Community Assembly from Local to Global Scales

What processes determine community assembly across large-scale diversity gradients?

One of the most prominent and ubiquitous patterns of life on earth is the systematic increase in species diversity from temperate to tropical latitudes. Yet the processes underlying this and other prominent biodiversity gradients have been difficult to distinguish because different processes operating at multiple scales may determine geographic variation in biodiversity. To untangle these processes, we are investigating the way in which deterministic and stochastic community assembly processes at local scales (e.g., dispersal limitation, ecological drift, niche selection resulting from abiotic conditions or biotic interactions within and among species) interact with processes at larger spatiotemporal scales (e.g., speciation and its influence on the composition of regional species pools) to create variation in community composition (beta-diversity), functional-trait diversity, and species diversity within and across temperate and tropical regions.

Key Findings & Research Highlights

  • The latitudinal-gradient in tree-species diversity reflects not only stronger local biotic interactions (conspecific negative density dependence) at tropical versus temperate latitudes, but also a latitudinal shift in the strength of biotic interactions among common and rare species, suggesting that global patterns of biodiversity cannot be understood without considering the interplay of local biotic interactions and regional processes across temperate and tropical latitudes (LaManna et al. 2017, Science).
  • Across a 4,000-m elevational gradient in the Bolivian Andes, we found that elevational gradients in tropical forest beta-diversity reflect scale-dependent changes in the importance of local community assembly processes and regional species pools, with local assembly processes becoming more important at larger spatial scales, resulting in a mid-elevational peak in beta-diversity  (Tello et al. 2015, PLoS ONE).
  • Dissimilar processes of community assembly explain similar non-random patterns of beta-diversity across environmental and spatial gradients in temperate and tropical forests, suggesting that biogeographic differences in regional species pools alone cannot account for large-scale gradients in beta-diversity (Myers et al. 2013, Ecology Letters).
  • Regional sampling effects caused simply by changes in the sizes of species pools (gamma-diversity) explain latitudinal and elevational gradients of forest beta-diversity, suggesting that regional processes, rather than differences in local community assembly processes in temperate versus tropical ecosystems, explain global-scale patterns of beta-diversity (Kraft et al. 2011, Science).
  • We developed a conceptual framework for disentangling the relative importance of deterministic versus stochastic community assembly in generating beta-diversity along ecological gradients (e.g., biotic interactions, disturbance, productivity) and among biogeographic regions that differ in the sizes of regional species pools (Chase & Myers 2011, Philosophical Transactions of the Royal Society B).

Our Field Sites

Our field sites include: a long-term, 25-ha temperate-forest dynamics plot at Washington University’s Tyson Research Center (see the Tyson Research Center Plot page), which is part of the Smithsonian Center for Tropical Forest Science-Forest Global Earth Observatory (CTFS-ForestGEO), the largest, systematically studied network of forest-ecology plots in the world (Anderson-Teixeira et al. 2015); a large-scale network of 0.1-ha temperate forest plots across the Missouri Ozarks (Myers et al. 2013; Myers et al. 2015); and the Madidi Project, a large-scale network of tropical forest plots distributed across a 4,000-m elevational gradient in the Bolivian Andes (Tello et al. 2015).

        Smithsonian CTFS-ForestGEO Network of 63 Forest-Dynamics Plots in 24 countries

La Tintaya Plot Expedition Team,
Madidi National Park, Bolivia (Sep. 2012)

Photo Galleries & Videos

The Story and Science of a Forest Global Earth Observatory
Global Forest Network Cracks the Case of Tropical Biodiversity

Acknowledgements & Collaborators

Our principal collaborators have included: Jon Chase (German Centre for Integrative Biodiversity Research), Iván Jiménez (Missouri Botanical Garden), Peter Jørgensen (Missouri Botanical Garden), Sebastián Tello (Missouri Botanical Garden), Alfredo Fuentes (Herbario Nacional de Bolivia), Leslie Cayola (Herbario Nacional de Bolivia), members of the Madidi Project, and more than 100 collaborators from CTFS-ForestGEO. We thank Missouri State Parks, Saint Louis University’s Reis Biological Station, the Madidi Project and participating institutions (especially the Missouri Botanical Garden & the Herbario Nacional de Bolivia), Tyson Research Center, the International Center for Energy, Environment and Sustainability (InCEES) at Washington University in St. Louis, CTFS-ForestGEO, the CTFS-ForestGEO Grants Program, and the National Science Foundation (DEB 1256788 & DEB 1557094) for supporting our research.