The tawny owl, strix aluco, is a bird commonly found around Europe. It has two distinct colors, grey and brown. Based on a number of observation, Karell, by process of elimination, has found that the number of brown owls in comparison to those of grey changes as the climate changes. He observed that when the snow in Finland, where he studied the owls, increased compared to years before, simultaneously the number of brown owls compared to grey ones decreased. Vice versa, when the amount of snow decreased, the amount of brown owls in comparison to grey ones increased. It’s important to understand that this change in color is not like people getting tans in the summer, when the sun’s out, and then becoming pale again in the winter when they are out of sunlight. These owls stay one color throughout their life. This frequent change means that this trait is highly heritable and is, therefore, a good way to observe whether or not the environment has an effect on heritable traits.
Figure 1: According to the chart, the number of grey owls is greater than the number of brown owls.
According to Karell, there was definitely some sort of a connection between climate change and the amount of brown tawny owls. It was evident that brown tawny owls were more sensitive to harsh winters than grey ones were. Karell came up with 3 explanations to this. The first possibility was that the predation of brown owls was more extreme in the snow. Because brown is spotted more in the snow than grey, their enemies found them sooner and more often. However, this theory was knocked because it’s biggest threat, the eagle owl, does not hunt using its eyes. It is similar to playing a game of tag when the tagger is blindfolded. You’re not hiding but they can’t see you and rely on other senses to find you. The second explanation is that the coloration is connected to another trait that effects the survival of the owls such as metabolism or immune system. Third, the coloration requires more energy to stay stabilized and is therefore more vulnerable. There is not enough knowledge to fully understand the second and third explanations; therefore, Karell looked at other information to explain the climate and coloration relationship.
Karell also focused on the fact that not only did the population of the brown owl decrease during harsh winters, but it also increased during lighter winters. This could have been due to microevolution, random changes in genes, or physical changes caused by the environment. The increase in the brown owls was observed in the entire population of Finnish tawny owls. This would be similar to a teacher refusing to believe that they hadn’t assigned homework for the night before even though one had done the assignment she had supposedly assigned. A collection of random coincidences? I think not. Likewise, it would be silly to believe that the entire population of Finnish owls were becoming brown was random. The gene changes were not random. The last theory, in which the owl has the ability to adjust their appearances as a result of the environmental changes, was disproved. Owls are not like chameleons, they stay the same color their whole life. If a change in the amount of brown owls was being observed, it was due to the amount of brown owls being born.
Karell and his team were able to prove that there is microevolution occurring, as seen within the tawny owls, in relation to climate change. Why is this important? This shows that climate changes are affecting natural selection within populations. This is the first piece of evidence that proves that populations are capable of evolving to adjust to climate changes. More information relating to the relationship between evolution and climate changes can be found here.
Works Cited
Karell, P. et al. Climate change drives microevolution in a wild bird. Nat. Commun.2:208 doi: 10.1038/ncomms1213 (2011).
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