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Soft Approaches to Regional Species Pools for
Plots

• Tom Wentworth, Jason Fridley, Joel Gramling, Todd
  Jobe
• Ecoinformatics Working Group
• November 25, 2002

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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.

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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.

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Work of Weiher and Keddy

• Species sorting experimental study of 20 wetland
  species seeded into 120 wetland microcosms
  representing varied environments

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Bob Ricklefs (TEON, 5e, 2001) Interactions of
species within local habitats make up only half
of the diversity equation.
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Regional vs. Local Effects
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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

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Interesting questions (1) Is there proportional
sampling vs. saturation?
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Interesting questions (2) What is the extent of
nestedness?
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We gain important insights from examination of
species pools.
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Our Challenge Building Species Pools

• We dont know the species pools contributing to
  our plots
• we could accept arbitrary definitions, but
• objective approaches are preferable is there a
  bottom-up approach?

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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)

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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 untilwhen???

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Soft Pools Geographic Basis

• We dont 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?

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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

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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

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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

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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

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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

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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
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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