BIOGEOGRAPHICAL BOUNDARIES 223 



from the total standing crop of animals or the total green pigment. 

 Some of the most interesting results in the Recorder Survey have 

 been obtained from a visual inspection of the green color of the 

 silks, using this to provide a crude estimate of the distribution of 

 phytoplankton. Another useful technique for gross estimations is 

 provided by the C^^ method. On the other hand, it may sometimes 

 be necessary to discover the specific identity of each organism. 

 Obviously the choice of detail in this matter lies with the objective 

 of each investigator. But knowledge of the generic and specific 

 name of an organism may sometimes give a false sense of precision 

 in ecological work. This arises from the dependence of studies of 

 population dynamics on the recognition of "unit stocks" within 

 the species population. Mr. B. B. Parrish of Aberdeen has studied 

 this aspect of fisheries biology and (in a private communication) he 

 defines a unit stock as a subgroup of a species which is self-con- 

 tained biologically, with its own population parameters of repro- 

 duction, growth, and mortality, and which can be treated dy- 

 namically as independent of other subgroups of the species. 



It is often necessary, therefore, to break a species down into 

 separate homogeneous population units, and it may be significant 

 that the greatest complexity of subdivision of this kind has arisen 

 in those organisms which have received most attention from biolo- 

 gists; for example, the herring Clupea harengus and the copepod 

 Calanus finmarchicus. The recognition of separate population 

 types is often dependent on a statistical examination of a large 

 number of individuals in a sample; see, for example, Hill (1959) on 

 American shad. It is possible in some areas to assign an individual 

 herring to one or another type by the recognition of differences in 

 the otoliths (see Parrish and Sharman, 1958). Gushing (1955) 

 followed the changing distribution of separate populations of 

 Calanus finmarchicus by detecting differences in size frequency 

 diagrams. But as Parrish has said, the concept of unit stock does 

 not imply any particular taxonomic status. 



Nevertheless, ecologists and morphologists could profitably 

 work together to maintain the utility of nomenclature and to pre- 

 vent an unwise multiplication of new species and genera. There 



