How can I calculate SD when displaying data as a percentage? Hypothetically, I am trying to make a graph representing the abundance of 4 species in a quadrat. I want to display this as a % of the total number each species represents. Here is an example dataset:
             Rep 1    Rep 2    Rep 3   Total 
Species 1     10        32      21       63
Species 2      2        19      10       31
Species 3     27        28      20       75
Species 4     21         8      19       48
                                         217

Below I have worked out the table with the values displayed as percentages. I have then made a 'mean' percentage, which is made from the rep 1-3 % for each species.
            Rep 1   Rep 1 As %  Rep 2   Rep 2 As %  Rep 3   Rep 3 As %     Mean of all %'s      
Species 1     10      16.67%     32       36.78%      21       30.00%         29.03%
Species 2      2       3.33%     19       21.84%      10       14.29%         14.29%
Species 3     27      45.00%     28       32.18%      20       28.57          34.56%
Species 4     21      35.00%      8        9.20%      19       27.14%         22.12%
Totals:       60     100.00%     87      100.00%      70       100.00%        100.00%

I'd like to display this as a graph to show the average % that this species was viewed in each rep. Therefore I need SD or SE to show how much the % values varied around the mean. If I just calculate SD using the same values as I did for the mean will this work? I'm just not certain as it is a % I'm not sure if it would be changing what the SD is technically showing?
EDIT: Major edit to try and clear it up.
 A: I think I have answered my own question as I was just getting confused. If I am still wrong please let me know...
        Rep 1   Rep 1 As %  Rep 2   Rep 2 As %  Rep 3   Rep 3 As %     Mean of all %'s      
Species 1     10      16.67%     32       36.78%      21       30.00%         29.03%
Species 2      2       3.33%     19       21.84%      10       14.29%         14.29%
Species 3     27      45.00%     28       32.18%      20       28.57          34.56%
Species 4     21      35.00%      8        9.20%      19       27.14%         22.12%
Totals:       60     100.00%     87      100.00%      70       100.00%        100.00%

I have converted into a % for each rep by dividing each value by total number of observations for that rep. If I calculate SD by using the three new values (in the example of Species 1 - 0.1667, 0.3678, and 0.3000) then this SD will still be valid as all the data has been standardised and is still proportionally related.
I think I was getting confused as I was unsure if converting to a % changed what the data represented, but in reality I have just divided all the numbers in the same way to a decimal, keeping them proportional and meaning SD calculations are done the same as always.
