Drivers of floristic variation in biogeographic transitions: insights from the ecotone between the largest biogeographic domains of South America

Abstract

ABSTRACT 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.

Keywords

• biogeographical patterns
• ecological transitions
• ecotone
• floristic variation
• tb-RDA
• variance partitioning
• vegetation types