Another assumption is the use of spherical shaped functional individuals. This approach is relevant for small protozoans but cannot systematically apply to protozoans with environmentally adapted shapes (e. g. pennate or centric diatoms) nor it applies to zooplanktonic metazoans with their wealth of shape and sizes \cite{Ki_rboe_2014,Miller_2009}. From there, if one wants to continue to work on functional species bigger than 200µm, we advocate to take in addition with the size the shape of the functional group.