The Emergence and Promise of Functional Biogeography Cyrille Viollea,B,1, Peter B
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SPECIAL FEATURE: INTRODUCTION The emergence and promise of functional biogeography Cyrille Viollea,b,1, Peter B. Reichc,d, Stephen W. Pacalae, Brian J. Enquistf,g,h, and Jens Kattgei,j aCentre d’Ecologie Fonctionelle et Evolutive, Unité Mixte de Recherche 5175, Centre National de la Recherche Scientifique, Université de Montpellier, Université Paul-Valéry Montpellier, École Pratique des Hautes Études, F-34293 Montpellier Cedex 5, France; bCentre de Synthèse et d’Analyse sur la Biodiversité/Fondation pour la Recherche sur la Biodiversité, Domaine du Petit Arbois, Avenue Louis Philibert, 13545 Aix-en- Provence, France; cDepartment of Forest Resources, University of Minnesota, St. Paul, MN 55108; dHawkesbury Institute for the Environment, University of Western Sydney, Penrith, NSW 2751, Australia; eDepartment of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544; fDepartment of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721; gThe Santa Fe Institute, Santa Fe, NM 87501; hThe iPlant Collaborative, Tucson, AZ 85721; iMax Planck Institute for Biogeochemistry, 07745 Jena, Germany; and jGerman Centre for Integrative Biodiversity Research Halle-Jena-Leipzig, 04103 Leipzig, Germany Understanding, modeling, and predicting the impact of global change on ecosystem functioning across biogeographical gradients can benefit from enhanced capacity to represent biota as a continuous distribution of traits. However, this is a challenge for the field of biogeography historically grounded on the species concept. Here we focus on the newly emergent field of functional biogeography: the study of the geographic distribution of trait diversity across organizational levels. We show how functional biogeography bridges species-based biogeography and earth science to provide ideas and tools to help explain gradients in multifaceted diversity (including species, functional, and phylogenetic diversities), predict ecosystem functioning and services worldwide, and infuse regional and global conservation programs with a functional basis. Although much recent progress has been made possible because of the rising of multiple data streams, new developments in ecoinformatics, and new methodological advances, future directions should provide a theoretical and comprehensive framework for the scaling of biotic interactions across trophic levels and its ecological implications. biodiversity | functional trait | predictive ecology Biogeography is the study of the distribution maps of priority areas for conservation and functional types (PFT), characterized by of species and ecosystems across space and projections of the effects of global change on mean ecophysiological characteristics, are time and of the underlying biotic and abiotic species diversity patterns for the next century used per biome in models dedicated to sim- factors, mechanisms, and processes (1). Bio- (6–9). Nonetheless, predictions of how eco- ulate and forecast the consequences of geography is central to synthesizing small- logical communities respond to past and pro- global changes on biogeochemical cycling and large-scale patterns of species’ responses jected future climates have increasingly been (24). However, in biodiversity–ecosystem to global environmental change and provid- challenged (10) due to the limitations of spe- functioning research (25–27), the taxonomic ing a window to assess the importance of cies-based approaches, including conceptual composition of an ecosystem is identified as earth and evolutionary history, as well as and technical difficulties in incorporating a key driver of ecosystem functioning. More changing biotic and abiotic factors that un- species interactions, dispersal limitations, recently, the functional component of biodi- derlie the current distribution of taxa. Histor- and species’ adaptations into predictive mod- versity, i.e., the diversity of forms and func- ically, biogeography has been rooted in the els (11–16). Indeed, if we treat species as tions, has been recognized as the missing link species concept. Biologists long ago built qualitative entities, then we need to under- between biodiversity patterns and biogeo- – global maps of species’ ranges and species stand each and every one. In contrast, trait- chemical cycles (28 30) and perhaps is a diversity patterns, which allowed scientists based biogeography can help model species core driver of ecosystem services (31, 32). to develop, test, and validate prominent eco- interactions, dispersal ability, and physiolog- Given these insights from ecosystem ecology, there is a growing consensus on the need logical theories at the root of biogeography ical tolerance more simply and generically — (2, 3). Biogeography, however, has largely de- (17). More precisely, if we array species along for a better representation of biodiversity in particular the composition of species, veloped separately from ecosystem ecology some continuous trait axes (18), then know- forms, and functions—in earth science and earth system biology, yet we argue that ing cross-species relationships (19), e.g., models (21, 23, 24), as stressed in this issue one of the great challenges of 21st century between plant physiological tolerance to by Reichstein et al. (33). biogeography is to provide theoretical base- drought and diameter of xylem vessel (20), In this Introduction, and in the related lines and tools for the understanding and can help forecast the change in species com- special feature, to bridge historical species- prediction of ecosystem responses to envi- position of ecological communities in re- based biogeography with earth systems ronmental changes in terms of species com- sponse to variation in abiotic conditions position and biogeochemical cycles (water, like water availability. carbon, nutrients, and energy). Contrary to species-based biogeography, Author contributions: C.V., P.B.R., S.W.P., B.J.E., and J.K. designed research, performed research, contributed analytic tools, and For the last several decades, new directions earth science models directly address changes wrote the paper. in biogeography have been aided by statistical in biogeochemical cycles at a global scale The authors declare no conflict of interest. and computational advances (4, 5), and new but using a simplistic representation of 1To whom correspondence should be addressed. Email: cyrille. species distribution models have provided biodiversity in most cases (21–24): few plant [email protected]. 13690–13696 | PNAS | September 23, 2014 | vol. 111 | no. 38 www.pnas.org/cgi/doi/10.1073/pnas.1415442111 Downloaded by guest on September 28, 2021 science, we argue that the time is ripe to or behavioral features measured on organ- variation within species across space (e.g., INTRODUCTION advance functional biogeography. We define isms that can ultimately be linked to their within the range of species) represents one SPECIAL FEATURE: functional biogeography as the analysis of performance (40). In trait-based ecology, it primary aspect of functional biogeography the patterns, causes, and consequences of has been shown that it is possible to aggre- (63, 64). Future efforts to quantify both in- the geographic distribution of the diver- gate functional traits measured on organisms traspecific phenotypic and genetic varia- sity of form and function—namely, trait to explain the functioning of populations, tion within species’ ranges should bring diversity. Indeed treating the biota as a con- communities, ecosystems, and beyond. For interesting insights into the eco-evolutionary tinuous distribution of traits appears pivotal instance, at the community level, the use of drivers of species’ distributions and help if one is expected to model the biosphere community-weighed means (CWM, i.e., the bridge functional ecology, spatial ecology, when there are literally millions of separate average trait value of a community account- genetics, and evolutionary biology (65) species. Describing and explaining the ing for effects of species abundance within (Fig. 1). The question of accounting for global distribution of forms and functions communities) (40, 41) is a promising tool to intraspecific variation in cross-species trait- is a long-standing goal for ecologists (34– accurately predict ecosystem functions such based studies has been extensively discussed 36). Such attempts have been synthetized as plant primary productivity (41, 42). As for the last 5 years (52, 66, 67). The impor- under a variety of terms including macro- a whole, functional traits can be imple- tance of accounting for intraspecific vari- physiology (19, 37–39). The emergence of mented into more or less complex inte- ation at macroecological scales, when functional biogeography pursues this goal grative functions (e.g., CWM is a simple interspecific variations are expected to be but also aims at linking biogeographical integrative function) to scale up from organs large, is still debated (21, 67–69). patterns of trait diversity to biogeographi- to higher organizational levels including A functional trait approach has now been cal patterns of species diversity, ecosystem ecosystems and biomes (40, 43, 44). Trait- rapidly and extensively developed in plant functioning, and services because of the in- based approaches have also been extensively ecology, aided by the development of stan- tegration of concepts and methodologies used to describe the diversity of forms and dardized protocols and methodologies (70, from multiple fields (Fig. 1). Advancing func-