Abiotic niche predictors of long-term trends in body mass and survival of Eastern Himalayan birds

Abstract

AbstractClimate change and habitat degradation are two of the greatest threats to tropical biodiversity today. In addition to their independent effects, habitat degradation compounds the impacts of climate change by creating habitats with novel abiotic characteristics (typically hotter, drier and more variable). Tropical species are often microhabitat and microclimate specialists occupying distinct temperature and humidity niches. How species’ abiotic niches affect their responses to the joint impacts of climate change and habitat degradation remains poorly understood, especially in terms of changes in phenotype and demographic vital rates. Using an 11-year mark-recapture dataset and temperature-humidity measurements from primary and selectively logged forest from 2000m in the Eastern Himalayas, we investigate how the abiotic (temperature-humidity) niche sizes of populations of species in primary forest and abiotic niche overlaps between populations in primary and logged forest predicted body mass and survival trends over time for populations in each habitat. Our results show that logged forest is hotter and drier than primary forest, and the arthropod community shows dramatic shifts in composition upon selective logging. In understorey insectivores, we find that body masses appear to be declining over time in logged, but not in primary forest. Further, across species, we report a positive relationship between the size of the primary forest niche and body mass trends over time in primary forest but not in logged forest. The degree of dissimilarity between species-specific primary and logged forest niches was strongly and negatively correlated with survival trends in logged forest. Here, we show that temperature-humidity niche shifts in response to anthropogenic habitat modification can impact demographic vital rates crucial for population persistence. This work has the potential to inform prompt, targeted conservation efforts toward species that are the most threatened in a warmer and more degraded world.