If you have postgresql on hand, then it's as easy as :

create table data(
month text,
zone integer,
replicate integer,
speciesa integer,
speciesb integer,
speciesc integer);

copy data from stdin with delimiter ',';

sept,1,1,5,10,15
Sept,1,2,0,5,10
Sept,1,3,5,0,5
Sept,2,1,5,5,5
Sept,2,2,10,15,10
Sept,2,3,0,0,5
\.

select month, zone, replicate, avg(speciesa), stddev(speciesa) from da
+ta group by month,zone, replicate;


 month | zone | replicate |          avg           | stddev 
-------+------+-----------+------------------------+--------
 Sept  |    1 |         2 | 0.00000000000000000000 |       
 Sept  |    2 |         3 | 0.00000000000000000000 |       
 Sept  |    1 |         3 |     5.0000000000000000 |       
 Sept  |    2 |         2 |    10.0000000000000000 |       
 sept  |    1 |         1 |     5.0000000000000000 |       
 Sept  |    2 |         1 |     5.0000000000000000 |       
(6 lignes)
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