Wednesday, July 20, 2011

What comes now?

Field work is over! Now what? There is something after the field season? Indeed there is, and this part of the research process usually lasts much longer than collecting all our samples. Needless to say, with weather being in the mid-high 90s for the last week and this kind of weather on the horizon, I don’t mind the change of scenery that includes air conditioning! I got a couple requests to talk about this part of the process, what do we do after we have the data and samples from the field season?, so I will do my best to discuss the main part of my work in the lab. To keep things lively and interesting I may also integrate discussions of papers or science news that relate to my research or are otherwise of interest. Also, keep the requests coming for things you would like to see me write about.

I think one of the misconceptions that undergrads have about what its like being an ecologist is that we spend all our time running around in the woods. Unfortunately, that is not the case. When I helped teach an undergrad ecology course, in response to a beginning of the semester survey question on experience with Excel, we had a response along the lines of, he wanted to be an ecologist so learning programs like Excel wasn’t really important. The professor and I thought this was quite funny. When I told this to one of my other grad student friends she said, “If all you did was run around in the woods you would just be a vagabond. You need Excel to go from vagabond to ecologist!” I think that’s a great observation (that you Ms. Mel Toups) because I guess that is a difference between being someone who just likes hiking around outside and someone who is a scientist, and that hiking around in the woods has a larger purpose, involving collecting data, manipulating things in the field, and bringing all that information back into the lab for analysis. So, in my goal to not completely be a vagabond, Excel and other computer related things have become a larger part of my daily life.

The first thing I do when I get a new batch of data is do some exploratory graphing and statistics. This is basically to get an idea of what the data look like, which shows me what the general patterns are and helps me make informed decisions on what the appropriate statistics tests are for this data set.

For example, one of the things I am interested in is what the distribution of ticks on hosts is. In other words, are ticks distributed evenly across all the rodents I caught or are some more parasitized than others? In the 2009 field season, this is what the tick distribution looked like:

The x-axis (horizontal) is the number of ticks per host, the y-axis (vertical) is the number of hosts in each category. This graph shows that there were the most hosts in the zero tick category, most hosts had no ticks, and that few hosts were found with many ticks on them (there was only one host with 33 ticks).

In 2011, this is what the distribution looked like:

There are the same axes on this graph. But you can see that the distribution looks a little different. There appears to be a peak at 1 or 2 ticks, most hosts had 1 or 2 ticks, but there is still a long tail to the distribution, meaning there were still few ticks that had a lot of ticks. Because most classic statistical tests assume your data are “normal” and look like this:

This means that when I do my analysis I have to make sure to tell the program that my data look different, in this case have a “negative binomial” distribution ( We have a great stats consultant on campus that I and others in my lab have talked to before and I will be meeting with her soon to make sure I understand what the appropriate tests are for this data set. I’ll use these statistical tests to see if there are any kinds of hosts (males or females, reproductive or non-reproductive hosts, hosts in certain habitats) that usually have more or less ticks than others. I’ll then extend this to investigating which hosts have tick-borne bacterial infections, but that’s down the road a bit.

So that’s one of the things that I’ve been up to after being back in the lab. I’ll talk about the lab work and tests I’ll be doing in the next post.

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