Pleistocene climatic instability drove the historical distribution of forest islands in the northeastern Brazilian Atlantic Forest

Abstract

To investigate the past spatial dynamics of Atlantic Forest (AF) ‘island-like’ enclaves in northeastern Brazil, we employed ecological niche modeling (ENM) using a set of georeferenced records of 13 woody plant species. ENMs were constructed using the Ensemble forecasting approach and were projected into past climatic conditions for the last interglacial period (LIG, 120 kyr), last glacial maximum (LGM, 21 kyr), and the Middle Holocene (MH, 6 kyr). Our results suggest an expansion of wetter forests during the LGM into areas currently covered by the Caatinga seasonally dry woodlands, with recent retraction to the current distribution. Central AF islands located south of the São Francisco River underwent a different history compared to Northern AF islands north of this river: the former were mostly connected to coastal AF since the LIG (with a very recent separation), whereas the latter presented a more dynamic historical distribution. Results reveal contrasting spatiotemporal histories of forest instability and isolation across the various enclaves, supporting three main biogeographic hypotheses: i) moderate connectivity with coastal AF and a recent population bottleneck in the Araripe and Pernambuco/Paraíba enclaves, ii) low connectivity to, and long-term isolation from, other enclaves, as well as recent population bottleneck, in the northernmost North Ceará enclaves; and iii) high connectivity with coastal AF and recent population expansion in the southernmost Chapada Diamantina enclaves. Future comparative phylogeography studies will largely aid in assessing the herein proposed biogeographic scenarios during the highly dynamic recent history of the AF enclaves.