Eco-Evolutionary Assembly of Hyperdiverse Biotas


How do species-rich communities and regional biotas assemble?

Prescribed fire in a longleaf pine savanna (Camp Whispering Pines, Louisiana)

Species-rich groundcover plant community (Splinter Hill Bog, Alabama)

Dispersal, ecological drift, and niche selection in longleaf pine ecosystems 

Species-rich communities and regional biotas have inspired a rich body of theory to explain community assembly and the maintenance of biodiversity. In these communities, extreme numbers of species often occur together at small scales. Classic explanations for high local biodiversity emphasize the importance of deterministic abiotic and biotic processes that promote stable coexistence of species via niche selection. Yet species composition often varies substantially among communities with similar environmental conditions, suggesting important roles for dispersal limitation or neutral species interactions and other stochastic processes that cause ecological drift. Moreover, processes at larger spatiotemporal scales such as speciation and the dynamics of regional species pools may also determine how species-rich communities assemble. Species-rich communities therefore provide an ideal setting for exploring the ways in which multiple processes at different scales interface to determine the assembly, diversity, and dynamics of local communities and regional biotas.

We are experimentally testing the relative importance of dispersal limitation, ecological drift, and niche selection (e.g., environmental filtering from drought and fire; interspecific competition from dominant species; species sorting across soil-resource gradients) as drivers of biodiversity and community assembly in the hyperdiverse longleaf pine (Pinus palustris) ecosystem. Historically, this ecosystem spanned the North American Coastal Plain, a global biodiversity hotspot that supports >1,600 endemic plant species (Noss et al. 2015). At local scales, the longleaf pine ecosystem supports the highest plant species richness in North America (40-50 species/m²) and is among the world’s most threatened ecosystems (>98% habitat loss), providing abundant opportunities to contribute towards biodiversity conservation, ecological restoration, and land management.

Key Findings & Research Highlights

  • We reviewed ecological theories of community assembly and biodiversity in species-rich plant communities, empirical evidence for mechanisms that create and maintain high plant species diversity at local and regional scales in longleaf pine ecosystems, and identified key research gaps to help inform ecological restoration (Kirkman & Myers 2017, Ecological Restoration and Management of Longleaf Pine Forests).
  • Dispersal increases plant species richness in the presence of both environmental filters (drought & small-scale heterogeneity in fire disturbance) and biotic interactions with dominant plant species (bunchgrasses), suggesting that dispersal limitation generally overrides the importance of local niche selection in the assembly of species-rich communities (Myers & Harms 2009, Ecology; Myers & Harms 2011, Ecology; Harms et al. 2017, Ecosphere).
  • Environmental filters (drought & small-scale heterogeneity in fire disturbance) alter effects of dispersal on plant recruitment and species richness, suggesting ecological conditions that mediate the relative importance of dispersal and niche selection within species-rich communities through space and time (Myers & Harms 2011, Ecology).
  • In contrast to the prevailing paradigm for many plant communities, we found that competition from common species (bunchgrasses) has weak influences on species richness, relative abundances of immigrating species, and beta-diversity, suggesting a limited role for interspecific competition as a mechanism of local niche selection in species-rich communities (Myers & Harms 2009, Ecology; Catano et al. 2017, Ecology Letters).
  • Small-scale heterogeneity in fire disturbance, and differences in how common species (bunchgrasses) tolerate fire may together promote shared local dominance among species within common guilds in species-rich communities (Gagnon et al. 2012, PLoS ONE).
  • Our fire-ecology research implicates soil heating as a key driver of community assembly and suggests that extreme flammability of above-ground organs in many plants from fire-prone ecosystems may be an adaptive mechanism to help protect below-ground regenerative organs and seeds during fires (Gagnon et al. 2010, Ecology; Gagnon et al. 2015, Journal of Ecology).

Field Sites

Our field sites include wet (e.g., savanna), mesic (e.g., flatwood), and dry (e.g., sandhill) longleaf pine communities on private and public lands in Florida (e.g., Eglin Air Force Base) and Louisiana (e.g., Camp Whispering Pines Girl Scout Camp; Abita Creek Flatwoods & Lake Ramsay Natural Conservancy Preserves).

Quadrat (1 x 1 m) containing ~40 plant species in a mesic longleaf pine savanna,
Camp Whispering Pines, Louisiana

Sundew (Drosera sp. [Droseraceae])
in a wet longleaf pine savanna,
Apalachicola National Forest, Florida

Longleaf “Diversity, Dominance & Disturbance (3D)” Team, Eglin Air Force Base, Florida (Aug. 2013)

 

This gallery includes images from:

  • Abita Creek Flatwoods Nature Conservancy Preserve, Louisiana
  • Apalachicola National Forest, Florida
  • Blackwater River State Park, Florida
  • Camp Whispering Pines, Louisiana
  • DeSoto National Forest, Mississippi
  • Eglin Air Force Base, Florida
  • Ocala National Forest, Florida
  • Ordway-Swisher Biological Station, Florida
  • Splinter Hill Bog Nature Conservancy Preserve, Alabama
  • St. Joseph Bay State Buffer Preserve, Florida

Broader Impacts

In addition to our basic research in community assembly and fire ecology, abundant opportunities have emerged to also contribute towards conservation in longleaf ecosystems through educational and management-based outreach. Our outreach activities have included nature programs for Girl Scouts and the general public at Camp Whispering Pines (Louisiana) and a longleaf groundcover workshop at the Longleaf Alliance 10th Biennial Conference in Mobile, Alabama (e.g., our workshop report and recommendations we submitted to the 2014 Longleaf Partnership Council).

Acknowledgements & Collaborators

Principal collaborators include Kyle Harms (Louisiana State University) and Paul Gagnon (Murray State University). We thank the Eglin Air Force Base (especially Jackson Guard), the Girl Scouts of America and Camp Whispering Pines Girl Scout Camp, the Nature Conservancy and Abita Creek Flatwoods and Lake Ramsay Nature Conservancy Preserves, and the National Science Foundation (DEB 1144084) for supporting our research.