This week’s lab will be a practical assessment on testing evolutionary hypotheses using the skills you have developed over the course of the semester.
The pre-lab quiz is a review of many of the analytical approaches we have used, and includes a nice set of slides put together by your TAs to summarize different kinds of analyses. It is strongly recommended that you complete the pre-lab quiz prior to working on this assessment.
In this class we have emphasized the value of using the computer and an open-source, object-oriented programming language (R) enabling manipulation, analysis and visualization data for the purpose of making evidence-based claims.
You can use your notes, previously developed R scripts, and the internet. Please DO NOT USE EACH OTHER because we are interested in what each individual knows.
To assess your progress, we ask you to analyze data on the survival of Galapagos marine iguanas of different weights during an extreme drought that happened in 1982-1983. The drought was accompanied by a lack of upwelling that drives productivity in the nearshore environment where iguanas live.
The Prompt: Investigate the data, construct evidence, and use the evidence for making one or more claims about whether body size (as measured by iguana weight) is under selection (and if so, what kind of selection). What is the evolutionary effect of the 1982-1983 drought?
Questions to guide your response:
● What is the distribution of iguana weights?
● Are the weight distributions different for those that survived vs. those that died?
● What are the averages and standard deviations of the weights of those that survived vs. those that died?
● Is there a relationship between weight and whether an iguana survived or not?
● Is body size under selection?
● Can you determine whether or not body size will evolve the next generation?
Submit the following:
1) Your evidence-based claim and conclusions. (7 points total for having clearly-written and organized claims and conclusions regarding whether body size is under selection and what the evolutionary impact of the drought is. Must be based on your figures and analyses.)
2) All figures you construct that effectively visualize the data and support your claim (incorporated into the PDF). (5 points total for figure(s) that are relevant to the question and referenced in your claim, and are clear, have useful axis labels, coding, etc., and include a figure legend.)
3) Your R script (copy and paste into the bottom of your response) (3 points for clear and organized code)
The data are here.
Notes about the data: Each row is an independent observation of an iguana. Weight is in grams. For survival, 0 = died, 1 = survived. The dataset has a header row.