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“Soft” Approaches to Regional Species Pools for Plots

“Soft” Approaches to Regional Species Pools for Plots. Tom Wentworth, Jason Fridley, Joel Gramling, Todd Jobe Ecoinformatics Working Group November 25, 2002. What is a regional species pool?.

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“Soft” Approaches to Regional Species Pools for Plots

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  1. “Soft” Approaches to Regional Species Pools for Plots Tom Wentworth, Jason Fridley, Joel Gramling, Todd Jobe Ecoinformatics Working Group November 25, 2002

  2. What is a regional species pool? • Bob Ricklefs (TEON, 5e, 2001): “The species that occur within a region are referred to as its species pool. All the members of the regional species pool are potential members of each local community.”

  3. Local communities are subsets of the regional species pool. • More from Bob Ricklefs (TEON, 5e, 2001): “A central concept of ecology is that membership in local communities is restricted to the species that can coexist together in the same habitat. Thus, each local community is a subset of the regional species pool.”

  4. Species sorting: experimental study of 20 wetland species seeded into 120 wetland microcosms representing varied environments Work of Weiher and Keddy…

  5. Bob Ricklefs (TEON, 5e, 2001): “Interactions of species within local habitats make up only half of the diversity equation.”

  6. Regional vs. Local Effects

  7. So what? • The relationship between the regional species pool and local community is mediated by important processes fundamental to our understanding of how local communities are organized: • dispersal • habitat selection • predatory and competitive exclusion • chance extinction

  8. Interesting questions: (1) Is there proportional sampling vs. saturation?

  9. Interesting questions: (2) What is the extent of nestedness?

  10. We gain important insights from examination of species pools.

  11. Our Challenge: Building Species Pools • We don’t know the species pools contributing to our plots: • we could accept arbitrary definitions, but… • objective approaches are preferable: is there a bottom-up approach?

  12. “Hard” vs. “Soft” Approaches (sensu Fridley) • Hard: species are associated with one another through co-occurrence in plots: • species pools are built through “chains” of co-occurrence among species • Soft: species pools are constructed as plots/species are accumulated by “proximity”: • geographic (limited utility, but traditional) • environmental (attractive as we gather data) • compositional (most accessible)

  13. Soft Pools: Geographic Basis • Place plots in a geographic space (x, y, maybe z): • select a plot • accumulate species in the regional pool from nearest neighbor plots • add species until…when???

  14. Soft Pools: Geographic Basis • We don’t think this is necessarily the best idea: • no well-defined stopping point • accumulating species through geographic proximity builds pools with “strange bedfellows” (consider the longleaf savannah adjacent to a pocosin)… • but perhaps this is consistent with Ricklefs’ definition of regional species pools?

  15. Soft Pools: Environmental Basis • Place plots in an environmental space • select a plot • accumulate species in the regional pool from nearest neighbor plots • add species until you… • reach a plot that shares no species with starting plot • reach some arbitrarily determined distance

  16. Soft Pools: Environmental Basis • We like this idea: • support from work by Taylor, Aarssen et al. • builds pools using plots that are initially similar from an environmental perspective • NCVS data base is richly endowed with environmental data

  17. Soft Pools: Compositional Basis • Place plots in an compositional space • select a plot • accumulate species in the regional pool from nearest neighbor plots • add species until you… • reach a plot that shares no species with starting plot • reach some arbitrarily determined distance

  18. Soft Pools: Compositional Basis • We like this idea: • builds pools using plots that are initially similar from a compositional perspective • not restricted by limited availability of environmental data

  19. Soft Pools: Alternatives • Plot-based environmental and compositional spaces can also be populated with species: • why not build pools based on species’ centers and accumulate these in a nearest-neighbor approach? • a nice start, but ignores differential niche breadths of species…

  20. Soft Pools: Alternatives • Plot-based environmental and compositional spaces can also be populated with species: • why not build pools based on distributions of species overlapping a particular plot? environmental or compositional gradient

  21. Problems… • How many axes for environmental or compositional space? • as number of axes increases, species pool collapses to the species present in the plot • could limit analysis to n compositional or complex environmental axes (from PCA), but how many? • Edge effects limit detectability of species pools for marginal plots

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