Predicting climate change impacts on polar bear litter size

Abstract

Predicting the ecological impacts of climate warming is critical for species conservation. Incorporating future warming into population models, however, is challenging because reproduction and survival cannot be measured for yet unobserved environmental conditions. In this study, we use mechanistic energy budget models and data obtainable under current conditions to predict polar bear litter size under future conditions. In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40–73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55–100% if break-up occurs 2 months earlier. Simultaneously, mean litter size would decrease by 22–67% and 44–100%, respectively. The expected timeline for these declines varies with climate-model-specific sea ice predictions. Similar litter size declines may occur in over one-third of the global polar bear population.

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…The die-off of salt marshes results in changes in the behaviour of key grazers (snails) as they seek shelter from predation by blue crabs (Griffin et al, 2011;Silliman et al, 2005). Finally, increased fragmentation of sea ice habitats results in declines in mating success and searching efficiency of top predators such as polar bears (Molnár et al, 2011) and in changes in phototrophic community structure and relative abundance of dominant marine taxa (Mueller et al, 2006).…”

Barents Sea polar bears (Ursus maritimus): population biology and anthropogenic threats

“…Further, later arrival of sea ice in autumn was correlated with lower body mass of adult females and their cubs at den emergence in the spring, suggesting that recent environmental conditions have negatively affected female condition. Body mass is an indication of energy stores (Molnár et al 2009) that are critical for supporting female polar bears during the denning period, when energy is required for maternal maintenance, gestation and nursing (Watts & Hansen 1987;Derocher et al 1993;Molná r et al 2011). Maternal body mass in spring has been positively correlated with body mass of cubs and with cub survival (Derocher & Stirling 1996.…”

“…However, the loss of habitat is symptomatic of larger ecosystem changes that cumulatively may threaten the persistence of polar bears Molnár et al 2010;Molná r et al 2011). Further, the Hopen situation might reflect the situation at other important denning areas in Svalbard where autumn sea ice is necessary for giving pregnant females access to denning habitat (NPI, unpubl.…”

“…Global warming (Comiso 2002;Core Writing Team et al 2007;Comiso et al 2008) is believed to represent a threat to polar bear populations throughout their range on account of the declining area, connectivity ) and suitability of sea-ice habitats for bears (Stirling & Derocher 1993;Derocher et al 2004;Amstrup et al 2008;Wiig et al 2008;Durner et al 2009; Molná r et al 2011). The decrease in habitat for polar bears and their main prey, ringed seals (Pusa hispida), may lead to a reduction in population sizes and possibly to complete loss of some populations (Amstrup et al 2008;Durner et al 2009;Amstrup et al 2010;Molná r et al 2010).…”

Establishing a definition of polar bear (Ursus maritimus) health: A guide to research and management activities

“…Fragmentation and decreased spatial and temporal availability of their sea ice habitat can have negative impacts on the accessibility of their primary prey, i.e., seals (Derocher, 2010;Durner et al, 2009;Wiig, 2005). For example, decreased hunting opportunities and availability of prey can lead to nutritional stress and reduced body size, and may affect reproductive success and survival (Molnár et al, 2011;Regehr et al, 2007;Rode et al, 2010Rode et al, , 2014. In some species, energetic stress may lead to suppression of the immune system and thereby increased mortality and reduced reproductive rates (e.g., Boonstra et al, 2001;Wayland et al, 2002).…”