Svalbard Polar Bear Paper Mistakenly Assumes Lack of Genetic Variety Has Destructive Penalties – Watts Up With That?
From Dr. Susan Crockford’s polar bear science
Published on September 8, 2021 |
A new paper released today addresses an animal welfare issue that I have already touched on twice: the theoretical assumption that loss of genetic diversity must harm species survival, although there is little evidence to suggest that it does in real life Case was. For this new study, the authors performed some complicated measurements of genetic diversity loss and inbreeding between and between polar bear populations of the Svalbard region between 1995 and 2016 (see map below) and then modeled what this could do in 100 generations (1210 years) ), with the over-anxious hand-wringing we all expect from such prophecies. As far as I can see, this is all meaningless number crunching with no relation to the real world of polar bears.
To support their claim of harm from loss of genetic diversity, the authors of this paper (Maduna et al. 2021) cite four theoretical papers that assume as fact that loss of genetic diversity is harmful, but not the evidence that substantiate this claim. You never seem to have bothered looking at species that have actually suffered a dramatic loss in genetic diversity. Northern elephant seals, for example, reduced to 20-30 animals more than 100 years ago, have recovered to a population of around 170,000 with extremely little genetic diversity but with no apparent impact on health or survival. Similar genetic bottlenecks and recoveries have been documented in Guadalupe fur seals, foxes from the island of San Nicolas, mouflon sheep, and North Atlantic right whales, which I have discussed in detail here (with references). I discussed the topic again in relation to a similar paper on polar bear genetic diversity in 2016.
What is striking about the lack of this new publication is a quote from the recently published article, which showed that the body condition of Svalbard polar bears had increased significantly between 2004 and 2017 despite a significant decrease in sea ice extent in summer and winter (Lippold et al. 2019 : 988). The paper also did not cite any data collected by the Norwegian Polar Institute showing that adult male body condition on Svalbard has not changed since 1993 or that population numbers have not decreased. Instead, the authors only mention that due to a lack of ice, less pregnant females have reached traditional Denning areas and that bears spent less time feeding on glacier fronts than before (Maduna et al. 2021: 2), as if the only available polar bear data in Regarding the decline in sea ice were negative.
Figure 1 from Maduna et al. 2021
Population bottlenecks during the last glacial maximum when suitable habitat was scarce, and another in the late 1800s / early 1900s due to the willful overhunting of left polar bears with remarkably little genetic diversity but no apparent negative impact on their overall health. Oddly enough, this more recent work by Maduna and colleagues assumes, with no evidence, that a little less genetic diversity could be devastating to Svalbard bears in more than 1,000 years. While the media is expected to tout this as frightening new evidence of what climate change has done (here and here), I’m not impressed.
This is conservation biology the WWF style: the loss of genetic diversity sounds bad to people who don’t know better, but real evidence shows it doesn’t.
References
Lippold, A., Bourgeon, S., Aars, J., Andersen, M., Polder, A., Lyche, JL, Bytingsvik, J., Jenssen, BM, Derocher, AE, Welker, JM and Routti, H. 2019. Temporal trends of persistent organic pollutants in Barents Sea polar bears (Ursus maritimus) in relation to changed eating habits and body condition. Environmental Science and Technology 53 (2): 984-995. https://pubs.acs.org/doi/10.1021/acs.est.8b05416
Maduna, SN, Aars, J., Fløystad, I., Klütsch, CFC, Zeyl Fiskebeck, EML, Wiig, Ø et al. 2021 The reduction in sea ice promotes the genetic differentiation of the Barents Sea polar bears. Proceedings of the Royals Society B 288 (1958): 20211741. https://doi.org/10.1098/rspb.2021.1741 OPEN ACCESS
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