PCB contamination. We conclude that contamination-related male infertility may lead to a reduction in population growth via an Allee effect. The magnitude of the effect is largely dependent on the population-specific mating system. In eco-toxicological risk assessments, appropriate consideration should therefore be given to negative effects of contaminants on male fertility and male mating behaviour.
authors.affiliation: Biology Centre of the AS CR, v.v.i., Institute of Hydrobiology, Na Sádkách 7, České Budějovice 370 05, Czech Republic viola.pavlova@hbu.cas.cz.|Arctic Research Centre, Aarhus University, C.F. Møllers Allé 8, Aarhus C 8000, Denmark.|Department of Bioscience, Aarhus University, Frederiksborgvej 399, Roskilde 4000, Denmark.
authors.forename: Viola
authors.identifier: 0000-0002-9319-4611
authors.initials: V
authors.lastname: Pavlova
authors.affiliation: Arctic Research Centre, Aarhus University, C.F. Møllers Allé 8, Aarhus C 8000, Denmark.|Department of Bioscience, Aarhus University, Frederiksborgvej 399, Roskilde 4000, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Nabe-Nielsen
authors.affiliation: Arctic Research Centre, Aarhus University, C.F. Møllers Allé 8, Aarhus C 8000, Denmark.|Department of Bioscience, Aarhus University, Frederiksborgvej 399, Roskilde 4000, Denmark.
authors.forename: Rune
authors.initials: R
authors.lastname: Dietz
authors.affiliation: Arctic Research Centre, Aarhus University, C.F. Møllers Allé 8, Aarhus C 8000, Denmark.|Department of Bioscience, Aarhus University, Frederiksborgvej 399, Roskilde 4000, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Sonne
authors.affiliation: Department of Ecological Modelling, Helmholtz Center for Environmental Research-UFZ, Permoserstraße 15, Leipzig 04318, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Grimm
mesh_terms: D000818:Animals; D004785:Environmental Pollutants / Q000009:adverse effects*; D005260:Female; D005298:Fertility; D006116:Greenland; D008297:Male; D011078:Polychlorinated Biphenyls / Q000009:adverse effects*; D011156:Population Density; D011157:Population Dynamics; D013538:Svalbard; D001503:Ursidae / Q000502:physiology*
chemical_list: D004785:Environmental Pollutants; D011078:Polychlorinated Biphenyls
keywords: Allee effect; male reproduction; polar bears; polychlorinated biphenyls