|[Note Guidelines] Photographer's Note|
|One more post on the theme of elephant seal biology before leaving the beach and dunes of Aņo Nuevo. I'll also apologize in advance for a bit of a lecture beyond seals, but this topic is both important and entirely appropriate for a bunch of nature junkies such as inhabit TN.|
Close to the dunes where the two previous elephant seal shots were taken, this beach allows more room for the seals. Visible in the photo are several times more elephant seals than comprised by the entire species in the 1890s. This is because they suffered what is referred to as a population bottleneck.
The next few paragraphs are compiled/edited from Wikipedia (http://en.wikipedia.org/wiki/Population_bottleneck):
A population bottleneck (or genetic bottleneck) is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing. Population bottlenecks increase genetic drift, as the rate of drift is inversely proportional to the population size. They also increase inbreeding due to the reduced pool of possible mates.
European bison faced extinction in the early 20th century. The animals living today are all descended from 12 individuals and they have extremely low genetic variation, which may be beginning to affect the reproductive ability of bulls. The population of American Bison fell due to overhunting, nearly leading to extinction (an estimated population of 750) around the year 1890 and has since begun to recover.
An example familiar to many non-scientists is cheetahs, which are so closely related to each other that skin grafts from one cheetah to another do not provoke immune responses, thus suggesting an extreme population bottleneck in the past. Another bottlenecked species is the Golden Hamster, of which the vast majority are descended from a single litter found in the Syrian desert around 1930.
A classic example of a population bottleneck is that of Northern Elephant Seals, whose population fell to about 30 in the 1890s although it now numbers in the hundreds of thousands.
And finally, there is significant scientific evidence that humans went through the same kind of bottleneck. All living humans' female line ancestry can be traced back to a single female around 140,000 years ago. Via the male line, all humans can trace their ancestry back to a single male 60,000 to 90,000 years ago.
Now back to my own comments.
What does all this mean? The phenomenon of population bottlenecks is both old and current. The effect on a population is difficult to gauge because biology (i.e. life on this planet) is one very big uncontrolled experiment. However, as noted in the first two Wikipedia paragraphs above, there is plenty of reason to think that genetic bottlenecks are generally harmful to a species. At the very least, they cut down on the genetic potential a species has available for adjusting to threats. They may be, but are not necessarily, prelude to extinction.
As the Earth's human population grows, we will continue to increase our pressure on wildlife habitat. We will overfish lakes and oceans, we will deforest large parts of our remaining undeveloped land, and we will affect populations of wild plants and animals by other means not yet anticipated. We certainly will drive some species to extinction and push others through narrow bottlenecks.
Biodiversity has become a new buzzword, but there is more to the concept than first meets the eye. It seems that in the mind of the general public, biodiversity means having a large total number of species. But population bottlenecks teach us that intraspecies diversity is also very important and that in many species it is seriously endangered. Retaining substantial diversity within a species is a worthy goal and may be essential for the health of that species.
Maintenance of wildlife habitat in the form of protected reserves is essential, and may fend off extinctions, but it may not be enough to prevent serious population bottlenecks. Even large swaths of protected habitat may not be sufficient for some species. Large ocean mammals such as the biggest whales are clearly threatened by population bottlenecks due to past overhunting, even if their total numbers suggest they are not in immediate danger of extinction.
For how many species have we already gone too far? How many valuable genes, representing millions of years of evolutionary fine-tuning, have been lost from wild species? Have we already driven off the cliff or are we just now reaching the edge of a slippery slope down? Though the size of the human population shows we ourselves are not in any danger of extinction, what will our chances be many generations from now if we squander the priceless genetic resource represented by all the other species on our planet?
tech notes- significant rotation and cropping, significant shadow/highlight adjustment and contrast boost, two step sharpening, no color manipulation
notes added 5-10-09
1) This post is logging far more views than my comparable posts, but I can't tell for certain why. I suspect it's because of the comment on genetic bottlenecks, but have no way of knowing without feedback. Any comments would be appreciated, from within TN or from outsiders. Is there some outside link to the page that I don't know about?
2) If you have read this comment and it strikes a chord, then also look at my "two monarchs" post, which presents some more geeky science in a way that should be palatable and digestible to non-scientists. Important message there- have a peek.
Thanks for looking and reading.
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