Environmental determinism, and not interspecific competition, drives morphological variability in Australasian warblers (Acanthizidae).

Vicente García-Navas,Les Christidis,Petter Z Marki,Marta Rodríguez-Rey

doi:10.1002/ece3.3925

Abstract

Interspecific competition is thought to play a key role in determining the coexistence of closely related species within adaptive radiations. Competition for ecological resources can lead to different outcomes from character displacement to, ultimately, competitive exclusion. Accordingly, divergent natural selection should disfavor those species that are the most similar to their competitor in resource use, thereby increasing morphological disparity. Here, we examined ecomorphological variability within an Australo‐Papuan bird radiation, the Acanthizidae, which include both allopatric and sympatric complexes. In addition, we investigated whether morphological similarities between species are related to environmental factors at fine scale (foraging niche) and/or large scale (climate). Contrary to that predicted by the competition hypothesis, we did not find a significant correlation between the morphological similarities found between species and their degree of range overlap. Comparative modeling based on both a priori and data‐driven identification of selective regimes suggested that foraging niche is a poor predictor of morphological variability in acanthizids. By contrast, our results indicate that climatic conditions were an important factor in the formation of morphological variation. We found a significant negative correlation between species scores for PC1 (positively associated to tarsus length and tail length) and both temperature and precipitation, whereas PC2 (positively associated to bill length and wing length) correlated positively with precipitation. In addition, we found that species inhabiting the same region are closer to each other in morphospace than to species outside that region regardless of genus to which they belong or its foraging strategy. Our results indicate that the conservative body form of acanthizids is one that can work under a wide variety of environments (an all‐purpose morphology), and the observed interspecific similarity is probably driven by the common response to environment.

Highlights

In order to determine to what extent convergence in the adaptive landscape of functional morphology in acanthizids could have occurred by chance under a nonconvergent process, we compared the fit of the convergent SURFACE model with a simpler initial, single-peak Ornstein-Uhlenbeck model (OU1)
Our results indicate that species belonging to these three main groups overlap along the morphological space defined by the two axes, PC1 and PC2 (Figure S1)
G. albofrontata, endemic of the Chatham Islands and a highly restricted species, represent a distinctive regime that may have undergone divergent evolution recently following colonization by a small founder population from its closest relative G. igata, endemic to New Zealand (Ford, 1985). As this process has occurred relatively recently, we found that the optimum associated to the peak occupied by G. albofrontata fell outside the range of the trait data for PC1 and PC2 (Figure 2c; see Ingram & Kai, 2014)

Summary

Introduction

We integrated climate and species distribution data to characterize species’ abiotic requirements at large scale, and thereby to examine the relationship between environmental (climatic) and morphological traits in a phylogenetic framework (i.e., how phenotypes vary across environments).

Objectives

Results

Conclusion