Using Holocene fossils to model the future: Distribution of climate suitability for tuatara, the last rhynchocephalian

Aim Correlative species distribution models (SDMs) are typically trained using only the contemporary distribution of species; however, recent records might reflect an incomplete description of a species' niche, limiting the reliability of predictions. SDMs linking fossil records have the potential to improve conservation decisions under human-induced climate change. Here, we built SDMs using presence records from contemporary and Holocene records to enable estimations of climatically suitable area under current and future climate scenarios. Location Aotearoa New Zealand Taxon Tuatara, Sphenodon punctatus Methods For an evolutionary relict found in Aotearoa New Zealand, the tuatara (Sphenodon punctatus), we built SDMs using presence records from contemporary and Holocene records to estimate climatically suitable area under current and future climate scenarios. We also use our detailed knowledge of the Holocene distribution and remnant populations to examine niche shifts following the arrival of humans and associated introduction of mammalian predators. To build SDMs, we use presence records from four sources: (a) remnant populations, (b) radiocarbon-dated fossil deposits from the Holocene, (c) other fossil deposits containing tuatara bones of Holocene age and iv) islands from which tuatara are known or highly likely to have become extinct. Results We found shifts in the niche of tuatara due to niche unfilling. Incorporating locations of Holocene deposits and/or all past locations in SDMs led to larger areas of climatically suitable area being identified compared to SDMs derived from remnant populations only. Using all presence records, under climate change projections for 2090, climatically suitable area increased slightly. However, many areas retain potential as translocation sites (e.g. northern South Island), some areas become unsuitable (e.g. inland Canterbury) and/or involve extrapolation into novel climates (e.g. Northland). Main Conclusion SDMs incorporating locations of Holocene deposits and/or all past locations identified areas of critical habitat for tuatara under current and future climate scenarios, that would not have been identified using contemporary occurrences only. Our results highlight the need to consider past locations when assessing habitat suitability for conservation translocations, both for tuatara and other relict species.

Automated summary

SDMs incorporating Holocene records and all past locations can more accurately estimate the climatically suitable area for tuatara, showing a larger suitable area compared to using contemporary records only, and indicating niche shifts in tuatara over time.