Community assembly rules are a set of controversial rules first proposed by Jared Diamond.[1] The rules were developed after more than a decade of research into the avian assemblages on islands near New Guinea and assert that competition is responsible for determining the patterns of assemblage composition. Diamond's paper sparked nearly two decades worth of controversy in the literature spanning from the late seventies through the late nineties and is considered a turning point in community ecology. The disagreement continues to this day.
The first rule is "forbidden species combinations". Example: the black honeyeater excludes the black sunbird. The black honeyeater, Myzomela pammelaena, lives on 23 of the 41 surveyed islands in the Bismarck Archipelago, but not on any of the 14 islands inhabited by the black sunbird, Nectarinia sericea. Both birds are about the same size and use curved bills to sip nectar, and Diamond noted that competition affects their distribution [2]. Diamonds hypothesis was that competition and not random immigration was the main force structuring the species composition of islands.
Testing the assembly rules is a complex process that often uses computer simulations to compare characteristics of random assemblages of species to experimental data. The rules are generally regarded as hypotheses that need to be tested on an individual bases, not as accepted conclusions.
Case[3] tested the assembly rule that species occurring together on islands should have less niche overlap than random assemblages because they have undergone specialization. His study measured niche overlap of lizards on 37 islands near Baja California and compared niche overlap to the median niche overlap of computer generated random species assemblages. He found that 30 of the 37 islands had lower niche overlap than the random assemblages and that some of the competition is due to interspecific competition.
As a reaction to the assembly rules controversy ecologist Stephen Hubbell (1997) proposed that the abundance and diversity of species in a community is determined mainly by random dispersal, speciation, and extinction. This came to be known as the unified neutral theory of biodiversity.
  | Ecology and Evolution of Communities - Harvard University Press: Ecology and Evolution of Communities by Martin Cody |
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