Long-term changes in populations of rainforest birds in the Australia Wet Tropics bioregion: A climate-driven biodiversity emergency

Abstract

Many authors have suggested that the vulnerability of montane biodiversity to climate change worldwide is significantly higher than in most other ecosystems. Despite the extensive variety of studies predicting severe impacts of climate change globally, few studies have empirically validated the predicted changes in distribution and population density. Here, we used 17 years (2000–2016) of standardised bird monitoring across latitudinal/elevational gradients in the rainforest of the Australian Wet Tropics World Heritage Area to assess changes in local abundance and elevational distribution. We used relative abundance in 1977 surveys across 114 sites ranging from 0-1500m above sea level and utilised a trend analysis approach (TRIM) to investigate elevational shifts in abundance of 42 species. The local abundance of most mid and high elevation species has declined at the lower edges of their distribution by >40% while lowland species increased by up to 190% into higher elevation areas. Upland-specialised species and regional endemics have undergone dramatic population declines of almost 50%. The “Outstanding Universal Value” of the Australian Wet Tropics World Heritage Area, one of the most irreplaceable biodiversity hotspots on Earth, is rapidly degrading. These observed impacts are likely to be similar in many tropical montane ecosystems globally.

Predicted alteration of vertebrate communities in response to climate‐induced elevational shifts

“…Our findings align with those predicted from uphill shifts, showing a classic example of the "escalator to extinction" (Marris, 2007;Urban, 2018). As evidenced in this study, the impact of climate than their counterparts at lower elevations (Freeman, Scholer, et al, 2018;Williams & de la Fuente, 2021). Our results are in accordance with projected impacts of climate change in mountain ecosystems (Mamantov et al, 2021;Manes et al, 2021;Williams et al, 2003), warning of severe deterioration of montane communities, which host unique ecosystem services (Korner & Spehn, 2019), and a disproportionate amount of global biodiversity (Jetz et al, 2004;Quintero & Jetz, 2018).…”

“…As environmental conditions change rapidly due to climate change, species must adapt, move or face extinction (Berg et al, 2010). Consistent with this, climate change has induced distributional shifts (Chen et al, 2011;Freeman, Lee-Yaw, et al, 2018;Parmesan & Yohe, 2003) and local extinctions (Freeman, Lee-Yaw, et al, 2018;Iknayan & Beissinger, 2018;Sinervo et al, 2010) of many species worldwide, with the greatest observed shift in distribution associated with the interaction between global warming (Chen et al, 2011) and species' environmental constraints (Williams & de la Fuente, 2021). Evidence demonstrates a broad global pattern of uphill and poleward distributional shifts (Hickling et al, 2006;Parmesan et al, 1999;Tiberti et al, 2021), warning us of potential disruptions of ecological dynamics and processes (Johnson et al, 2010;Post et al, 2009).…”

“…Species in montane ecosystems can show a variety of responses to climate change (Mccain & King, 2014;Tingley et al, 2012). The potential for species to adapt or even move downhill in elevation has been previously reported based on demographic responses and changes in occupancy (Chen et al, 2011;Moritz et al, 2008;Neate-Clegg et al, 2021;Tingley et al, 2012;Williams & de la Fuente, 2021). However, the underlying mechanisms for species heterogeneous range shifts and demographic fluctuations could also be related to lags in response to changes in the environmental conditions (Alexander et al, 2018;Bertrand et al, 2011;Fordham et al, 2016;La Sorte & Jetz, 2012;Lu et al, 2021), rather than species adaptability to climate change.…”

“…Evidence demonstrates a broad global pattern of uphill and poleward distributional shifts (Hickling et al, 2006;Parmesan et al, 1999;Tiberti et al, 2021), warning us of potential disruptions of ecological dynamics and processes (Johnson et al, 2010;Post et al, 2009). Climate-induced elevational shifts have been especially marked in tropical montane ecosystems (Chen et al, 2009;Freeman & Freeman, 2014;Neate-Clegg et al, 2021), resulting in upland specialist tropical species undergoing substantial declines in abundance (Freeman, Scholer, et al, 2018;Pounds et al, 1999;Williams & de la Fuente, 2021) and local extinction at high altitudes (Freeman & Freeman, 2014).…”

“…In open communities, under climatic-induced geographical shift, dispersal differences among species could dissolve existing species interactions, eliminating some processes and creating new ones (Ackerly, 2003;Schweiger et al, 2008). Disrupted and novel interactions will likely alter abundances, distributions and extinction probabilities of species (Carpenter et al, 2008;Deutsch et al, 2008;Williams & de la Fuente, 2021). In this regard, metacommunity dynamics will be dependent on dispersal restrictions under climate change (Gilman et al, 2010), causing extinctions of low-dispersal species and favouring the range expansion of high-dispersal species.…”