algae/notes/physiological_diversity.htm

Physiological diversity as a strategy in fluctuating environments

March 4, 2002

John Rueter

notes for ESR473

 

These tables are meant to follow up on the ideas presented in:

Efficiency in algal regulation: Comparison of several strategies.

These calculations are based on the same model and spreadsheet presented in that paper.

Hypothesis

The hypothesis of this exploration is that a population (of one species) that maintains a range of cellular compositions will do better in fluctuating light than cells that are either fixed to be one compositional ratio or cells that try to adapt. This is hypothesized to work because the some of the cells are better able to handle fluctuations outside of the normal range. For example a cell that is adapted to L=20 will handle L=10 almost twice as well as a cell that is adapted to L=200, and a cell that is adapted to L=100 will have twice the productivity at L= 200 compared to a cell that is adapted to L=10.

Method

From that model, I made a table of the composition and the growth rates for algae adapted to a range of lights. Each one of these fixed compositions is exposed to a range of light and the instantaneous specific growth rate is calculated. These growth rates and light were used to calculate the cumulative growth for fluctuating light series.

  Adapted to:
incident
light 		10 20 35 50 75 100 200 500
10 .035 .026 .021 .018 .017 .015 .014 .014
20   .051 .041 .035 .032 .027 .026 .025
35     .063 .059 .055 .045 .043 .041
50       .070 .071 .061 .058 .056
        .071 .070 .070 .070
          .070 .070 .070
            .070 .070
             

.070

Table 1. Instantaneous growth rate at given incident lights for cells adapted to a range of light. The values below the diagonal are all at the maximum for that column, i.e. for all incident light > 20 the growth rate is 0.51

Results

Two sets of fluctuating light regimes were constructed that had the same light intensity per hour on average. Each had 10 steps and was repeated 10 times during the 100 hour run

Light regime 1: 10-20-35-50-75-100-200-100-75-50

Light regime 2: 10-10-100-100-50-50-75-75-200-35

Populations were constructed that had a fixed proportion of cells adapted to different light levels. The composition of these cells was fixed during the run, they did not adapt.

Proportion of this class of cell
 Light
regime

 

 final
growth
after
100 hrs
10 20 35 50 75 100 200 500
.2 .2 .2 .2 .2      
1
6968
adaption algorithm run to light regime 1
8372
  .33   .33   .34    
1
8786
        .50 .50    
1
11786
        1.0      
1
14442
      .50 .50      
1
14518
                   
adaptation algorithm run to light regime 2
6054
.14 .14 .14 .14 .14 .14 .02  
2
6470
  .33   .33   .34    
2
7380
  .2 .2 .2 .2 .2    
2
8551
    .1 .4 .4 .1    
2
11606
      .5 .5      
2
12420
        1.0      
2
12475

 

This probing of the possibilities shows that the diversity strategy works very well in mixed environments, better than an allocation adapation algorithm. The more the regime jumps around regime 2), the better it does relative to the allocation algoritm.

Next steps

Both of these regimes had the same light intensity (average light per hour =70.3 ??check this??). These strategies need to be tested in more varied environments and at different average light intensities.

The competition outcome should be set up like this table below.

r
e
g
i
m
e

  average light per hour
  20 35 50 75

cyclic
like regime 1

        
jumpy
like regime 2		        
chaotic