Environmental correlates of floristic regions and plant turnover in the Atlantic Forest hotspot

Abstract

Aim Using a comprehensive floristic database (2616 species, 36,004 occurrence records from 128 unique localities), we model species turnover along the central region of the Atlantic Forest hotspot to (1) test whether local rivers, particularly the Rio Doce, are associated with marked biogeographical breaks, and (2) investigate how regional compositional changes correlate with geo-climatic variables.Location The central region of the Atlantic Forest in eastern Brazil (12°-22°S latitude). MethodsWe combine occurrence and geo-climatic data in a generalized dissimilarity model, obtaining a continuous prediction of species turnover across space and identifying 12 significant geo-climatic predictors of community composition. We use a two-step cluster analysis to classify the turnover map into major floristic regions based on the natural subgroups observed. We further divide each major floristic region into smaller sub-regions based on natural subgroups statistically identified by the two-step cluster analyses.Results High levels of turnover in species composition occurred around latitudes 18°-19°S, c. 50-100 km north of the Rio Doce, and concurred with shifts in availability of both humidity and energy. We identified three major floristic regions in the central region of the Atlantic Forest, which we called Bahia Interior Forests, Bahia Coastal Forests, and the Kren ak-Waitak a Forestseach of them divided into two to four subregions.Main conclusions Our results suggest that local climatic conditions, not riverine barriers, drive biogeographical shifts in this region -a finding that supports studies of current and historical determinants of the composition of the Atlantic Forest biota. Floristic composition at higher elevations (> 600 m) is clearly distinct from those in lower elevations, likely as a result of physiological constraints imposed by cooler climates in the former. Floristic regions here identified from observed communities substantially improve the maps currently employed for conservation planning in a shrinking hotspot.

Woody plant subregions of the Amazon forest

“…In contrast to that has been found for a variety of tropical vegetation types and floristic assemblages (e.g. Cantidio & Souza, 2019;Castro-Insua et al, 2018;Linder et al, 2012;Marques et al, 2020;Saiter et al, 2016;Tuomisto et al, 2019), we found rather smooth borders between subregions. This is attributable to the absence of extensive mountain ranges or steep climatic gradients in most of the Amazon extension, as well as to the historical stability of the tropical forest biome in the basin (Costa et al, 2017), which may have allowed for extensive species dispersal.…”

“…Our results supported the recently raised point that vegetation maps based on physiognomic variation should not be used as proxies to plant diversity subregions, due to the marked mismatch between vegetation types and biodiversity subregions (Cantidio & Souza, 2019;Saiter et al, 2016;Silva & Souza, 2018a). For example, broadleaved evergreen pluvial forests cover most of the Amazon forest domain ( Figure S1), and yet we found different compositional subregions within this single physiognomy.…”

“…We also investigated the relationships of the identified subregions with environmental, historical and human correlates. Our results contribute to the global effort of mapping terrestrial subregions (Cantidio & Souza, 2019;Dinerstein et al, 2017;Moura et al, 2016;Olson et al, 2001;Saiter et al, 2016;Silva & Souza, 2018a) and for conservation planning in the Amazon domain.…”

“…Despite its global importance, and in spite of recent advances in the understanding of the distribution of its tree species and phylogenetic relatedness (Emilio et al, 2010;Oliveira & Nelson, 2001;Slik et al, 2018;ter Steege et al, 2000ter Steege et al, , 2013, a regionalization of the Amazon tree flora is still lacking. Clear and data-driven delimitation of subregions is a growing scientific enterprise (Cantidio & Souza, 2019;Moura, Argôlo, & Costa, 2016;Saiter et al, 2016;Silva & Souza, 2018a;Smith et al, 2018), with consequences for macroecological and biogeographical studies (Fine, 2015), to the practical identification of metacommunities (Leibold et al, 2004;Smith et al, 2018), to the understanding of animal distribution and evolution (Rueda, Rodríguez, & Hawkins, 2010), besides being a requisite for conservation planning and management (Dinerstein et al, 2017;Olson et al, 2001). Here we refer to subregions as land units containing distinct natural species assemblages delimited by their contemporary distribution (Olson et al, 2001).…”

Disentangling drivers of small mammal diversity in a highly fragmented forest system

“…However, when decoupling of FD into separate functional components, each showed varying relationships between landscape associations and different ecological characteristics for different assemblages (Cisneros et al, ). In the AF, precipitation and temperature variables have been shown to play important roles in structuring of invertebrate (Brown & Freitas, ), mammal (de la Sancha et al, ; Stevens, ), fish (Vilella, Becker, Hartz, & Barbieri, ), and plant (Leitman, Amorim, Sansevero, & Forzza, ; Zamborlini Saiter, Brown, Thomas, Oliveira‐Filho, & Carnaval, ) assemblages, communities, and metacommunities.…”