Abstract
Among birds, tropical montane species are likely to be among the most vulnerable to climate change, yet little is known about how climate drives their distributions, nor how to predict their likely responses to temperature increases. Correlative models of species’ environmental niches have been widely used to predict changes in distribution, but direct tests of the relationship between key variables, such as temperature, and species’ actual distributions are few. In the absence of historical data with which to compare observations and detect shifts, space-for-time substitutions, where warmer locations are used as analogues of future conditions, offer an opportunity to test for species’ responses to climate. We collected density data for rainforest birds across elevational gradients in northern and southern subregions within the Australian Wet Tropics (AWT). Using environmental optima calculated from elevational density profiles, we detected a significant elevational difference between the two regions in ten of 26 species. More species showed a positive (19 spp.) than negative (7 spp.) displacement, with a median difference of ∼80.6 m across the species analysed that is concordant with that expected due to latitudinal temperature differences (∼75.5 m). Models of temperature gradients derived from broad-scale climate surfaces showed comparable performance to those based on in-situ measurements, suggesting the former is sufficient for modeling impacts. These findings not only confirm temperature as an important factor driving elevational distributions of these species, but also suggest species will shift upslope to track their preferred environmental conditions. Our approach uses optima calculated from elevational density profiles, offering a data-efficient alternative to distribution limits for gauging climate constraints, and is sensitive enough to detect distribution shifts in this avifauna in response to temperature changes of as little as 0.4 degrees. We foresee important applications in the urgent task of detecting and monitoring impacts of climate change on montane tropical biodiversity.
Highlights
Evidence for warming of the global climate system is unequivocal, with widespread rises in air and sea temperatures likely driven by anthropogenic increases of atmospheric CO2 to concentrations well above pre-industrial levels [1]
While our sample includes many species from the diverse mid-slopes of the study area, differences are found among species in megatherm lowland environments. This tendency for lowland species to respond to increases in temperature to their upland counterparts may reflect a general tendency toward narrow thermal tolerance in tropical species [43], and has important repercussions for lowland biodiversity in a changing climate [6]
In some situations [5], predicted upslope shifts of lowland species driven by thermal tolerances could result in a process of lowland biotic attrition in the montane tropics [70]
Summary
Evidence for warming of the global climate system is unequivocal, with widespread rises in air and sea temperatures likely driven by anthropogenic increases of atmospheric CO2 to concentrations well above pre-industrial levels [1]. Extinctions due to the rapid rate of current change [2] may profoundly impact global patterns of biodiversity [3]. While the magnitude of measured temperature changes has been greater in high latitudes [1], steep gradients and narrow thermal tolerances may make tropical montane ecosystems vulnerable [4,5,6]. Climate change represents perhaps the most significant threat to tropical montane biodiversity [7,8], with substantial losses to extinction expected in coming centuries if warming remains unchecked [2,9]. There is an urgent need to validate projected impacts of climate change on montane tropical bird species [14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
