The evolutionary relationship among beak shape, mechanical advantage, and feeding ecology in modern birds*

Abstract

Extensive research on avian adaptive radiations has led to a presumption that beak morphology predicts feeding ecology in birds. However, this ecomorphological relationship has only been quantified in a handful of avian lineages, where associations are of variable strength, and never at a broad macroevolutionary scale. Here, we used shape analysis and phylogenetic comparative methods to quantify the relationships among beak shape, mechanical advantage, and two measures of feeding ecology (feeding behavior and semiquantitative dietary preferences) in a broad sample of modern birds, comprising most living orders. We found a complex relationship, with most variables showing a significant relationship with feeding ecology but little explanatory power. For example, diet accounts for less than 12% of beak shape variation. Similar beak shapes are associated with disparate dietary regimes, even when accounting for diet‐feeding behavior relationships and phylogeny. Very few lineages optimize for stronger bite forces, with most birds exhibiting relatively fast, weak bites, even in large predatory taxa. The extreme morphological and behavioral flexibility of the beak in birds suggests that, far from being an exemplary feeding adaptation, avian beak diversification may have been largely contingent on trade‐offs and constraints.

The association between morphological and ecological characters across a global passerine radiation

“…Further evidence for the link between morphological form and ecological function has also been shown in comparative studies within and between biological communities (Miles & Ricklefs, ; Pigot et al, ). However, these findings are seemingly in stark contrast to the results of recent analyses which suggest that ecological variables have limited power to explain morphological variation across taxonomically diverse sets of taxa (Felice, Tobias, Pigot, & Goswami, ; Navalón et al, ). To better understand these apparent discrepancies, and to improve our quantitative understanding of how well morphology reflects ecology more generally, we provide a comprehensive investigation of the relationships between ecological and morphological characters for a global avian radiation.…”

Functional performance of turtle humerus shape across an ecological adaptive landscape

“…; Jordan and Ryan ; Navalón et al. ); but how functional performance relates to organismal fitness can be difficult to quantify. Morphological traits can have complicated functional trade‐offs and similar organismal performance can be generated by divergent morphologies (“many‐to‐one mapping”; Lauder and Thomason ; Wainwright et al.…”

Digest: Evolution of shape and leverage of bird beaks reflects feeding ecology, but not as strongly as expected*

“…Navalón et al. () took up this challenge and examined the shape of the upper beak as well as the leverage of the main beak‐closing muscles on skulls of 176 bird species (Fig. ).…”

“…Overview of the analysis and results from Navalón et al. (). Feeding ecology was divided into (A) diet classes and (B) food acquisition methods, and their evolutionary correlation with two important characteristics of cranial morphology was tested: (C) the shape of the upper beak, and (E) the leverage (or gearing) of the main jaw closer muscles by the lower beak, for which high mechanical advantages (to efficiently generate high bite forces) are reached when the moment arm of the muscles’ input force is relatively high (E).…”

“…While shedding light on the role of trophic ecology on the macroevolution of the bird beak, Navalón et al. () also illustrate that the morphological demands of certain feeding styles, especially those relying on beak movements, remain unclear. Consequently, to better understand the observed eco‐morphological relationships, further biomechanical analyses of the cranial musculoskeletal system of birds are required (e.g., Dawson et al.…”