Revisiting the historical distribution of Seasonally Dry Tropical Forests: new insights based on palaeodistribution modelling and palynological evidencegeb

Abstract

Aim To investigate the potential distribution of Seasonally Dry Tropical Forests (SDTFs) during the Quaternary climatic fluctuations; to reassess the formerly proposed 'Pleistocenic arc hypothesis' (PAH); and to identify historically stable and unstable areas of SDTF distributions in the light of palaeodistribution modelling. Location SDTFs in lowland cis-Andean eastern-central South America. MethodsWe first developed georeferenced maps depicting the current distributional extent of SDTFs under two distinct definitions (narrow and broad). We then generated occurrence datasets, which were used with current and past bioclimatic variables to predict SDTF occurrence by implementing the maximum entropy machine-learning algorithm. We obtained historical stability maps by overlapping the presence/absence projections of each of three climatic scenarios [current, 6 kyr bp during the Holocene, and 21 kyr bp during the Last Glacial Maximum (LGM)]. Finally, we checked the consistencies of the model prediction with qualitative comparisons of vegetation types inferred from available fossil pollen records. Results The present-day SDTF distribution is disjunct, but we provide evidence that it was even more disjunct during the LGM. Reconstructions support a progressive southward and eastward expansion of SDTFs on a continental scale since the LGM. No significant expansion of SDTFs into the Amazon Basin was detected. Areas of presumed long-term stability are identified and confirmed (the three nuclear regions, Caatinga, Misiones and Piedmont, plus the Chiquitano region), and these possibly acted as current and historical refugial areas. Main conclusions The LGM climate was probably too dry and cold to support large tracts of SDTF, which were restricted to climatically favourable areas relative to the present day (in contrast with the PAH, as it was originally conceived). Expansions of SDTFs are proposed to have occupied the southern portion of Caatinga nucleus more recently during the early-middle Holocene transition. We propose an alternative scenario amenable to further testing of an earlier SDTF expansion (either at the Lower Pleistocene or the Tertiary), followed by fragmentation in the LGM and secondary expansion in the Holocene. The stability maps were used to generate specific genetic predictions at both continental and regional scales (stable areas are expected to have higher genetic diversity and endemism levels than adjacent unstable areas) that can be used to direct field sampling to cover both stable (predicted refugia) and unstable (recently colonized) areas. Lastly, we discuss the possibility that SDTFs may experience future expansion under changing climate scenarios and that both stable and unstable areas should be prioritized by conservation initiatives.

Contrasting effects of sampling scale on insect herbivores distribution in response to canopy structure

“…Rio Doce river basin may be covered with a particularly insect species-poor forest due to its ecological young age. Geological studies suggest the whole region was broadly covered by xeric ecosystems and tropical dry forests no later than 4 000 years ago during the Holocene (Overloop 1981, Werneck et al 2011, which contributed to the origin of the lakes that define enormously this landscape (Pflug 1969, Meis & Monteiro 1979, Meis & Tundisi 1986, Perônico & Castro 2008. Still, regardless fast and recent climatic and, consequently, ecological shifting, the relative abundance of herbivore taxa followed expected trends found in some Neotropical canopies (Ribeiro 2003).…”

Phylogeographic model selection leads to insight into the evolutionary history of four-eyed frogs

“…(84). The study area encompasses current and putative past Caatinga distributions according to previous studies (47,48). We selected eight uncorrelated variables (Pearson correlation <0.7) downloaded from Bioclim at 2.5 arc minutes resolution: mean diurnal range, isothermality, temperature seasonality, annual precipitation, precipitation of driest month, precipitation seasonality, precipitation of warmest quarter, and precipitation of coldest quarter.…”

“…45], and other evidence favoring an older (Tertiary) fragmentation (46). Environmental niche modeling results in contrasting maps ranging from a largely continuous to a fragmented Caatinga, depending on the approach used (47,48). Regardless of the broader continental trends of the SDTFs, there is abundant geologic evidence that the Caatinga has been recurrently invaded (and at least partially replaced) by mesic forest throughout its history (49,50).…”

First avifaunal survey of a Cerrado dry forest enclave on the right bank of the São Francisco River, Minas Gerais, Brazil, with insights on geographic variation of some species

“…Seasonally dry tropical forests (hereafter SDTFs) present a circum-Amazonian distribution in South America and have been the main focus of many recent biogeographic and conservation studies (e.g., Prado & Gibbs, 1993;Espírito-Santo et al, 2009;Pennington et al, 2000Pennington et al, , 2006Pennington et al, , 2009Zanella, 2010;Werneck, 2011;Werneck et al, 2011;Santos et al, 2012;Arruda et al, 2013;DryFlor, 2016). These forests are usually associated with fertile soils and with climates marked by highly seasonal rainfall with a severe dry season of three to six months, when most of the vegetation is leafless (Pennington et al, 2006;DryFlor, 2016).…”