Incorporating fossil distribution data into Eld’s deer (Rucervus eldii, McClelland 1842) species distribution models improves their conservation prospects

Eld’s deer (Rucervus eldii, McClelland 1842) is an endangered cervid species endemic to Southeast Asia. Once widely distributed across seven countries within the Indo-Burma Biodiversity Hotspot, anthropogenic persecution and habitat destruction have led to a fragmented range with low population connectivity. As a result, the species’ conservation management efforts increasingly depend on translocations and reintroductions to suitable habitats. However, due to the species’ truncated modern distribution, it is possible that Eld’s deer no longer occupy their full environmental niche. Consequently, inferring habitat requirements of Eld’s deer from modern distributions alone may introduce bias into our perception of their environmental tolerances, and thus negatively influence conservation practices. To address this, we integrated fossil, historical and modern distribution data along with associated (palaeo)environmental records to construct species distribution models (SDMs). These models depict Eld’s deer environmental suitability under current and future climate scenarios (Shared Socioeconomic Pathway (SSP): SSP1–2.6 and SSP5–8.5). Although our results suggest that some extant populations may currently persist in suboptimal habitats, by incorporating fossil data, we gain a more complete understanding of the species’ environmental tolerances, offering a more optimistic outlook for their persistence under future climate change. This study also identifies potential reintroduction areas and highlights the importance and value of integrating fossil records into species distribution modelling for conservation purposes.