The Relative Influence of Competition and Prey Defenses on the Phenotypic Structure of Insectivorous Bat Ensembles in Southern Africa

Abstract

Deterministic filters such as competition and prey defences should have a strong influence on the community structure of animals such as insectivorous bats that 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 phenotypic structure of insectivorous bat ensembles in southern Africa. We used null models to simulate the random phenotypic patterns expected in the absence of competition or prey defences and analysed the deviations of the observed phenotypic pattern from these expected random patterns. The phenotypic structure at local scales exhibited non-random patterns consistent with both competition and prey defense hypotheses. There was evidence that competition influenced body size distribution across ensembles. Competition also influenced wing and echolocation patterns in ensembles and in functional foraging groups with high species richness or abundance. At the same time, prey defense filters influenced echolocation patterns in two species-poor ensembles. Non-random patterns remained evident even after we removed the influence of body size from wing morphology and echolocation parameters taking phylogeny into account. However, abiotic filters such as geographic distribution ranges of small and large-bodied species, extinction risk, and the physics of flight and sound probably also interacted with biotic filters at local and/or regional scales to influence the community structure of sympatric bats in southern Africa. Future studies should investigate alternative parameters that define bat community structure such as diet and abundance to better determine the influence of competition and prey defences on the structure of insectivorous bat ensembles in southern Africa.

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

“…This ecomorphological paradigm predicts that animalivorous bats with similar morphology should occupy similar habitats, while large morphological differences should restrict some species to particular habitats (Jacobs and Barclay 2009;Saunders and Barclay 1992). We previously investigated the role of two deterministic processes, competition and prey defences, on the phenotypic structure of animalivorous bat ensembles (sensu Fauth et al 1996) in South Africa and found non-random patterns consistent with both the competition and prey defence hypotheses (Schoeman and Jacobs 2008). Here, we focus on the influence of these two processes on another niche axis, namely, diet.…”

“…At the same time, prey defences could also influence the dietary composition of the functional groups. Specifically, peak echolocation frequencies used by clutter-edge bats are usually within the best hearing range of tympanate insects (Schoeman and Jacobs 2008). It can therefore be expected that these syntonic bats should only take non-tympanate prey and inattentive tympanate prey if prey defences are 100% effective (Table 1).…”

“…It can therefore be expected that these syntonic bats should only take non-tympanate prey and inattentive tympanate prey if prey defences are 100% effective (Table 1). Conversely, peak echolocation frequencies used by clutter bats and open-air bats are usually above and below the best hearing range of tympanate insects, respectively Schoeman and Jacobs 2008); hence, it can be expected that these allotonic bats eat both eared and noneared prey. However, if prey defences are effective and clutter or open-air bats compete with clutter-edge bats for trophic resources, then clutter and open-air bats should eat mainly tympanate prey (Table 1).…”

Ecological correlates of small mammal assemblage structure at different spatial scales in the savannah biome of South Africa

“…Further, most studies have focused on the influence of either biotic or abiotic processes. Such processes operate over multiple spatio-temporal scales and may overlap with each other (Lawton 2000, Schoeman andJacobs 2008). To disentangle the processes behind species composition patterns, it is necessary to test multiple theories with the same data set that covers different habitats at varying spatial and temporal scales.…”

High duty cycle echolocation and prey detection by bats

“…However, the role of competition in bat assemblages remains unclear. Some authors suggest that competition might structure bat communities and influence patterns of echolocation (Schoeman and Jacobs, 2008), but several disagree (Arita, 1997;Stevens and Willig, 1999;Jiang et al, 2008;Meyer and Kalko, 2008).…”