Some Ecological Aspects of Polymorphism in the Red Squirrel Sciurus vulgaris L. in Northern Europe

Abstract

Comparisons between samples of squirrels taken from the same districts at intervals of several years have revealed that the populations concerned had preserved their polymorphic balance unchanged, or nearly so, in seven out of ten instances. This was true for the populations within the southern half of Finland as well as for those lying farther north on different sides of a steep transition zone in the middle of the Finnish mainland. From the latter, the samples were taken at intervals of about ten years, from the former, at intervals of three years. Within the remaining three populations out of the ten studied, significant changes occurred in 1946. The morphs affected were not, however, the same in all three populations, ruling out the possibility of any common environmental change as a cause of these shifts. Rather, it seems likely that population movements were the basis for the disturbances. In 1949 the populations had apparently recovered from the disturbances occurring in 1946. This year was a so-called peak year during which mass movements took place. A mass migration as such could not be the sole cause of the shifts in the polymorphic balance, but the cause was presumably differential migration, or differential survival, or both, of the morphs within the emigrating populations. After three years at the latest, the polymorphic balance was invariably restored to the typical condition of the district or zone. From previous experience it is known that most if not all of the migrants perish and thus do not contribute to the gene pool of the populations native to the area into which migration occurred. Pe3IoMe nlpH cpaBHeHHH 3K3eMIIJi0poB 6enoK rioAMaHHIX B TeX wKe CaMbIX paROHax C HHTepBaiJaMH B HeCKOJIBKO nIeT OKa3aJIoCb, XTO 3TH HonyiYJIsgHH COXpaHHJIH ileiiHKOM HRJI HO'TH ileiJHKOM CBOt IIOJIHIMOp4FHbIi 6anaHC B CeMH H3 AeCITH cjiy'IaeB. 3TO OTHOCHTCS K IIOIYJ1ILHqM B IOXHOA '{aCTH CTpaHBI a TaKxCe K IUO1YJIqILlIM o6uTaiOIIIHM ceBepHee nepexoAHOR 3OHbU B JJeHTpajIbH6Or ()HHJDIHAXH. 143 nocnexHero paiROHa 6parnR 6eJIOK C IIHTepBaJIOM B 10 neT, H3 nepBoro C HHTepBaJIOM B 3 roxga. CpegiH 3 HI3 AeCATH HCCciegOBaHHbIX HoHyJiLiZHR 6UIH{ 3aMeTHbI B 1946 rogy 3HatHTejIbHbIe H3MeHeHHI. OKa3anocb BCeK-TaKH, 4TO MOp4ThI C H3MeHeHHIMH He 66IJIH Te wce B 3THX HOIYJILIXHAX, a 3TOT 4DaKT BbIKJIO'IaeT BJIHSHHe CpegxbI KaK IIPRH'HHY 3THX H3MeHeHHII. HaM Ka)KeTCSI, ITO HO Bceil BiepOATHOCTH gBHxeHHe flOnyJISIIRHZ ABnReTCS HpIPIHOR 3THX H3MeHeHH}I. HonynsnuuI 1949 roxa no-BHAHMoMy oInpaBHJIHCL nocne nopaKeHHA 1946 r. B 3TOM roxAy HpOH30JIO MaCCOBOe ABHeKeHle 6enoK. Ho MaccoBoe ABH)KeHHe He Mornjo 6bITb ex]RHOA IpHHHOA H3MeHeHHir noaHMop4)HiecKoro 6anIaHca, nIO Bcelk BepOATHOCTH, 3TOA IIPHI}HHOA ABJnReTCS AH;b4bepeH9HajihHoe nepe,BHsweHHe HjH )Ke Ai4xepeHLsHajibHoe BbI4KHBaHHe MOp4b cpe;RH MHrpIpyIioLxHx nonynHALXH4, a MO)KeT 6bITb, YTO 3TH o6a 4raKTopa BMeCTe. 3a riOC3Iie)HHX Tp}i roAa Mop4)oj1orH'eCKH14 6aniaHc 6bIIn 6e3 H4CKJIIO4eHHfA CHOBa BOCCTaHOBJIeH AO npeXHerO THiH'IecKoro COCTOHHAS B paAIOHe HJIH B 3oHe. 3To COOTBeTCTByeT HaiLIeMy paHHemy OIIbITY, ITO 6o0bRHHCTBO MHrpyioiLzx, a MO)KeT 6bITb gaxce Bce rH6HyT H TaKHM o6pa3oM He MOFYT cnoco6CTBoBaTb HOTOKY reHOB cpeAH noHyJIsAHH B HOBOM pailOHe. ,Janee B CTaTbH4 o6cywcKaeTCs HOJuI4MOp4H'IeCKasI npHcrioco6JI~eMOCTb 6enK. Manuscript accepted December 1968.