Projected climate change threatens Himalayan brown bear habitat more than human land use

Abstract

Climate change and land use change jointly are the largest drivers of population declines, range contraction and extinction for many species across the globe. Wide‐ranging and large‐bodied species are especially vulnerable to habitat loss and fragmentation due to their typically low population densities, reflecting their need for extensive and connected habitats. We used the multi‐scale Random Forests machine learning algorithm to identify factors driving the habitat selection and future changes in habitat of Himalayan brown bear, an iconic wide‐ranging and large‐bodied species of high conservation interest, across a range of spatial scales. Habitat selection of brown bears was scale‐dependent, with most variables selected at broad scales. Climatic variables such as maximum temperature of coldest month, minimum temperature of warmest month and the potential evapotranspiration of wettest quarter strongly influenced habitat selection of brown bears. Future projections indicate a strong difference between the high and low emission scenarios. Alarmingly, our model suggests that high emission scenarios, with or without land use change, may result in a decline of brown bear habitat of >90% by the end of the century. In contrast, low emission scenarios are projected to reduce brown bear habitat by <23%, with much of the species range shifting to higher elevations. This study provides an integrative understanding of scale‐dependent variables in brown bear habitat selection, providing critical information for prioritizing areas for habitat management and conservation. Most importantly, our future projections imply that traditional conservation efforts, such as in situ conservation, will not be sufficient to protect the species without climate change mitigation. The incorporation of climate change mitigation and adaptation in conservation strategies will be one of the most pressing priorities in biodiversity conservation in this region.

Using machine learning to predict habitat suitability of sloth bears at multiple spatial scales

“…Our results are consistent with similar studies arguing that habitat selection measured at one specific scale may be insufficient to predict that selection at another scale (Mayor et al 2009). Similar studies for brown bears (Martin et al 2012;Sánchez et al 2014); Dar et al 2021) and other species (Shirk 2012;Shirk et al 2014;Wan et al 2017;Klaassen and Broekhuis 2018) also support the scale-dependent habitat selection. Consistent with these studies, our results indicate that habitat selection occurs across the range of scales for sloth bears, thus supporting our hypothesis of scale-dependent habitat selection in sloth bears.…”

“…Habitat features such as forest cover, terrain heterogeneity, and human population density were reported to be influential on a large scale (Puri et al 2015). A similar multi-scale distribution assessment using the random forest algorithm was attempted for Himalayan brown bears (Ursus arctos isabellinus) across their range in Himalayas (Dar et al 2021). The study showed that habitat selection in brown bears was scale-dependent and brown bears perceived the habitat features across multiple spatial scales.…”

“…In another similar study using resource selection functions (RSFs), the habitat selection by grizzly bears was also found to be scale-dependent (Ciarniello et al 2007). The importance of multi-scale assessment in determining the species-habitat relationships has been demonstrated in a wide range of species (e.g., Wan et al 2017;Klaassen and Broekhuis 2018;Khosravi et al 2019;Atzeni et al 2020;Rather et al 2020bRather et al , 2020cAsh et al 2021;Dar et al 2021).…”

Predicted declines in suitable habitat for greater one‐horned rhinoceros (Rhinoceros unicornis) under future climate and land use change scenarios

“…The reason behind the comparatively less contribution of land use change in predicted habitat decline is possibly because a majority of alluvial floodplain has already been converted into croplands. Similar studies conducted in India and Nepal for Asian elephant and Himalayan brown bear also suggested that the likely effects of climate change on habitat decline is greater than human land use changes (Dar et al, 2021 ; Kanagaraj et al, 2019 ).…”

“…Our ensemble approach identified suitable rhinoceros habitat that was mainly concentrated in the central and western lowland of Nepal, indicating that its distribution was constrained by topographic variables. Suitable habitat ranges of many terrestrial species have shifted toward higher elevations in response to changing climate (Chen et al, 2011 ; Dar et al, 2021 ; Moritz et al, 2008 ). Rhinoceros habitat suitability is limited by topographic factors given that slope contributed strongly to our models (Figure 4e ).…”