Polar bears’ fasting period increases as sea ice continues to melt

polar bear. Image by Elizabeth Labunski. Retrieved from https://digitalmedia.fws.gov/digital/collection/natdiglib/id/2761/rec/31

Polar bears (Ursus maritimus) have been experiencing the effects of climate change particularly hard.  Polar bears rely on spring feeding in order to build up fat reserves for the summer-fall fasting period, and as seal pups are birthed, it provides ample opportunity for polar bears to do so.  However, as the global temperature continues to increase, the abundance of sea ice declines.  While polar bears are strong swimmers, they rely on sea ice to use as platforms while they hunt seals.  Without the sea ice, their ability to effectively and efficiently hunt is diminished.  This results in polar bears having less fat storage going into the summer-fall fasting period in which food sources become even more scarce as the bears lose access to marine animals.  Polar bears don’t den during this time, so this period is often referred to as “walking hibernation”.  As the sea ice returns in the winter months, polar bears are once again able to access marine animals for food.  

 

Polar bears have shown increasing signs of fasting over the years.  Between 1985 and 2006, the percent of polar bears in a fasting state in April grew over 300% (Cherry et al., 2009).  The spring months are a time in which polar bears should be feasting to increase fat storages for the coming fasting period.  120-day fasts are typical for male and non-pregnant female polar bears during these summer-fall months (Robbins et al., 2012).  However, this period is predicted to increase to 180 days as temperatures continue to rise.  Over a 180-day fasting period, adult males experience a 28% mortality rate, increased from 3% during a 120-day fast.  

 

This increase in fasting time is even more concerning for pregnant females.  Since pregnant female polar bears den on land during the winter, they will have to go up to 8 months without food.  During the summer-fall fasting period, daily mass loss, energy expenses, and loss of lean mass is much higher than in hibernating bears.  By increasing this fasting period due to climate change, polar bears will go into the winter with less mass than usual. Since heavier females are more likely to produce larger cubs, and thus increase the probability of cub survival, pregnant females want to go into winter with as much fat storage as possible.  It is estimated that pregnant females would need more than 34% body fat leading into the summer-fall fasting period in order to successfully reproduce during the winter (Robbins et al., 2012).

polar bear with cub. Image by Scott Schliebe. Retrieved from https://digitalmedia.fws.gov/digital/collection/natdiglib/id/10931/rec/5

 

As temperatures continue to increase and sea ice continues to melt, the future for polar bears is tenuous.  For pregnant females in particular, an abundant spring is of extreme importance for survival of the summer-fall fasting.  As this fasting period increases due to sea ice melting earlier in the season, more and more polar bears won’t make it through to the winter.  Additionally, pregnant females won’t be able to make it through the fasting with enough fat reserves left to successfully reproduce.  Populations will continue to decrease as reproduction rates fall, making it of the utmost importance to ensure enough sea ice for an abundant spring feast. 

 

 

 

References:

Cherry, S.G., Derocher, A.E., Stirling, I. et al. Fasting physiology of polar bears in relation to environmental change and breeding behavior in the Beaufort Sea. Polar Biol 32, 383–391 (2009). https://doi.org/10.1007/s00300-008-0530-0

Labunski, Elizabeth 2008, Polar bear, U.S. Fish and Wildlife Service, accessed Feb 12, 2024, <https://digitalmedia.fws.gov/digital/collection/natdiglib/id/2761/rec/31>

Robbins, C. T., Lopez-Alfaro, C., Rode, K. D., Tøien, Ø., & Nelson, O. L. (2012). Hibernation and seasonal fasting in bears: The energetic costs and consequences for polar bears. Journal of Mammalogy, 93(6), 1493–1503. https://doi.org/10.1644/11-mamm-a-406.1

Schliebe, Scott 2010, Polar bear with cub, U.S. Fish and Wildlife Service, accessed Feb 12, 2024, <https://digitalmedia.fws.gov/digital/collection/natdiglib/id/10931/rec/5>
Wiig Ø, Aars J, Born EW. Effects of Climate Change on Polar Bears. Science Progress. 2008;91(2):151-173. doi:10.3184/003685008X324506

Fragmentation impact on salamander

I attended a conference activity called Ohio Natural History Conference last weekend and all posters and presentations are super interesting. Among these excellent presentations, one presentation about salamander habitat and population dynamics attracted my attention. The speaker, Dr. Mike Benard, is from Case Western Reserve University and one of the researches his team did was to investigate population dynamics of salamanders under the modification of their habitats, such as habitat loss and new habitat construction. The talk was great and it also invoked me of how fragmented habitats, which means separate habitats, impact salamanders’ reproduction.

Salamanders of Spring | Lake Metroparkshttp://www.lakemetroparks.com/along-the-trail/march-2020/salamanders-of-spring

In the presentation, Dr. Benard and his team sampled the population around a wetland where about 75% of the wetland was removed for the construction of a new sewage plant. I expected that the population of salamanders would decrease due to loss of habitat and limited carrying capacity, which means maximum numbers of individuals can be held in one place. However, in contrast, the population of salamanders increased after a slight decrease due to unknown reasons, which represents that the salamanders gave more births within less habitat (Benard 2022).

On the other hand, the abundance of salamanders was estimated in another area that had a history of agriculture and forest fragmentation. These places were altered artificially after agriculture, including less vegetation and less canopy cover existing. Measured the population of local salamanders, the team found out that the abundance here was quite low (Cosentino & Brubaker 2018). The results reflected that vegetation has a negative relationship with the population of salamanders and forest fragmentation could decrease the reproduction of salamanders (Cosentino & Brubaker 2018).

In addition, calculating the risk of local extinction of salamanders, assuming a population isolated from breeding grounds, was used to assess the possible impact of habitat fragmentation in salamanders’ survival. The parameters were calculated using data from the previous 18 years. Their findings revealed a high likelihood of local extinction of the population under habitat fragmentation. It highlighted the grave repercussions of fragmentation (Bar-David et al. 2007). As a result, terrestrial habitats must be protected, and landscape connectivity must be promoted to allow individuals to migrate between breeding locations for potential escape benefits.

In conclusion, the fragmented habitat has various impacts on the population dynamics of salamanders. For example, low vegetation cover would result in low reproduction rates(Cosentino & Brubaker 2018). And isolated populations could show a negative relationship with salamanders’ survivals(Bar-David et al. 2007). The restoration and protection of habitats and connected populations are necessary.

 

 

 

Reference

Bar-David, Shirli, Ori Segev, Nir Peleg, Naomi Hill, Alan R. Templeton, Cheryl B. Schultz, and Leon Blaustein. Long-Distance Movements by Fire Salamanders (Salamandra Infraimmaculata) and Implications for Habitat Fragmentation. Israel Journal of Ecology and Evolution 53.2:143-159 (2007).

Benard, M. Ambystoma salamander population dynamics during 11 years of habitat modification and restoration. Ohio Natural History Conference (2022).

Cosentino, B.J., Brubaker, K.M. Effects of land use legacies and habitat fragmentation on salamander abundance. Landscape Ecology 33, 1573–1584 (2018).

http://www.lakemetroparks.com/along-the-trail/march-2020/salamanders-of-spring