1 INTRODUCTION
Changes in climatic conditions are periodic and common in nature in different regions of the planet. They correspond to a natural cyclic process involving warming, cooling and intense geological activities of the Earth that promote various phenomena and effects, causing changes in biological systems and ecological interrelations (Oliveira, Carneiro, Vecchia, & Baptista, 2017). However, anthropogenic actions of the last 200 years have contributed to harmful conditions, changing particle/gas concentrations in the atmosphere with the intensification of land use and occupation (Oliveira et al., 2017; IPCC, 2018), and accelerating the speed of environmental processes to the point of preventing species from adapting or finding more suitable places to live.
The increase in the average global surface temperature is one of the main concerns of the scientific community in view of its immediately noticeable effects and relation with the biosphere in general. During the last century, the increase recorded was of approximately 0.87 °C above pre-industrial levels (IPCC, 2014) and if the temperature continues to rise at the current rate, the increase is estimated to reach 1.5 °C between 2030 and 2052 (IPCC, 2018). The expected average increase in South America is 4 °C, indicating a higher frequency of extreme events in Brazil, such as floods and heat waves (Marengo, 2005). Regional models indicate that by the end of the 21stcentury, the most intense effects will occur in the tropical region, specifically in the Amazon and Northeast of Brazil (Nobre, Sampaio, & Salazar, 2008).
Climate and geological transformations have triggered adaptive processes in biological communities, leading to their evolution, development, diversification, dispersion and extinction throughout the history of lineages (Costa, Veloso Filho, Aquino, & Castro, 2012). It is particularly important to be aware of their effects on biodiversity, because of the associated changes in distribution, phenology, migration calendar, nesting success, and population sizes of species. Thus, the response of biodiversity to climate change has become a very fruitful field for research (Hughes, 2000; McCarty, 2001; Walther et al., 2002; De Marco Junior & Siqueira, 2009; Walther, Berger, & Sykes, 2005; Bellard, Bertelsmeier, Leadley, Thuiller, & Courchamp, 2012), including studies with animal (Crick, 2004; Ribeiro, Sales, & Loyola, 2018; Miranda, Imperatriz-Fonseca, & Giannini, 2019) and plant (Siqueira & Durigan, 2007; Simões, Zappi, Costa, Oliveira, & Aona, 2019) assemblages. Biological interaction with climate is easily observed in geophysical patterns of vegetation distribution, reflecting different bioclimatic zones (Salazar, Nobre, & Oyama, 2007). Within the South American climate ranges, rainforest and savanna are the predominant biomes. They are also largely deforested, what has led to worsening climate change because the removal of vegetation cover promotes a warmer and drier regional climate (Nobre et al., 2008). However, although some evidence of current extinctions is correlated with climate change, studies suggest that climate phenomena could outweigh habitat destruction as the greatest global threat to biodiversity in the coming decades (Pereira et al., 2010; Bellard et al., 2012).
Studies on Quaternary climate fluctuations and vegetation in Brazil confirm that successive expansions and retractions occurred between forests and savannas (Silva; Bates, 2002), the main habitat typologies in Brazil. Cerrado is the largest forest savanna in South America, covering 21% of the country’s land area and extending marginally into Paraguay and Bolivia, behind only the Amazon Forest in terms of extension (CI, 2019). Research in tropical South America has shown Brazil as a region where significant amounts of forests are converted into non-forest areas as a result of global warming (Ledru, 2002; Sanaiotti, Martinelli, Victoria, Trumbore, & Camargo, 2002; Salazar et al., 2007). Field observations and numerical models also indicate loss of tropical forest cover (Soares-Filho et al., 2006; Vale, Cohn-Haft, Bergen, & Pimm, 2008; Rochedo et al., 2018; Gomes, Vieira, Salomão, & Steege, 2019), replaced by savannas (Salazar et al., 2007); this potential reorganization of the distribution of biodiversity can affect the structure, dynamics and functioning of ecosystems and their respective contributions (Gallagher, Hughes, & Leishman, 2013).
Research about spatiotemporal ecological representations of species has increased considerably in recent years with the advancement of geoprocessing and species distribution modeling tools by ecologists and conservation managers, and thus the need to provide efficient assessments of these predictive models (Teles, 1996; Allouche, Tsoar, & Kadmon, 2006). Species Distribution Models (SDMs) allow spatial extrapolation of known occurrence records at different scales and generate potential distribution maps based on the effects of climate change on species distribution (Teles, 1996; Costa, Carnaval, & Toledo, 2012; Oliveira & Cassemiro, 2013).
Although the assessment of the effects of climate change on Brazilian biodiversity is increasing in all biomes, especially those predominantly forested and with greater species richness and endemism (Amazon and Atlantic Forest) (Aleixo, Albernaz, Grelle, Vale, & Range, 2010), there are few attempts to predict the impacts on non-forest areas (Siqueira & Peterson, 2003; Terribile et al., 2012). High levels of environmental devastation have made Cerrado to be included in the list of biodiversity hotspots (Myers, Mittermeier, Mittermeier, Fonseca, & Kent, 2000; CI, 2019), and yet minimal (scientific and political-social) attention has been given to the marginal and disjointed position of the savannas of the North and Northeast, called the modern Brazilian agricultural frontier. They refer, in large part, to “MATOPIBA”, a portion of the North and Northeast savannas with more than 73 million hectares (8.5% of the Brazilian territory), recognized as the portion between the states of Maranhão, Tocantins, Piauí and Bahia (Heck & Menezes, 2016) that accounts for much of Brazil’s grain and fiber production (https://www.embrapa.br/tema-matopiba).
Despite its importance, there is a growing concern with maintaining biodiversity and understanding the ecological relationships among local species, intensified by projections of climate scenarios. In order to strengthen conservation strategies in this ecological transition region in central-north Brazil (from the Amazon to the Brazilian Sertão), this research applied spatial analysis procedures and modeling tools to predict the potential distribution of “marginal” species (on the edge of the Cerrado biome) in this subset of priority ecotonal biodiversity for conservation, which we are calling hereafter a sub-hotspot.
Based on the physical-environment (thematic maps) and biological (species occurrence) variables of the current times, algorithms were applied in order to model the fundamental niche and the potential area of occurrence of the species. The following questions were investigated in this study: based on the potential current occurrence range of the target species, do the impacts of future climate change on their distribution predict retraction or expansion of the forecasted occurrence of the central-north peripheral Cerrado? Do predictions of future occurrence among species of wide geographical distribution differ from those of relatively more restricted to the northern portion of the Biome? Are environmentally stable areas of future predicted scenarios located inside Conservation Units (CUs) at present? In this context, this study aimed to estimate the impact of climate change on the future extent of occurrence of peripheral cerrados of central-north Brazil.