Ecological transitions usually represent vulnerable ecosystems and high biodiversity. Investigating their drivers is important from both biogeographic and conservationist perspectives. One of these transitions is situated between the two largest biogeographic domains of South America-the Amazon and the Cerrado. We evaluated variation in tree floristic composition throughout this transition and assessed which factors explain this variation. We used 17,240 records of occurrences of 2,530 tree species from the NeotropTree database. We investigated variation in floristic composition using UPGMA cluster analysis with bootstrap resampling and NMDS ordination, and modeled the distribution of species in relation to environmental and spatial predictors by means of transformation-based Redundancy Canonical Analysis (tb-RDA) and variance partitioning. We found four general floristic groups: 1) flooded forests; 2) white sand dwarf-forests; 3) savannic and dwarf forests; and 4) non-flooded forest types. Floristic variation along the transition was influenced by the environment, especially variables related to fire and soil moisture, and by space, especially variables acting on broader scales. Correspondence between the environmental heterogeneity found throughout the transition and our results demonstrates once again the importance of conserving biogeographical transition zones in general, and the most comprehensive of South America in particular.

Given the substantial lacunas in the understanding of the occurrence and distribution of bat species in the eastern portion of the Brazilian state of Mato Grosso (Araguaia basin), this study presents an inventory of the species known to occur in the region, highlighting the areas sampled adequately and the species known to occur in conservation units. Georeferenced records of the occurrence of bat species in the region were obtained from published studies, scientific collections, through either the SpeciesLink network or directly from the curator, as well as the capture of specimens by our research group between 2008 and 2013. A 0.56 x 0.56 (latitude/longitude) grid was added to the map of the region for the quantification of the bat species richness of each grid cell. A total of 63 chiropteran species were recorded for the study area. Only 10 of the 30 grid cells had records of bats, and just three contained more than 20 species, and were considered to be sampled adequately on a minimal level. Bat species have been recorded in three conservation units, two state and one municipal. The number of species recorded represents 82.7% of the total of chiropterans known to occur in Mato Grosso, although 12 species were recorded in the state for the first time, reinforcing the paucity of data available on the distribution of bats in the region. The high bat species richness recorded in the present study reinforces the importance of eastern Mato Grosso, a transition zone between the Amazon forest and the Cerrado savanna of central Brazil, for the conservation of Neotropical chiropterans. Keywords: Cerrado savanna, geographic distribution, conservation units, chiropterans.OLIVEIRA, S.L., SOUZA, L.A.S., SILVA, H.K., FARIA, K.C. Configuração espacial da ocorrência de espécies de morcegos (Mammalia: Chiroptera) no leste de Mato Grosso, Brasil.

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