Acta Zoologica Cracoviensia, 12() 1967
The Magnitude of Islands and the Size of Bats (Chiroptera)
Abstract:
The study covers the suborder Megachiroptera, with its sole family Pteropidae, and the suborder Microchiroptera, for which representatives of 9 families have been chosen. In the Megachiroptera a decrease in the size of insular forms was found in 15 cases, an increase in 6 cases, whereas in 16 cases there were either no changes in size or they were too complicated for analysis. In the Microchiroptera the insular forms showed a decrease in size in 59 cases and an increase in 26. The cases of the third category (see Megachiroptera) have not been included in the study. The result for both suborders together is 32 increases against 74 decreases, which indicates that the tendency towards reduction in measurements prevails evidently over the opposite tendency. The main cause of the diminution of measurements in the insular Chiroptera is probably the promotion of quantitatively strong populations by selection, which, on the other hand, on account of the limitation of space and, in consequence, among other things, of food supply, is possible by reduction in body size. Inbreeding (less harmful than was supposed before and of rare occurrence owing to the strong dispersal of bats), reduced selection, genetic drift, pleiotropism and gene linkage (these act ambivalently), and Bergmann’s rule (which rather holds good for the temperate zone, where however there are not many islands; besides, it only partly relates to the bats living there because of their slight homeothermy) seem to be of minor importance.
