My background in macroecology, plant geography and macroevolution gives me a unique perspective for addressing questions about interactions of the environment with plant diversity and function, and their global change implications. During the next five years, I will build on this background to develop a research program focused on the mechanisms linking functional traits and biodiversity across climatic and edaphic gradients and across multiple spatial and temporal scales. Below I outline two collaborative and ongoing projects that will be the basis for the beginning of this research program.
1) Macroecology of land plant biodiversity. Land plant biodiversity is strongly correlated with climate. More importantly, plant diversity is organized climatically into biomes that are to some extent evolutionarily distinct, with physiognomies characterized by the functional traits of the dominant species. Functional differences among biomes are critically important to modeling the global carbon cycle and the functioning of the Earth system. Therefore, in order to anticipate ecosystem responses to climate change, we must understand how the functional diversity of land plants has evolved in response to past changes in climate. The association between vegetation physiognomy and climate dates to the pioneering insights of von Humboldt, but scientists have only begun to develop a predictive science of biodiversity to explain the diversity-climate relationship based on the underlying ecological and evolutionary processes of diversification, dispersal, adaptation and coexistence. A few studies have considered the assembly of continental-scale biomes in this light. Nonetheless, progress has been limited in part by informatics challenges associated with standardizing and integrating large disparate datasets to model the geographic distributions, functional traits and phylogenetic relationships of species. To address these issues, a research group led by Brian Enquist (University of Arizona) has assembled the largest and most comprehensive botanical distribution database, detailing the geographical ranges, niche characteristics and evolutionary relationships of more than 100,000 New World plant species. In collaboration with B. Enquist and Drew Kerkhoff (Kenyon College), I will then use novel informatics approaches to reconstruct the evolutionary history of plant ecology and biogeography, in order to discover whether the colonization of novel environments is limited by niche evolution, and whether less physiologically favorable environments actually impose hard ecological limits on the number of plant species they can support.
2) Niche evolution of South American trees and its consequences. This project aims to make a fundamental advance in our knowledge of the processes that have created patterns of diversity in the tropics by gaining a better understanding of the evolutionary timing and rate of biome switching in plant lineages. More specifically, we aim to provide the first large-scale assessment of the relative importance of climatic and edaphic factors in driving diversification in tropical trees. This knowledge is fundamentally important both as a foundation for future studies of tropical plant diversification – for example, frequent switching between biomes suggests adaptation to new environments is an important part of the speciation process – and also for designing conservation strategies that incorporate an evolutionary perspective. To achieve these goals, we built a collaborative effort that is led by Toby Pennington (University of Exeter), Kyle Dexter (University of Edinburgh), Tim Baker (University of Leeds), Ary Oliveira-Filho (Universidade Federal de Minas Gerais, Brazil) and myself, and have already fulfilled the first objective: integrate plot and community survey data from seasonally dry tropical forest (SDTF), savanna and rain forest in South America, and thus create a dataset of floristic composition unparalleled in its ecological breadth and detail, spanning ~2500 sites. We also synthesized taxonomic determinations for the genera of angiosperms (flowering plants) and species of Leguminosae (the legume family) found in the plots, obtained climatic (temperature, precipitation) information for all sites, and collected or compiled standardized data on soil fertility for 150 plots across all three biomes. Over the next two years, our objectives are: 1) Quantify the climatic and edaphic niches of (i) all adequately sampled genera; and (ii) all adequately sampled species of Leguminosae. 2) Reconstruct phylogenetic relationships of (i) all genera found in the plots; and (ii) of species of Leguminosae found at >10 plots, using existing and de novo sequence data. 3) Test a series of specific hypotheses about the relative frequency of different biome shifts related to the current ecology and geologic history.