Eiserhardt, Wolf L.5; Svenning, J.-C.5; Baker, William J.3; Couvreur, Thomas L.P.4; Kissling, W. Daniel5; Balslev, Henrik5
1 Ecoinformatics & Biodiversity, Faculty of Science, Aarhus University, Aarhus University2 Department of Bioscience - Ecoinformatics and Biodiversity, Department of Bioscience, Science and Technology, Aarhus University3 Royal Botanic Gardens, Kew4 The New York Botanical Garden5 Department of Bioscience - Ecoinformatics and Biodiversity, Department of Bioscience, Science and Technology, Aarhus University
Palms lend themselves to exploring approaches at the intersection of ecology and phylogenetics. They are taxonomically diverse, often key functional components of ecosystems, and form complex assemblages of different co-existing life-forms. Recent advances in palm phylogenetics, including a dated genus-level supertree covering all genera, allow new insights into the ecological and evolutionary processes that underlie this diversity. We used phylogenetic information and species distribution data to study the mechanisms behind diversity, composition, and structure of palm assemblages on different spatial scales. Among others, we ask the following questions: To what extent can niche conservatism explain large-scale distribution patterns? Which assembly mechanisms are responsible for palm community composition on different spatial scales? What is the role of phylogenetic history for spatial patterns in functional assemblage structure? Our analyses are based on distribution data ranging from local to global scales: (a) a dataset including >340,000 palm individuals in 430 transects in the Western Amazon, (b) a set of gridded distribution maps for all New World palm species (n=550) and (c) global country-level presence/absence data of all (>2400) palm species. On a global scale, biogeographic regions show pronounced differences in the degree of palm phylogenetic clustering. The Neotropics and a number of islands, notably Madagascar, but also e.g. New Caledonia, Hawaii, and Cuba, stand out with remarkably high clustering. On a continental scale in the New World, we inferred from phylogenetic turnover that palms diversified mainly within seven biogeographic regions. This pattern of in situ diversification is strongly driven by a combination of phylogenetic niche conservatism, environmental filtering and dispersal limitation. Niche conservatism with respect to temperature seasonality and extremes emerges as an important determinant of palm species and clade distributions and thus there is concern that palms might be considerably vulnerable to climate change. On a regional to local scale in the Western Amazon, preliminary results show phylogenetic overdispersion of palm communities (i.e., co-occurring species are less closely related than expected at random). This implies that community composition is influenced by inter- specific competition (conserved alpha-niche) and/or adaptive speciation in response to spatially structured environmental factors (convergent beta-niche). Our findings indicate that the impact of environmental factors on the distribution of palm diversity can be understood much better in the light of phylogenetic history, challenging the traditional view that contemporary environment is the predominant driver of biodiversity patterns. Understanding how the distribution of species and thus biodiversity is influenced by the environment, and on which timescales these interactions take place, is urgent in times of anthropogenic climate change. It appears that phylogenetics can bridge a long-standing gap between ecology and evolution, and allow a holistic view on the causes of spatial biodiversity patterns.