Temperature niche composition change inside and outside protected areas under climate warming.

Conservation of biodiversity relies heavily on protected areas but their role and effectiveness under warming climate is still debated. Here, we estimated the climate-driven changes in the temperature niche compositions of bird communities inside and outside protected areas in southern Canada. We expected that communities inside protected areas include a higher proportion of cold-dwelling species than communities outside protected areas. Secondly, we expected that the communities change towards dominance of warm-dwelling species slower inside protected areas than outside. To study community changes, we used large-scale and long-term data from the Breeding Bird Survey of Canada from 1997-2019. To describe the temperature niche compositions of bird communities, we calculated the community temperature index (CTI) annually for each community inside and outside protected areas. Generally, warm-dwelling species dominate communities with high CTI values. We modeled temporal changes in CTI as a function of protection status using linear mixed effect models. We also determined which species contributed most to the temporal changes in CTI using a jackknife approach. As anticipated, CTI was lower inside protected areas compared to outside. However, contrary to our expectation, CTI increased faster over time inside than outside protected areas, and the warm-dwelling species contributed most to CTI change inside protected areas. These results highlight the ubiquitous impacts of climate warming. Currently, protected areas can aid cold-dwelling species by providing suitable habitats, but as climate warms, the communities' temperature compositions inside protected areas quickly begin to resemble those outside protected areas, suggesting that protected areas delay the impacts of climate warming on cold-dwelling species. This article is protected by copyright. All rights reserved.