Climate and Body Size: Using Woodrats as a Thermometer
Abstract:
One of the fundamental problems in modern ecology is understanding how organisms respond to changes in their environment. This is especially relevant concerning anthropogenic climate change. How will plants and animals adjust to living in a warmer and rapidly changing world? Organisms will respond in one or more of the following ways if conditions become unfavorable: by changing geographic range and location, by adapting or evolving their physiology, or by going extinct. One of the ways animals may adapt is by altering their body size. For this project I investigated how the body size of the genus Neotoma (woodrat) changes with climate.
Methods:
All rasters and shape files were stored in a geodatabase. Data manipulation and maps were done using ArcMap. Most of my images were of the 48-contiguous United States, or of the western US. For this reason, I chose to use the North America Albers Equal Area Conic projection for my map displays. This projection is good for viewing North America with minimal area distortion.
I used the ArcToolbox to convert the ASCII files from PRISM into rasters. I used the raster calculator to normalize all the cell values so that each cell gave temperature in degrees Celsius, and precipitation in millimeters. After plotting my site locations, I used the “Extract Values to Points” tool to extract minimum and maximum temperature, and precipitation from the rasters for all of my modern midden sites. I then exported my appended site attribute tables into Excel, where I plotted body size as a function of temperature and precipitation.
To look at general trends in body size through time, I divided my midden data into the following research ages: Holocene (4,000 – 10,000 yrBP), late Pleistocene (10,000 – 20,000 yrBP), and Modern (<50 yrs old). I did this easily by selecting by attribute. After plotting each sample location by age, I created size categories in the layer properties for each age.