Climate change is an increasing threat to global biodiversity but its predicted effects in the tropics are still poorly understood. The Eastern Himalayas are a global biodiversity hotspot; in particular, this region has the highest global passerine bird density. They are also a relatively understudied region. Moreover, it is thought that climate change will disproportionately affect montane regions. The bird community in the Eastern Himalayas is altitudinally stratified, with competitive species interactions hypothesized to have played a major role in diversification and current spatial distributional patterns. We conducted three summers of fieldwork in the region, and used the results in a niche modelling framework to estimate the effects of climate change on the distribution of individual species under four different emissions scenarios. We also used a simulation model to estimate the effects of species interactions on closely related species pairs in limiting each other’s spatial ranges.
Results/Conclusions
We found that on average, species are expected to experience range contractions, with the largest predicted contractions coming under the most pessimistic climate scenarios. Several species are expected to lose suitable habitat entirely, including some thought to be of current conservation concern by the IUCN. Individual species are predicted to respond to climate change in different ways depending on whether they are more sensitive to changes in precipitation or temperature; species tracking precipitation are more likely to move downslope and species tracking temperature are more likely to move upslope. Overall, species that are currently located at higher altitudes, and species that are projected to move upslope, are projected to experience the most severe range contractions due to climate change. Species interactions are expected to further exacerbate range contractions for some species, as their ranges will move into areas currently occupied by competitors; this may decrease the amount of projected available habitat by over 50% for some species, including at least one thought to be of conservation concern by the IUCN (Rusty-bellied Shortwing, Brachypteryx hyperythra). These results have important implications for our understanding of the threat climate change poses to high-diversity tropical areas. Additionally, these results will help inform future conservation action in the region, including by allowing us to identify regions that are priorities for future conservation action as the current system of protected areas does not account for the possibility of shifting species’ ranges due to climate change.