Defining Biologically Meaningful Biomes Through Floristic, Functional, and Phylogenetic Data

Domingos Cardoso,Gustavo Ramos,R. Toby Pennington,Graeme Oatley,Christopher Dudley,Peter W. Moonlight,Tiina E. Särkinen,Luciano Paganucci de Queiroz,Edeline Gagnon

doi:10.3389/fevo.2021.723558

Abstract

While we have largely improved our understanding on what biomes are and their utility in global change ecology, conservation planning, and evolutionary biology is clear, there is no consensus on how biomes should be delimited or mapped. Existing methods emphasize different aspects of biomes, with different strengths and limitations. We introduce a novel approach to biome delimitation and mapping, based upon combining individual regionalizations derived from floristic, functional, and phylogenetic data linked to environmentally trained species distribution models. We define “core Biomes” as areas where independent regionalizations agree and “transition zones” as those whose biome identity is not corroborated by all analyses. We apply this approach to delimiting the neglected Caatinga seasonally dry tropical forest biome in northeast Brazil. We delimit the “core Caatinga” as a smaller and more climatically limited area than previous definitions, and argue it represents a floristically, functionally, and phylogenetically coherent unit within the driest parts of northeast Brazil. “Caatinga transition zones” represent a large and biologically important area, highlighting that ecological and evolutionary processes work across environmental gradients and that biomes are not categorical variables. We discuss the differences among individual regionalizations in an ecological and evolutionary context and the potential limitations and utility of individual and combined biome delimitations. Our integrated ecological and evolutionary definition of the Caatinga and associated transition zones are argued to best describe and map biologically meaningful biomes.

Highlights

Biomes are a key concept in ecology and biogeography (Higgins et al, 2016; Mucina, 2019) and have been largely used in global change ecology (Prentice et al, 2007; Williams et al, 2007; Lehmann et al, 2014; Moncrieff et al, 2016), conservation planning (Hoekstra et al, 2005), and evolutionary biology (Donoghue and Edwards, 2014; Landis et al, 2021a)
While there is a consensus in ecology and biogeography that biomes should be defined based on physiognomy and functional aspects (Mucina, 2019; Pennington et al, 2018), an evolutionary dimension emphasizes the processes that have led to current biome distributions
We aim to demonstrate that a Caatinga SDTF biome, lying at the extremely dry end of the tropical seasonality and rainfall gradient of NE Brazil, greatly differs from nearby and interdigitating ecologically and evolutionarily distinct rainforest and savanna biomes and occupies a unique environmental space

Summary

Introduction

Biomes are a key concept in ecology and biogeography (Higgins et al, 2016; Mucina, 2019) and have been largely used in global change ecology (Prentice et al, 2007; Williams et al, 2007; Lehmann et al, 2014; Moncrieff et al, 2016), conservation planning (Hoekstra et al, 2005), and evolutionary biology (Donoghue and Edwards, 2014; Landis et al, 2021a). The concept has emerged partly in response to increasing evidence for the prevalence of phylogenetic niche conservatism (Crisp et al, 2009; Pennington et al, 2009; Oliveira-Filho et al, 2013a,b; Kerkhoff et al, 2014; Gagnon et al, 2019; Ringelberg et al, 2020; Segovia et al, 2020) This tendency of plant lineages to inherit their overall ancestral environmental niches is based upon evidence that many plant lineages have dispersed across large distances over evolutionary timescales yet occupy similar ecological conditions. The general lack of dispersal limitation and difficulty of accruing novel environmental adaptations had led to the popularity of the phrase that for plants, it is “easier to move than evolve” (Donoghue, 2008)

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