Niches versus Neutrality

Reviews of Neutral ModelsLevine & HilleRisLambers (2009) Nature

461:254.

Reviews

Hubbel (2001) The Unified Neutral Theory of Biodiversity and Biogeography. Princeton University Press.

Zero Sum Multinomial for Species AbundancesTuning Parameters, NCM versions of niche-preemption to lognormal species abundances

Reviews

Bell, Lechowitz &Waterway (2006) Ecology 87:1378.

Niches vs immigration

Predicted static patterns similarExperimental results strongly favor niche theory

Reviews

McGill, Maure & Weiser (2006) Ecology 87:1411.

Review testing neutral theory statistically

Available tests fail to support neutrality (only 1 exception)

Develop new test to distinguish zero-sum multinomial from lognormal species abundances

Neutral theory: Estimating parameters difficult/arbitrary

“… overwhelming evidence against neutral theory.”

Reviews

Purves & Turnbull (2010) J Animal Ecology 79:1215.

Stress implausibility of growth-rate equality assumed by NCM

Neutrality highly implausible

Similar views:

Gotelli & McGill (2006) Ecography 29:793

Niches and Neutrality

Currently, neutral models (approx. 10) lack both conceptual strength and empirical support.

Neutral models remind us that ecology, as a science, should link pattern (at a given scale) to process (often at a more restricted scale); description and statistical fit model prediction do not

validate model.

Niches and Maintenance of Diversity

Levine & HilleRisLambers (2009) Nature 461:254.

Levine & HilleRisLambers (2009)

Maintenance of ecological diversityFunctional, economic & aesthetic

Coexistence: Competitors’ niches differ;Stabilizes density-dependent dynamics, Per-capitum growth greater when rare

Challenge: Neutral theory: here, density-independent growth rates

Levine & HilleRisLambers (2009)Left: Self-Regulation Stronger than Interspecific Effect

Higher Growth Rate When Rare Produces Coexistence

Right: No Niche Difference, Implying Within-Species and Between-Species Effects Same

Levine & HilleRisLambers (2009)

Annuals on Serpentine SoilsSites: 10+ Species Co-OccurDiversity Niche Based?

Planted Experimental CommunitiesEach 10 SpeciesEqual Relative AbundancesGrowth-Rate Differences Reflect Inherent

Differences, Density-Variation Controlled

Levine & HilleRisLambers (2009)

Species Not Equivalent2 Orders of Magnitude in Geometric Mean

Neutral Model Assumptions:Self-Regulation Equal

to Between-Species Effect

Discrete-Time Dynamics:Competitive Exclusion

Species Diversity Seed pools control (any niche effects)Niches removed (equal effects)

Control (Niche differences)H’ 50% GreaterRare Species 35% Community

Niches RemovedRare Species 8% CommunityCommon Species More Common

Self-Regulated Growth: Seed Production

Signature of Coexistence via Self-RegulationNiche Differences