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 individualbased 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.

Exposure to Persistent Organic Pollutants Reduces Testosterone Concentrations and Affects Sperm Viability and Morphology during the Mating Peak Period in a Controlled Experiment on Farmed Arctic Foxes (Vulpes lagopus)

“…Effects on reproductive organs are important to assess when studying POP exposure in wildlife key species as it affects the demographics and population size via the effect on survival and recruitment. − Investigating the relationship between POPs and sex steroids gives an indication of endocrine disruption and adverse reproductive health effects on, for example, semen quality and testicular dysgenesis syndrome (TDS), which includes development of hypospadias, testicular malign neoplasms, and cryptorchidism . To date, it has not been possible to investigate the relationship between POP exposure and semen quality in any Arctic wildlife species, while several human studies show that exposure to POPs affects semen quality and decreases testosterone concentrations. , …”

A Review of Key Features and Their Implementation in Unstructured, Structured, and Agent‐Based Population Models for Ecological Risk Assessment

“…Other sources of density dependence, such as cooperation and facilitation, can induce an inverse density dependence known as the “Allee effect” (Courchamp et al 1999). In these cases, populations under a certain density threshold have a very low, or even negative, population growth rate, which can increase their likelihood of extinction (Courchamp et al 1999; Pavlova et al 2016). Hence, growth rate actually increases with increasing density.…”

Water pollution: one of the main Limnology challenges in the Anthropocene

“…Polychlorinated biphenyls (PCBs), for example, are compounds that have many industrial applications, such as cooling substances for electrical apparatus, and its biomagnification is a great issue for some organisms, such as polar bears, fishes and even humans (Pavlova et al, 2016;Sobek et al, 2006). Polycyclic aromatic hydrocarbons (PAHs) are well-studied compounds, which are presented in the aquatic environment by effluents and atmospheric deposition and may alter the reproduction and development of organisms (Abdel-Shafy & Mansour, 2016).…”