Geographic variation in body size and plumage colour according to diet composition in a nocturnal raptor

Andrea Romano,Alexandre Roulin,Robin Séchaud

doi:10.1111/jav.02716

Andrea Romano, Alexandre Roulin + Show 1 more

Open Access

https://doi.org/10.1111/jav.02716

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Abstract

Predator–prey interactions are amongst the strongest selective forces that promote the evolution of local phenotypes in both predators and prey. However, intraspecific spatial covariation in phenotypic traits between predators and prey has been rarely investigated, especially at a large geographic scale. Here, we studied the covariation between prey composition and some phenotypic traits, such as wing length, bill length and plumage colour, of a widely‐distributed nocturnal predator, the western barn owl Tyto alba. By using 3100 specimens collected across its entire range of distribution, spanning from Europe to Middle East and Africa, we showed that wing length positively covaries with prey size, but not with taxonomic composition. This finding suggests that larger prey might have selected for larger body size and/or that larger individuals might be more selective in hunting large prey. In addition, we also found that paler‐plumaged populations generally hunt larger prey. Paler barn owls might be thus better specialized in capturing averagely larger prey and/or mainly hunt in habitats where larger prey are more abundant. In addition, considering that paler individuals are generally larger than brownish ones, it is possible that paler plumage colour might have evolved as a by‐product of selection towards a large body size, which in turn have emerged in response to prey size composition. However, irrespectively of the direction of causality and the phenotypic target of selection, we showed that predator–prey interactions can affect spatial phenotypic variation by promoting the evolution of local adaptations.

Highlights

Interactions between prey and predators are amongst the major selective forces that drive a diverse suite of functional phenotypes in both counterparts (Kerfoot and Sih 1987, Tollrian and Harvell 1999)
One of the main results found in the present study on a very large geographic scale was that populations of the western barn owl that had longer wings hunted larger prey compared to those showing on averagely smaller wings. This finding is in line with most of interspecific comparative studies (Vézina 1985, Radloff and Du Toit 2004, Owen-Smith and Mills 2008, Costa 2009, but see Török 1993) and within-population analyses (Simpfendorfer et al 2001, Ingram et al 2011) showing a predator–prey size allometric scaling, and suggests that large individuals are able to exploit a larger fraction of the encountered prey, including large ones
This pattern can be interpreted as an adaptation of barn owl body size for an efficient use of the available sources of food

Summary

Introduction

Interactions between prey and predators are amongst the major selective forces that drive a diverse suite of functional phenotypes in both counterparts (Kerfoot and Sih 1987, Tollrian and Harvell 1999). Larger species usually live in larger home and geographic ranges than smaller ones, potentially encountering a wider variety of prey According to these premises, a positive association between a predator’s body size and its diet niche breadth is expected (Gittleman 1985, Scharf et al 2000). A positive association between a predator’s body size and its diet niche breadth is expected (Gittleman 1985, Scharf et al 2000) Such an allometric scaling in the relationships between predator size and prey size and diversity is a crucial aspect of food web and metabolic theories (Emmerson and Raffaelli 2004, Brose et al 2006b, Otto et al 2007, Petchey and Dunne 2012, Kalinkat et al 2013)

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