Ecological forecasts highlight opposing effects of long‐term climate change on population demography

Abstract

The multifaceted impacts of global climate change on biota challenge our understanding and capability of anticipating the long-term viability of wild populations, which is an emergent property of ecological systems. Using Bayesian integrated population modeling, sensitivity analyses, and ecological forecasting, we investigate how climate variability shapes the long-term population dynamics of a species highly sensitive to climate change: the emperor penguin (Aptenodytes forsteri). Leveraging a multi-decadal database from Pointe Géologie, East Antarctica, we assess penguin sensitivity to multiple environmental drivers and produce anticipatory projections of the emerging population trajectories under the noise of forecasted climatic changes. We found that receding fast ice during chick-rearing, leading to reduced commuting distances to open water, improves breeding success. Conversely, ocean warming and stronger winds negatively impact adult survival, possibly due to changes in Antarctic marine productivity. These contrasting effects of ocean warming and sea ice contractions on adult survival and breeding success, the most important contributors to the realized population growth rate, indicate opposing effects of climate change on penguins. Using forecasts, we explored how these opposing forces will jointly determine long-term emperor penguin population dynamics. We found that the increased breeding success linked to reductions in fast ice may buffer and delay population declines by over a decade. However, ocean warming and its likely repercussions to the food web and adult survival will ultimately drive population declines. While forecasting is well established in climate science, ecological forecasting faces distinct challenges, including shorter and less defined predictability horizons, greater stochasticity, and limited long-term data. Yet, forecasts can be used to understand and anticipate population responses, which is particularly valuable, given the urgent need to define proactive conservation plans. Here, forecasts reveal contrasting demographic impacts of sea ice loss and ocean warming on emperor penguins. Our approach, adaptable to other species and systems, highlights the value of anticipatory projections for disentangling and quantifying drivers of long-term population change.