ON THE COMPETITION BETWEEN WHITEFISH SPECIES 337 



the three species primarily as a result of interactive segregation (Brian, 1956) 

 that has found different expressions in the two cases because of differences in 

 the species combinations as well as in the general conditions of the lakes in 

 other respects. Genetical differences within species and selective segregation 

 between species are supposed to play subordinate roles. It is thus suggested 

 that interaction between the three species has forced each species to retire 

 from an unrestricted feeding ecology, typical for whitefish in general, to a 

 more specialized one. 



The remarkable double existance of C. peled as dwarfed plankton eater in 

 Vojmsjon and fast-growing insect-eater in Storavan-Uddjaur where C. 

 lavaretus has taken over its place and the role of plankton-eater, gives reason 

 for stressing the differences in the physical conditions of the lakes in question. 

 Vojmsjon is a narrow and deep lake with a narrow littoral zone. In an 

 oversimplified way it could be called a lake with few whitefish niches. 

 Storavan-Uddjaur, on the other hand, which are wide and shallow lakes 

 with wide littoral zones split into mosaic-shaped complexes with islets, 

 sounds, basins and skerries, could be called lakes with several whitefish- 

 niches, that with this interpretation offer several species of whitefish the 

 possibility of hving side by side, and, moreover, permit one species that in 

 another situation is dwarfed to surpass the other species in individual growth. 



RESTATEMENT OF THE CONCEPT OF COMPETITION 



Following the survey of the factors acting in the competition between the 

 whitefish species, a closer analysis of the competition concept will now be 

 attempted. In the Introduction, competition has been defmed with special 

 regard to the general theme of the Symposium. If a population obtains a 

 bad individual growth, it is certainly adversely affected from the viewpoint 

 of human beings exploiting that population. If for a moment we consider 

 intraspecific competition, the only indication of the success of a particular 

 type is that its offspring attain a supernormal numerical proportion of the 

 population in a sequence of generations. The success in interspecific competi- 

 tion is more complex. Without entering into the question of evolutionary 

 trends, one can state that it is often justifiable to use number as a measure of 

 the success in interspecific competition also. This, however, is not always an 

 adequate method. From Elton's exposition (1946) it is possible to derive the 

 idea that the success in competition may also be judged by the amount of 

 the environmental resources that the species utilizes. This is at least easy to 

 reahze when one regards the problem from the point of view of the situation 

 of the species losing resources. Other things being equal, a change in growth 

 (length or weight) involves a change in the utihzation of the resources. Again, 



