Community assembly rules are a set of controversial rules in
ecology
Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...
, first proposed by
Jared Diamond
Jared Mason Diamond (born September 10, 1937) is an American scientist, historian, and author. In 1985 he received a MacArthur Genius Grant, and he has written hundreds of scientific and popular articles and books. His best known is '' Guns, G ...
.
Rules
The rules were developed after more than a decade of research into the avian assemblages on islands near
New Guinea
New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...
. The rules assert that competition is responsible for determining the patterns of assemblage composition.
Rule 1: Forbidden species combinations
The first rule is "forbidden species combinations". Diamond's hypothesis was that competition, not random immigration, was the main force structuring the
species composition
Relative species abundance is a component of biodiversity and is a measure of how common or rare a species is relative to other species in a defined location or community.Hubbell, S. P. 2001. ''The unified neutral theory of biodiversity and biogeog ...
of islands.
So for example, the
Bismarck black myzomela (''Myzomela pammelaena'') excludes the
black sunbird (''Nectarinia sericea''). The Bismarck black myzomela 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. The two birds are about the same size, and both use their curved bills to sip nectar; Diamond argued that competition affects their distribution.
Rule 2: Reduced niche overlap
Ted Case 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
Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...
and compared niche overlap to the median niche overlap of computer generated random species assemblages. Case 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
Interspecific competition, in ecology, is a form of competition in which individuals of ''different'' species compete for the same resources in an ecosystem (e.g. food or living space). This can be contrasted with mutualism, a type of symbiosis. ...
.
Testing and alternative theories
Testing the assembly rules is a complex process that often uses computer simulations to compare experimental data with characteristics of random assemblages of species. The rules are generally regarded as hypotheses that need to be tested on an individual basis, not as accepted conclusions. This is the reason why Diamond's results sparked nearly two decades worth of controversy in the literature, from the late seventies through the late nineties and is considered a turning point in
community ecology
In ecology, a community is a group or association of populations of two or more different species occupying the same geographical area at the same time, also known as a biocoenosis, biotic community, biological community, ecological communit ...
.
led the arguments against these rules claiming that theory as the one developed by Diamond "has generated predictions that are either practically untestable, by virtue of unmeasurable parameters or unrealizable assumptions, or trivially true".
The controversy was developed in a number of scientific papers (see for instance
and ) and contributed to the development of null and
neutral models in community ecology, which are nowadays widely used to test the significance of ecological patterns.
References
Further reading
{{DEFAULTSORT:Assembly Rules
Ecological theories
Rules
Evolutionary biology