The relative influence of competition and prey defences on the trophic structure of animalivorous bat ensembles |
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Authors: | M Corrie Schoeman David S Jacobs |
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Institution: | (1) School of Biological and Conservation Sciences, University of KwaZulu–Natal, Private Bag X54001, Durban, 4000, South Africa;(2) Department of Zoology, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa |
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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. |
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