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Niches versus Neutrality

Niches versus Neutrality. Pennisi (2005, Science 309:93) 25 Most Important Questions in Science Include What explains species coexistence in diverse communities ?. Niche Differences. Self-Regulation Stronger than Interspecific Competition Stabilizes, Coexistence Ecologists

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Niches versus Neutrality

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  1. Niches versus Neutrality Pennisi (2005, Science 309:93) 25 Most Important Questions in Science Include What explains species coexistence in diverse communities?

  2. Niche Differences Self-Regulation Stronger than Interspecific Competition Stabilizes, Coexistence Ecologists Patterns in Communities of Similar Species due to Niche Differences, Implying That Self-Regulation Stronger than Interspecies Interaction, Equilibrium Perspective

  3. Neutral Models Past Decade Some Larger-Scale PatternsExplained Without Invoking Niche Differences Among Species Only Similar Species/Same Trophic Level Equivalent Species: Same Birth/Death Rates Respond to Environment Same Way: Species Do Not Differ in Ways Distinguishing Their Dynamics

  4. Patterns Rank Abundance Curves Species-Area Relationship Diversity-Distance Relationship Range Size-Abundance Plots Community Ecology and Macroecology Fit by Neutral Models with Tuned Immigration Rates Controversy, Careful Interpretation/Comparison

  5. Niche Differentiation Strong Evidence, Many Communities, Gradients Study-Communities Biased by Anticipation? Niche Model IndividualA Amid Sp A Lower Growth Rate Than IndividualA Amid Sp B – Sp A May Invade Sp B Neutral Model Same Rate, Species Equivalent Preemptive Competition: Same Niche

  6. Neutral Model Competition Possible: Preemption of Space But No Species Differentiation Neutral Model Equivalence: Species Identical Demographic Rates  Coexistence is Co-occurrence Densities Drift Randomly (Neutrally)

  7. Neutral Model Neutrality and Niche Theory Not Mutually Exclusive cf. Selection vs Neutral Evolution Null Hypothesis, Neutral Not Random Parsimony?

  8. G. Bell (2001) Science 293:2413. Proponent of Neutral Model “… patterns can be shown to arise … from neutral community models in which all individuals have identical properties, as the consequence of local dispersal alone.”

  9. Bell (2001) Science 293:2413. Neutral Community Model (NCM) Each Indvidual: Pr[birth] = b, Pr[death] = d K or fewer individuals in community, K fixed Pr[immigrant of species] = m; same for each species N total species in external pool Simulate until equilibrates statistically (not ecologically)

  10. Distribution of Abundance Ecologists Competitive Variation: Geometric Abundances Niche Preemption Large, Biotic Communities: Random, Multiplicative Interactions Produce Lognormal Densities

  11. Bell (2000) Am Nat 155:606 Simulated Neutral Community, Tuned Migration Probability Breeding Birds, British mainland Lognormal

  12. Variation In Range Size Ecologists Log-Series: Habitat availability, Specialist vs generalist requirements, Environmental tolerance, Dispersal ability “Niche breadth”

  13. Bell (2001) Science 293:2413 New World Birds Australian Passerines North American Birds Neutral Community Model with 1600 Spatial Sites

  14. Range-Abundance: Power Law Species with more individuals occupy larger geographical ranges. Ecologists Habitat generalization Cosmopolitan resource Etc.

  15. Bell(2001) Wildfowl Neutral Community Model Varying Block Size, Basis for Presence/Absence in Range Estimation

  16. Species-Area Relationship

  17. Conclude? Neutral model, with appropriate choice of birth, death, and migration rates – applied to all species – can produce macroecological patterns observed in nature. Intellectual/scientific precedence (parsimony) over ecological principles?

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