BIOS 3010: ECOLOGY

Dr Stephen Malcolm

Laboratory 5: Competition

 

 

(1)  Intraspecific Competition:

 

Questions using Populus software:

 

 

by Don Alstad, Dept. Ecology, Evolution and Behavior, University of Minnesota. http://www.cbs.umn.edu/software/populus.html/

 

Java versions of Populus are installed on the laptop computers in the ecology lab.  The following questions can be answered using this software from the desktop icon (P).

 

 

A) POPULATION GROWTH

         1) Density-Independent Growth

 

Using the Continuous model and the gridding function answer the following questions:

i) At N0 = 10 and r = 0.1 what is the population size after 10 generations?                                                                                                

ii) At N0 = 10 and r = 0.5 what is the population size after 10 generations?                                                                                                

iii) At N0 = 10 and r = 1.0 what is the population size after 10 generations?                                                                                                

 

         2) Logistic Population Growth

Using the Continuous model, the gridding function and shifting among graphs answer the following questions at N0 = 5, K = 500, r = 0.2:

i) At what ÒtÓ does the population reach K?                                                 

 

ii) At what population size is dN/dt highest?                                               

 

iii) What is the value of lnK?                                                                           

 

iv) Using the discrete model is there any difference in the model outcome (apart from the discrete time intervals)?                                 

                                                                                                                            

 

 

 

(2) MULTI-SPECIES INTERACTIONS

         1) Lotka-Volterra Interspecific Competition.

 

Using the Lotka-Volterra Competition model set to run to a steady state and the gridding function answer the following questions:

 

At      N1 = 20      r1 = 0.5      K1 = 500    a = 0.5

          N2 = 20      r2 = 0.5      K2 = 500    b = 0.5

i)                               What is the competitive outcome?                                                    

                                                                                                                            

ii) At what population sizes do the N1 and N2 populations end up at when they reach steady state?                        N1 =______N2 =______

iii) Is there a negative impact on the two populations?                              

iv) Is K1 larger or smaller than K2a (give numbers)?                                  

                                                                                                                            

v) Is K2 larger or smaller than K1b (give numbers)?                                   

                                                                                                                            

 

 

At      N1 = 20      r1 = 0.7      K1 = 700    a = 0.7

          N2 = 20      r2 = 0.5      K2 = 500    b = 0.5

i) At what population sizes do the N1 and N2 populations end up at when they reach steady state?                        N1 =______N2 =______

ii) Is K2 > or < than K1b (give numbers)?                                                      

                                                                                                                            

iii) Is K1 > or < than K2a (give numbers)?                                                     

                                                                                                                            

iv) What are the criteria for coexistence in terms of K1, K2, a and b?

                                                                                                                            

                                                                                                                            

 

 

Give your own values for N, r, K, a and b to satisfy the criteria in the following questions.

 

i) if K1 > K2a and K1b > K2 which species wins?                                          

 

ii) if K2a > K1 and K2 > K1b which species wins?                                         

 

iii) Does changing N or r have any impact on the outcome

     of either i) or ii)?                                                                                           

                                                                                                                            

 

iv) if K2a > K1 and K1b > K2 which species wins?                                        

                                                                                                                            

 

v) Does changing N or r have any impact on the outcome

     of iv)?