Brain Size and Life History Interact to Predict Urban Tolerance in Birds

Ferran Sayol,Alex L Pigot,Daniel Sol

doi:10.3389/fevo.2020.00058

Abstract

Urbanization is a major driver of local biodiversity losses, but the traits that determine whether species are able to tolerate urban environments remain poorly understood. Theory suggests that a larger brain should provide higher tolerance to urbanization by enhancing behavioral flexibility to cope with novel challenges. However, assembling empirical evidence for a link between brain size and tolerance to urbanization has proven to be difficult, perhaps because the effect of the brain interacts with life history to influence persistence in urban environments. Here, we provide a global-scale assessment of the role of brain size on urban tolerance, combining quantitative estimations of urban tolerance with detailed information on brain size, life history and ecology for 629 avian species across 27 cities. Our analysis confirms the expected positive association between brain size and urban tolerance, but shows that the relationship is more complex than previously shown. While a large relative brain size generally increases urban tolerance, species with small brains can still attain high success in urban environments if they spread the risk of reproduction in multiple events (i.e. have a low brood value). These alternative strategies, although uncommon in natural conditions, seem to be favored in urban environments, fundamentally restructuring the composition of urban communities. Thus, our results support the notion that brain size mediates tolerance to urbanization, but also shows that there are alternative ways of exploiting urban environments. Our findings reconcile previous conflicting results regarding the effect of brain size on urban tolerance, and provide the basis for improved predictions of the responses of organisms to increasing urbanization over the coming decades.

Highlights

Cities are home to almost 4 billion people and over the coming decades their populations and geographic footprint will continue to swell (Seto et al, 2011, 2012)
We found that relative brain size is positively related to urban tolerance (Posterior mean or ß, with 95% confidence intervals = 0.450 [0.115–0.818], pMCMC = 0.012), when included as a single predictor
In the model including brood value, the main effect of relative brain size was no longer a significant predictor of urban tolerance. This in part reflects the existence of a weak negative association between brain size and brood value, so that species with relatively large brains were generally associated with low brood values (ß = −0.083 [−0.129 to −0.033], pMCMC < 0.001)

Summary

Introduction

Cities are home to almost 4 billion people and over the coming decades their populations and geographic footprint will continue to swell (Seto et al, 2011, 2012). Among the different explanations for why some animals are able to exploit urban environments, one that has recently received greater attention is the cognitive buffer hypothesis (Allman et al, 1993; Sol, 2009). According to this hypothesis, a large brain should enhance persistence in novel environments by facilitating the construction of behavioral responses to new challenges, an idea supported by growing evidence (Sol et al, 2005, 2008; Sayol et al, 2016b; Fristoe et al, 2017). Whether large brain size predicts success in urban environments remains controversial (Table 1), with early support for this hypothesis (Møller, 2009; Maklakov et al, 2011, 2013), challenged by later studies (Evans et al, 2011; Sol et al, 2014; Dale et al, 2015; Møller and Erritzøe, 2015), only to be re-affirmed by more recent analysis (Callaghan et al, 2019)

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Results

Conclusion