Community level support for the allotonic frequency hypothesis

The allotonic frequency hypothesis proposes that some insectivorous bats increase their access to moths that can hear echolocation calls by using frequencies to which the ears of the moths are less sensitive. The hypothesis predicts that the frequencies of bat echolocation calls are positively correlated with the incidence of moths in the diet of these bats. Studies that have provided evidence in support of the allotonic frequency hypothesis have relied on data collected by a number of researchers, in a number of different ways and at different times. The aim of this study was to test the allotonic frequency hypothesis on a single African bat community so that data for the different species could be collected at more or less the same time and in the same way. This community consisted of three high duty cycle species, Cloeotis percivali, Hipposideros caffer, and Rhinolophus simulator, and two low duty cycle species, Miniopterus schreibersii and Scotophilus borbonicus. As predicted by the hypothesis, echolocation frequency was positively correlated with the proportion of moths in the diet of these bats. Echolocation frequency was also a better predictor of diet than wing morphology suggesting that the selection pressure exerted by moth hearing might have acted directly on call frequency and secondarily on wing morphology, as part of the same adaptive complex. These results suggest that structure of bat communities might be determined by prey defenses rather than by competition.