The 2009 survey is an outlier--everyone was more likely to express support for evolution than they were in the surrounding years. I'm not sure why the results from this survey should be so different from the others, but I noticed that it focused on science, while the others had a mix of topics. So perhaps people felt more inclined to go along with the scientific consensus after answering a lot of questions on science and technology. Another possibility is that people who didn't have much knowledge of science or faith in science were less likely to agree to participate in a survey on science. In any case, any comparison involving the 2009 results should be taken with a grain of salt.
If you omit the 2009 survey, partisan differences have become a bit wider over the whole period, not because Republicans have become less likely to believe in evolution, but because Democrats and independents have become substantially more likely to believe in it.