THE PHENOMENON OF PREDATION — ERRINGTON 519 



The population effects of predation by raptorial birds upon mice and 

 upon songbirds may be equated with the numbers of prey killed; so 

 may predation by the mice and the songbirds upon the insects that 

 these may kill ; so may predation (or parasitism) by insect species upon 

 each other, by the hornets, the dragonflies, the powerful biters and 

 stingers of lesser creatures that cannot escape; and yet I should say 

 that the grounds for imputing population control may be flimsy indeed 

 without consideration of possible intercompensatory adjustments. 



CONCLUSIONS 



To sum up concerning predation as a phenomenon, with special 

 reference to its significance in population control : As may easily be 

 judged, I regard the outstanding source of error in appraisals of preda- 

 tor-prey relationships as confusion of the fact of predation with effect 

 of predation. Apart from a number of extreme or dramatic cases of 

 predation depleting prey populations in ways that are self-evident, my 

 inclmations are to look very critically upon figures presented, by 

 themselves, as proof of population effect. They may constitute no 

 proof at all, however imposing they may be when superficially 

 regarded. 



For intercompensation remains one of the big answers of prey 

 species — especially of the less fecund or the only moderately fecund of 

 prey species — to predation losses as well as to many other losses. On 

 the basis of my own experience as a student of predation, the best ad- 

 vice I have to offer anyone interested in exploring the subject on his 

 own responsibility, or to those trying to obtain workable concepts of its 

 mechanisms, is, in short : Watch out for the compensations in attempt- 

 ing to distinguish between what does or does not count. When com- 

 pensations are important in population dynamics, they simply can- 

 not be ignored in calculations as to regulation effects of mortality 

 factors, if the truth is to be reached. 



