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.

Figure 1. Principal component analysis of wing (WA and WSP) and echolocation (PF and DUR) parameters of 42 southern African insectivorous bat species.

A. Plot of component scores of species on the first two principal components (PC1 and PC2). B. Plot of component weights for echolocation and wing parameters on the first two principal components. Dotted line shows distance to midpoint (0, 0) of graph.

Figure 2. Hierarchical evaluation of the distribution of body sizes of insectivorous bat species at the scale of the Cape Floristic Kingdom (CFK), the Nama-Karoo, the savanna, and southern Africa (SA) source pools.

The expected normal distribution curve is also shown.

Figure 3. Distributions of body sizes of insectivorous bat species at the ensemble scale.

The expected normal distribution curve is also shown..

Figure 4. Distribution of biomes and political boundaries in southern Africa (biomes after [38]).

Locations of the seven insectivorous bat ensembles are indicated with black markers.