Allee effects mediate the impact of land-use change on the thermal niche of social species

Abstract

Land-use change not only affects habitat availability, it can also reduce population density and limit opportunities for interactions with conspecifics, further influencing species resilience to environmental challenges. For social species whose conspecific interactions are typically cooperative in nature, little is known about how land-use change influences demography and social behavior, and how this interaction impacts a species climatic niche. Here, we develop a spatially explicit, individual-based model to explore how land-use changes influence population size and niche width in social organisms through the Allee effect, the positive impact of higher population density on individual fitness. We then empirically test key model predictions by studying the distribution and cooperative behavior of burying beetles (Nicrophorus nepalensis) along elevational gradients in Taiwan. In support of our model predictions, we find that beetle densities are lower in areas of greater land-use change, making it harder for individuals in these hotter environments to form cooperative groups to compete against blowflies, their primary interspecific competitor. Consequently, the beetles lower distributional boundary is higher in areas with greater land-use change, indicating that the beetles thermal niche is reduced via Allee effects in human-altered landscapes. Ultimately, land-use change not only reduces habitat availability, it also shrinks the thermal niche of social species, making them more vulnerable to climate change.