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Bios 3010: Ecology Laboratory 4 Page - 1 
 
BIOS 3010: ECOLOGY 
Dr Stephen Malcolm 
Laboratory 4: Competition & Connell’s barnacles 
 
 
(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?    
Bios 3010: Ecology Laboratory 4 Page - 2 
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 “t” 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 α = 0.5 
  N2 = 20 r2 = 0.5 K2 = 500 β = 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?    
Bios 3010: Ecology Laboratory 4 Page - 3 
iv) Is K1 larger or smaller than K2α (give numbers)?    
   
v) Is K2 larger or smaller than K1β (give numbers)?    
  
 
 
At  N1 = 20 r1 = 0.7 K1 = 700 α = 0.7 
  N2 = 20 r2 = 0.5 K2 = 500 β = 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 K1β (give numbers)?    
   
iii) Is K1 > or < than K2α (give numbers)?    
   
iv) What are the criteria for coexistence in terms of K1, K2, α and β? 
   
   
 
Give your own values for N, r, K, α and β to satisfy the criteria in the 
following questions. 
 
i) if K1β > K2 and K1 > K2α which species wins?    
 
ii) if K2α > K1 and K2 > K1β which species wins?    
 
iii) Does changing N or r have any impact on the outcome 
 of either i) or ii)?    
   
 
iv) if K2α > K1 and K1β > K2 which species wins?    
  
 
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v) Does changing N or r have any impact on the outcome 
 of iv)?    
   
 
 
(3) Interspecific competition between barnacles: The Joseph Connell 
example of Balanus balanoides and Chthamalus stellatus described in 
lecture 6. 
 
Work through the “EcoBeaker” student workbook for “Barnacles and tides” 
and while you do this keep in mind that both abiotic conditions and the 
biotic process of intra- and interspecific competition are at work! 
 
More information about EcoBeaker software is available at the SimBiotic 
Software website at: 
http://www.simbio.com/ 
 
EcoBeaker™: Barnacles and Tides 
 
Description: 
“This is a recreation of the classic experiments of Connell on why the 
barnacles Chthamalus and Balanus have distinct distributions in the rocky 
intertidal zone of Scotland. Students first observe the distributions, then try 
to tease apart the causes through a series of removal and transplant 
experiments. In the more advanced section of the lab, students can add a 
predatory snail, creating a new distribution. This is a popular lab, 
especially for asking students to design and carry out experiments. 
 
PRIMARY CONCEPTS: biotic and abiotic factors; species distributions; 
competition; marine ecosystems”