FUN THINGS TO DO WITH BEANS:  Variation, Natural Selection, and Adaptation

 To REVIEW the structure of the simulation:

 The simulation involves populations of two organisms interacting as predator and prey. In each population there was heritable variation in traits which influence success at avoiding capture (prey) or at getting food (predators).  We used variation in these demographic parameters to (survival of prey, feeding success of predators) to drive simulated reproductive success (fitness).  Changes in the frequency of these traits over generations, then, amount to evolution due to natural selection.

 The prey population – the beans – manifested six phenotypes which were simply inherited; in effect, we assumed the reproduction was clonal so that offspring beans were always of the same phenotype as the parent.  We began with a population of 600 beans (100 of each type) spread over a habitat of grassy lawn. 

 The predator population – expressed heritable variation in feeding apparatus (mouthparts);  assumptions about reproduction and inheritance are the same as for beans.

 (NOTE that there could have been significant variation among individuals in other traits as well – e.g., behavioral strategies of predators, or size of beans of same color/pattern.  These variations may have influenced survival and reproductive success, but the simulation does not make assumptions about their heritability, and we did not track differences in success.  You may wish to speculate on some of these phenotypic differences.)

 The rules were simple.  After prey population was established for each generation, predators could pick up prey items with their mouthparts and place it in their stomach; scraping or shoveling directly into the stomach without lifting it from the ground was not allowed -- food has to be picked up with the mouthparts (you are not sea cucumbers).  Once prey entered another predator’s stomach it is no longer available to other predators.  Each generation lasted two minutes.

 At the end of each generation, each predator reproduced according to individual hunting success, with the most successful predators producing more offspring, the least successful producing none.  Prey phenotype  reproduction was proportional to each phenotype’s survival (‘births’ apportioned among surviving individuals so as to bring prey population back to ‘carrying capacity’ each generation). As some of you noted the spatial distribution of the prey population varied somewhat from generation to generation (presumably habitat changed a bit…); this may well have affected the relative success of predator hunting strategies.

 THE RESULTS OF THIS YEAR’S SIMULATION  are in this spreadsheet.

 HERE IS YOUR ASSIGNMENT

     1.  Make some graphs to illustrate the dynamics of predator and prey populations over generational time (i.e., scale on the horizontal axis should represent generations); design these to show important comparisons and differences as clearly as possible.  Follow the usual rules about graphs (e.g., make sure you label axes, make a legend as necessary, etc.).  Explain what you see as the main patterns shown in each graph.  You can do the graphing digitally using whatever software you prefer, or print some graphpaper from a site like www.printfreegraphpaper.com

    2. Interpret the patterns:  Which prey type(s) seem to be best and which least adapted to the environment? Propose a hypothesis  as to how prey characteristics (phenotypic traits) might have caused differences in fitness or 'adaptedness'.  Which predator seems best and which least adapted to feeding on this type of prey?  Offer a hypothesis as to why (put it in terms of FITNESS differences).

     3. You may have noticed other patterns that aren't reflected in the raw data on population numbers (e.g., differences in predator behaviors or diffeences related to the way prey were distributed within their habitat....).  If so, do you have hypotheses for how they might have affected results?  

      4. How did total number of prey killed change over generations?  What do you think this pattern indicates?  (You may want to make a graph of the changes in the total number of prey killed vs. time).

      5. How would you expect the results to change if the exercise were done on gravel?  On a tile floor?

HAND IN WORK BY MONDAY 20 OCT