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Evolution versus Climate Change?

Is it possible that (an example in my "Modeling and Climate Change" talk of) pine beetle damage in the Colorado Rocky Mountains is due to evolution of the beetle rather than global warming?

Environmental changes can be caused by lots of different things. It is known that an extreme cold snap during winter will reduce beetle populations. Therefore, it seems reasonable to think that the booming beetle population is due to relatively mild winters over the last 25 years. Linking the mild winters to global warming is just an educated guess. The mild Colorado winters could easily be related to some more local effect, they could be a statistical anomaly, or the beetle population could be related to other factors. That is why global warming studies need to be global and long term (25 years is short in climate terms).

That said, it seems unlikely that the beetles have evolved to be much more destructive over the last 25 or even 100 years. There are two lines of reasoning that support this. First, there are pine beetles fossils millions of years old in the Florissant fossil beds. They appear identical to the living species. This suggests that they haven't needed to evolve much to survive. Second, evolutionary biologists consider 50,000-100,000 years to be very rapid evolution. On the other hand, trees are apparently killed by a blue fungus carried by one species of beetle. Since fungi can reproduce sexually (which speeds evolution), it seems plausible that the blue fungus might have evolved relatively recently to be more destructive. This is probably still a stretch though.