Update: Model Selection and Fieldwork in Maine

The summer session is almost at an end, and the past few weeks have been absolutely packed! I have fully incorporated the milkweed data that we took in the field last month into a new set of models. We now have 4.5 years of data tracking thousands of individual milkweed stems from sprouting/germination until reproduction and dieback at the end of the season each year. This is enough data to make robust statistical models for the vital rates of the population (survival, growth, reproduction), which is what I have been working on. The process of deciding which type of model is the best fit and most suitable for our purposes is a challenging one that takes a surprising amount of time and thought. This stage in the modeling process is often referred to as “model selection” (and validation), and is very heavy on the statistics. Various techniques are used to quantify and visualize how and where a model is performing well and where it may be lacking. A huge part of this involves keeping track of which models can actually be compared with one another in any sort of a meaningful way. This was one of the issue I needed to solve in my analysis. Specifically, we are working with a class of models called Generalized Linear Mixed Models (GLMMs), which do not perform the same way in tests designed for standard linear models. In order to get a more accurate way of assessing the quality of our models, I needed to find and implement some new statistical tools that would make these types of models comparable for us. The below plot is an example of what I used to visually assess the new models, and was generated by the DHARMa package in R. If it looks even remotely interesting to you, check out it’s vignette here.DHARMa Residual Plot

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Update from Washington: More of the Same

Since I last posted, not much has really changed in terms of what I am currently working on. There are still many cards to be looked at for their relevancy to my project and I will then need to scan the important ones for analysis. I’ll admit that this can be at times a bit tedious, but I know that doing this is very important, because there is so much information that can be gained from these cards. It is imperative to gain an accurate understanding about what insects were around American chestnuts before blight was introduced in order to understand what impact blight has had on insect populations. As of right now, I have scanned around 3500 cards and will continue to scan more this week. I will hopefully be done with scanning in the next few days and will then discuss with my mentor what will be the next appropriate step. We will see what happens next!

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Last Week at the Smithsonian: Cards and More Cards

This past week at the Natural History Museum has been a very productive and exciting one. After putting the finishing touches on the two databases I have been working on as described in my previous blog post, I have moved onto a new phase in my research. On the floor below where I am working at the Natural History Museum, there are many drawers filled with cards in a similar style to the Hopkins Cards that contain taxonomic information on insects. To my surprise, there were two full drawers of cards that relate to insect associations on American chestnuts that date back before blight. These cards can prove to be very useful, since they can help me gain an idea of what kind of biodiversity was occurring on American chestnuts before blight was introduced. Upon consultation with my adviser at the Smithsonian, it was determined that I should scan all pertinent cards into a PDF and will then enter their information onto another database. I have so far scanned over 1500 cards and have about half of a drawer left to scan. I hope to begin sifting through the scanned cards and gather important information to help further this project. It will be interesting to see what will happen this week based on what information is gathered from these new cards. Whatever course of action I plan to take, I will definitely have my work cut out for me!

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Update From Washington, DC

After a few weeks of getting used to waking up early and learning what it’s like to be a D.C. commuter, I am now well acquainted with my research at the Smithsonian Natural History Museum. I will admit that I initially struggled to get into a groove that allowed me to be productive, while making sure that I was able to get to D.C. on time. My schedule for the reminder of my time in D.C. consists of waking up at 5:40 AM and then catching the 6:40 commuter bus near my house in Prince William County, Virginia which takes me directly to downtown D.C. I usually arrive (traffic permitting) to the Natural History Museum around 8:00 and leave a little after 4:00 PM to catch the 4:30 bus which on most days allows me to arrive home by 6:15, although there have been days that I haven’t gotten home until 7:00. While this was hard for me at first, I now have no problem waking up early and am able to sleep on the bus to  and from D.C. and have learned to go to bed relatively early. I have developed a newfound respect for commuters and anyone else that has to wake up at very early hours of the day.

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