Neutral Theory: Ecological Drift & Speciation

Hubbell (2001) • zero-sum dynamics • species abundance distribution • θ = 2Jm·ν

Community Parameters

Neutral death-birth:
1 individual dies
→ replaced by offspring
of random neighbor
(prob 1−m) or
immigrant (prob m)

θ = 2·J·ν (biodiv. #)
Fisher log-series SAD:
E[nₖ] = θ·xᵏ/k
S = – species | H' = –
θ = – | Dominant: –%
Hubbell's Unified Neutral Theory (2001): all species ecologically equivalent. Diversity maintained by balance of speciation/immigration vs. drift. Predicts Fisher's log-series species abundance distribution — tested against tropical forest data from Barro Colorado Island.