The relative influence of competition and prey defences on the trophic structure of animalivorous bat ensembles

Abstract

Deterministic filters such as competition and prey defences should have a strong influence on the community structure of animals like animalivorous bats which have life histories characterized by low fecundity, low predation risk, long life expectancy and stable populations. We investigated the relative influence of these two deterministic filters on the trophic structure of animalivorous bat assemblages in South Africa. We used null models to test if patterns of dietary overlap were significantly different from patterns expected by chance and multivariate analyses to test the correlations between diet and phenotype (body size, wing morphology and echolocation). We found little evidence that competition structured the trophic niche of coexisting bats. Contrary to predictions from competition, dietary overlap between bats of ensembles and functional groups (open-air, clutter-edge, and clutter foragers) were significantly higher than expected by chance. Instead, we found support for the predictions of the allotonic frequency hypothesis: there were significant relationships between peak echolocation frequency and the proportion of moths in the diets of bats at local and regional scales, and peak echolocation frequency was the best predictor of diet even after we controlled for the influence of body size and phylogeny. These results suggest that echolocation frequency and prey hearing exert more influence on the trophic structure of sympatric animalivorous bats than competition. Nonetheless, differential habitat use and sensory bias may also be major determinants of trophic structure because these are also correlated with frequencies of bat calls.

Stacking the odds: light pollution may shift the balance in an ancient predator–prey arms race

“…Although light pollution may benefit syntonic species, allotonic bat species may face increased resource competition because of their reliance on eared moths as a primary food resource (Schoeman & Jacobs , ). Further, avoidance of lit environments has been found in several allotonic bat species (Rydell ; Stone, Jones & Harris , ; Lewanzik & Voigt ).…”

“…Moth ears are most sensitive to echolocation calls of common, sympatric bat species (typically 20–50 kHz), allowing them to detect these predators and avoid predation through evasive flight manoeuvres, aposematic signals or echolocation‐jamming calls (Conner & Corcoran ). Syntonic bats produce echolocation calls that are readily detectable by moths and therefore tend to consume very few moths as part of their diet (Schoeman & Jacobs , ). Allotonic bats have evolved echolocation frequencies that fall outside peak sensitivity of moth hearing range, or are of such low amplitude that moths are unable to detect pursuing bats with enough time to successfully evade capture (Goerlitz et al .…”

“…). Allotonic bats are able to circumvent eared‐moth defences and often consume moths as their main prey (Schoeman & Jacobs , ).…”

The influence of feeding on the evolution of sensory signals: a comparative test of an evolutionary trade‐off between masticatory and sensory functions of skulls in southern African Horseshoe bats (Rhinolophidae)

“…We extracted dietary information for the ten species of rhinolophids included in this study from the literature (Whitaker & Black, ; Findley & Black, ; Aldridge & Rautenbach, ; Bogdanowicz et al ., ; Schoeman & Jacobs, , ; Jacobs et al ., ) and regressed the arcsin of the proportion of beetles in their diets against the logarithms of their bite force. Beetles were used because they have a particularly hard exoskeleton.…”

The simple ears of noctuoid moths are tuned to the calls of their sympatric bat community

“…The allotonic frequency hypothesis suggests that some bat species have evolved echolocation calls composed of peak frequencies outside the best hearing ranges of sympatric eared moths and, as a result, consume proportionately more eared moths than do bats calling at frequencies to which moths are most sensitive (Fullard, 1998). Several studies have confirmed a relationship between higher echolocation call frequency and increasing number of moths in the diets of different bat species (Pavey and Burwell, 1998;Schoeman and Jacobs, 2003;Schoeman and Jacobs, 2011;Pavey et al, 2006). In our study, a more detailed measure of the adaptation of moth species to their predator community proves informative.…”