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presented by HNT is to justify invoking anything more complex than ecological drift
to defi ne community structure [5]. Its extravagant simplicity has had an explosive im-
pact on ecology (>1,100 citations, rising exponentially), because it appears to discount
100 years of traditional conventions on niche differentiation. If biodiversity encom-
passes the great richness of differently attributed species that constitutes the natural
world, how can ecological equivalence yield such predictive power about the numbers
of species [6]? If HNT is based on a ludicrous assumption [7], then our conceptual
understanding is thrown into disarray by its fi t to empirical patterns [8]. Here I ex-
plain this paradox in terms of the ecological equivalence realized by coexisting spe-
cies at demographic equilibrium. Analyses and simulations of co-existence equilibria
demonstrate the emergent property of ecological equivalence among species with a
rich diversity of attributes, leading to novel predictions for a quantifi able gradation in
species-area relationships between neutral and niche models.
A neutral model of empirical relationships eliminates “the entire set of forces com-
peting for a place in the explanation of the pattern” [9]. Accordingly, HNT assumes
that all species behave identically in a zero-sum game such that the total density of
individuals in a trophically similar community remains constant regardless of species
composition. The defi ning image of this ecological equivalence is a tropical forest
canopy, with remarkably constant total densities of trees regardless of large regional
variations in constituent species [1]. Interpretations of zero-sum equivalence routinely
omit to distinguish between the equal vital rates realized at the system carrying ca-
pacity approximated in this image (and most datasets), and the intrinsic vital rates
that defi ne the heritable character traits of each species. Models of HNT consistently
prescribe identical intrinsic rates and niche dimensions. Hubbell [1] anticipated the
disjuncture between realized and intrinsic rates by comparing ecological equivalence
to the fi tness invariance achieved at carrying capacity, allowing for different trade-off
combinations in life-history traits. The prevailing convention, however, remains that
ecological equivalence explicitly requires symmetric species with identical per capita
vital rates, thereby promulgating the notion that HNT is built on an unrealistic founda-
tion [3].
Theoretical studies have sought various ways to reconcile neutral patterns with
niche concepts. Intrinsically similar species can coexist under niche theory [7], and
niches add stabilizing mechanisms that are absent under the fi tness equivalence of
intrinsic neutrality [10]. Comparisons of niche to neutral simulations in a saturated
system of fi xed total abundance have shown that they can predict similar species-
abundance distributions (SADs) and species-area relationships [11], demonstrating
that neutral patterns need not imply neutral processes [12]. Even neutral processes of
intraspecifi c competition and dispersal limitation cannot be distinguished in principle
for species-abundance predictions [13-16]. Here I use an analysis and simulation of
Lotka-Volterra dynamics to model zero-sum ecological drift as an emergent property
of stochastic niche structures at dynamic equilibrium. I explain its appearance in the
steady-state distributions even of extremely dissimilar species in terms of the trivial
expectation that species must achieve ecological equivalence at their co-existence
equilibrium, which is defi ned by equal realized fi tness for all. Although the predictions
are standards of Lotka-Volterra analysis for a homogeneous environment, they drive
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