Accurate species distribution models: minimum required number of specimen records in the Caatinga biome.

Species distribution models (SDMs) are one of the most widely used tools to predict areas with potential for occurrence of native, invasive and endangered species, based on current and future environmenal and climate conditions. Despite their global use, evaluating the accuracy of SDMs based only on presence records is still a challenge. The performance of models depends on the sample size and species prevalence. Recently, studies to model the distribution of species in the Caatinga biome in Northeast Brazil have gained force, raising the question about the minimum number of presence records adjusted to different prevalences that are necessary to generate accurate SDMs. In this context, the objective of this study was to indicate minimum numbers of presence records for species with different prevalences in the Caatinga biome to obtain accurate SDMs. For that purpose, we used a method involving simulated species and performed repeated evaluations of the models' performance in function of the sample size and prevalence. The results indicated that for this approach in the Caatinga biome, the minimum required numbers of specimen records were 17 and 30 for species with narrow and widespread distributions, respectively.

Impacts of climate change on the potential distribution of epiphytic cacti in the Caatinga biome, Brazil.

The Caatinga biome is the largest dry tropical forest region in South America as well as one of the most vulnerable regions in the world to the climate changes forecast for this century. Climate forecasts for the biome include increased air temperature, reduced rainfall and aridization. This biome does not have a homogeneous landscape; instead it has several rainforest enclaves. This article describes a study to model the potential distribution of four epiphytic cactus species (Epiphyllum phyllanthus (L.) Haw., Rhipsalis floccosa Salm-Dyck ex Pfeiff., Rhipsalis lindbergiana K. Schum and Rhipsalis russellii Britton & Rose.) in the biome under future climate scenarios and traces out a prognosis for the enclaves and the biome. For that purpose, we used the MaxEnt modeling method, considering two future time intervals (2041-2060 and 2061-2080) and the interval 1961-1990 for the current situation, with the RCP4.5 and 8.5 scenarios. The projections for future potential distribution showed a spatial contractions greater than 88% found in the areas of high potential presence for the target species throughout the biome and in all the scenarios. The results strengthen the expectation of aridization in the Caatinga biome, with the loss or shrinkage of rainforest enclaves as time progresses.