Too much of a good thing? Supplementing current species observations with fossil data to assess climate change vulnerability via ecological niche models

Ecological niche models (ENMs) are a powerful tool in ecological research and conservation planning. Since ENMs provide probability maps of suitable areas under environmental change, they may assist in designing conservation actions and addressing conservation priorities. However, ENMs are usually implemented by learning the species climatic preferences from their current geographic distribution, which leaves them vulnerable to the issue of niche truncation, as it comes with non-climatic limits to the current species distribution as posed by anthropic activities and settlements, and competition avoidance. These problems might be alleviated by the inclusion of fossil occurrences, which refer to moments during species existence when such limits were absent or distributed differently. By stacking species occurrences from different time moments is conceivable that a larger fraction of the species fundamental niche is thence explored. Here, we combined current and fossil occurrence data for 38 medium-large mammal species of conservation concern in order to assess the influence of the fossil record inclusion on ENM predictions under future climate change scenarios. We found that ignoring or including fossil data yields consistent trends in terms of predicted range increase/decrease. Yet, although adding fossil data invariably results in increased niche width, estimates of range change improved for almost a half only of the species pool. These results suggest that most species might currently be in non-equilibrium with their environment, and that the inclusion of fossil data may be crucial to the better understanding of species climatic requirements, hence for designing more effective conservation strategies.