Ecological Correlates of Elevational Range Shifts in Tropical Birds

Montague H C Neate-Clegg,William D Newmark,Joseph A Tobias,Samuel E I Jones,Çaǧan H Şekercioǧlu

doi:10.3389/fevo.2021.621749

Abstract

Globally, birds have been shown to respond to climate change by shifting their elevational distributions. This phenomenon is especially prevalent in the tropics, where elevational gradients are often hotspots of diversity and endemism. Empirical evidence has suggested that elevational range shifts are far from uniform across species, varying greatly in the direction (upslope vs. downslope) and rate of change (speed of elevational shift). However, little is known about the drivers of these variable responses to climate change, limiting our ability to accurately project changes in the future. Here, we compile empirical estimates of elevational shift rates (m/yr) for 421 bird species from eight study sites across the tropics. On average, species shifted their mean elevations upslope by 1.63 ± 0.30 m/yr, their upper limits by 1.62 m ± 0.38 m/yr, and their lower limits by 2.81 ± 0.42 m/yr. Upslope shift rates increased in smaller-bodied, less territorial species, whereas larger species were more likely to shift downslope. When considering absolute shift rates, rates were fastest for species with high dispersal ability, low foraging strata, and wide elevational ranges. Our results indicate that elevational shift rates are associated with species’ traits, particularly body size, dispersal ability, and territoriality. However, these effects vary substantially across sites, suggesting that responses of tropical montane bird communities to climate change are complex and best predicted within the local or regional context.

Highlights

Both biodiversity and endemism are associated with elevational gradients in the tropics (Myers et al, 2000; Orme et al, 2005; Quintero and Jetz, 2018)
We used a meta-analysis of range-shift data from across the tropics to explore the ecological predictors of elevational range shifts in tropical forest birds
We show that species distributed along eight tropical elevational gradients have, on average, shifted upslope at a rate of 1.6 m/yr, but that rates and directions were highly variable

Summary

Introduction

Both biodiversity and endemism are associated with elevational gradients in the tropics (Myers et al, 2000; Orme et al, 2005; Quintero and Jetz, 2018). Climate change imperils many species that inhabit narrow elevational gradients (Sekercioglu et al, 2008), threatening to reduce their elevational ranges and eventually drive them to extirpation or extinction (Pounds et al, 1999; Freeman et al, 2018a,b) Despite this threat, the Elevational Shifts in Tropical Birds responses of tropical montane species to climate change vary substantially, but the ecological drivers of this variation remain unresolved. While most species tend to shift upslope as predicted, between a third and a fifth of species shift downslope (Forero-Medina et al, 2011b; Freeman and Class Freeman, 2014; Freeman et al, 2018b; Mamantov et al, 2021) Such variation suggests that elevational shifts are complex and site or species-specific (Fadrique et al, 2018), and that species are not tracking shifting climate envelopes

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