A REVISED METHOD FOR ESTIMATING REDUCTION OF NATURAL POPULATIONS EFFECTED BY POISONING

抄録

1. We have reasons to think that the census method using E(Y)=(N-x)p is most highly appreciable in practice for the present, the equation holding on the assumptions that events of capture for marked and unmarked animals are independent of each other and respective probability of the event for both is constant; P of y=(x/P)^β seems to give some underestimate as compared with N, but the index β keeping its meaning as before may still characterize general trap response of a population. Thus a revised method for measuring post-poisoning populations was devised on the basis of principles of the former equation. 2. Field works were executed with Microtus-populations to make practical use of this procedure; the reduction ratio of them was computed as about 0.1 by applying previously known values of P and π for want of the data, the results approximating round numbers of kills which were on biological grounds determined from the consuming frequency of poison baits. The "new object reaction" of the populations was found plainly smaller to the powerful baits than to traps, accordingly, for this species tending to have lesser trappability, enumeration of kills from the consuming frequency of poisons would seem practically of more advantage over estimation by trapping.