From Dr. Susan Crockford’s Polar Bear Science
Posted on September 8, 2021 |
A new paper published today deals with an animal conservation issue I’ve addressed twice before: the theoretical assumption that loss of genetic diversity must be detrimental to species survival despite there being little evidence that this has been the case in real life. For this new study, the authors carried out some complicated measuring of genetic diversity loss and inbreeding amongst and between Svalbard region polar bear populations between 1995 and 2016 (see map below), and then modelled what this could lead to in 100 generations (1210 years), with the over-anxious hand-wringing we’ve all come to expect from such prophesies. As far as I can see, it’s all meaningless number-crunching without relevance 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 to back up the claim. They apparently never bothered to look at species that have actually suffered dramatic loss of genetic diversity. Northern elephant seals, for example, reduced to 20-30 animals more than 100 years ago, have rebounded to a population of about 170,000 with extremely low genetic diversity but no apparent health or survival repercussions. Similar genetic bottlenecks and recoveries have been documented in Guadalupe fur seals, San Nicolas Island foxes, mouflon sheep, and North Atlantic right whales (among others), which I discussed in detail here (with references). I discussed the issue again in regards to a similar polar bear ‘genetic diversity’ paper in 2016.
Conspicuous by its absence in this new publication is a citation of the recent paper that revealed the body condition of female Svalbard polar bears had increased significantly between 2004 and 2017 despite a pronounced decline in summer and winter sea ice extent (Lippold et al. 2019: 988). Nor did the paper cite data collected by the Norwegian Polar Institute that show the body condition of adult males in Svalbard has not changed since 1993 or that population numbers have not declined. Instead, the authors mention only that reduced numbers of pregnant females have reached traditional denning areas due to lack of ice and that bears have spent less time feeding at glacier fronts than they used to do (Maduna et al. 2021: 2), as if the only polar bear data available in relation to sea ice decline was negative.
Population bottlenecks during the Last Glacial Maximum when suitable habitat was scarce and another in the late 1800s/early 1900s due to wanton overhunting left polar bears with remarkably low genetic diversity but no apparent ill-effects to their overall heath. Oddly, this recent work by Maduna and colleagues assumes without evidence that a bit less genetic diversity could be devastating to Svalbard bears more than 1000 years from now. While the media expectedly promote this as scary new evidence of what climate change has wrought (here and here), I am not impressed.
This is conservation biology done WWF-style: loss of genetic diversity sounds bad to people who don’t know better, but real-world evidence shows it isn’t.
References
Lippold, A., Bourgeon, S., Aars, J., Andersen, M., Polder, A., Lyche, J.L., Bytingsvik, J., Jenssen, B.M., Derocher, A.E., Welker, J.M. and Routti, H. 2019. Temporal trends of persistent organic pollutants in Barents Sea polar bears (Ursus maritimus) in relation to changes in feeding habits and body condition. Environmental Science and Technology 53(2):984-995. https://pubs.acs.org/doi/10.1021/acs.est.8b05416
Maduna, S. N., Aars, J., Fløystad, I., Klütsch, C. F. C., Zeyl Fiskebeck, E. M. L., Wiig, Ø. et al. 2021. Sea ice reduction drives genetic differentiation among Barents Sea polar bears. Proceedings of the Royals Society B 288 (1958): 20211741. https://doi.org/10.1098/rspb.2021.1741 OPEN ACCESS
I shouldn’t need to say it, but, I am not “the opposition”.
I’m a very broad centrist who tries to acquire information, facts and opinions from wherever they may be found.
I’m astounded at those who argue for the reasonableness of loss of diversity whose comments seem to be based pincipally on a ‘dislike’ of those who argue otherwise, rather than addressing the available ‘facts’.
I don’t know Griff or his general views but I can easily determine “what camp he is in” by the largely irrelevant comments made by others. It would be hard to fault his first paragraph in general terms. In specific cases outcomes where diversity has been lost may have seemed to have “gone well enough” but we of course do not know with any certainty what otherwise may have happened, and a single example seldom informs us especially well about the general case.
So. <Shields_up>. OF COURSE loss of genetic diversity is liable to have longer term negative consequences in the general case and in most specific cases. Any increase in genetic diversity occurs over utterly vast periods of time by any sensible measure, and any loss is to be regretted. Such loss may indeed lead to a selection process which results is a more robust dominant subset of the original species in a given set of conditions. But it also necessarily elminates other subsets which might otherwise have been “fitter” in other plausible future selection, and longer term does not guarantee what may have been the fitter subset in the longer term will survive.
In situations where “we” have the ability to prevent loss of diversity at ‘acceptable cost’, not doing so is unlikely to be the optimum choice. What constitutes ‘acceptable’ varies widely with context.
When Griff, or anyone else, says somewhat reasonable (or better) things, I suggest that not slanging them just because of who they are and their overall beliefs is liable to be a good option.
<shields [still] up>
🙂
Russell McMahon
rmcspam+diversity@gmail.com