BIO 377 LAB: Population Projection and Life History Evolution
Vital rates can be used to understand an organism’s population structure, growth, age-or stage-based reproductive value, and responses to changes in vital rates at different ages or stages. These data can be used for both conservation and the study of life history evolution. Note that the data do not have to be very good to get some idea of what is going on:
Great White Sharks: http://homepage.mac.com/mollet/Cc/Cc_list.html (check out the demography link).
Right Whales (neat paper): http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v414/n6863/full/414537a_fs.html
Snow Leopards: http://www.snowleopard.org/islt/pdf_bin/chapron_sl_demography.pdf
Poptools gives us a simple way to access these powerful tools to do our own life history experiments.
GOALS:
(1) Understand how to construct a projection model from life table data
(2) Construct and analyze age-based and stage-based population matrices using Pop Tools.
(3) Understand the concepts of sensitivity and elasticity.
(4) Explore how changing life histories changes the strength of selection and population importance of certain life stages.
Download the excel file “lifetable.xls” from the course info site. This is a life table for the African lion, Panthera leo.
Use poptools to convert this life table to a matrix using the “life table to matrix” function. Choose “pre-breeding census.”
Use poptools to calculate lambda, stable age distribution, and reproductive values and to draw the life-cycle diagram. Make the nodes proportional to reproductive value and the arrows proportional to elasticity.
What is the effect of keeping the number of offspring the same but shifting the reproduction earlier? Plot a graph of lambda versus % reproduction in first time interval, keeping the total number of offspring for a mother that lives through all ages the same (e.g. the sum of mx stays the same), but moving more and more of the offspring earlier.
Exercise II
Download “squirrel.xls” from the lab data site. Make life tables for each of the populations as well as projection matrices. Compare the population growth rates, generation times, reproductive schedules, longevity, and elasticities. State a plausible hypothesis for the difference between the two populations.
You’ll also see an excel file called “Uinta.squirrels.xls” This is the original life table. When you analyze this, do you get any differences from the other life table you used?
Exercise III
If you get bored: Construct your own age-based or stage-based matrices for hypothetical organisms with type I, type II, and type III survivorship curves. Draw the life cycle of each with arrows proportional to sensitivity and elasticity of the transitions, and the size of the stage proportional to the reproductive value at that stage. What conclusions do you draw? Where do you expect selection to act most strongly?