Biology Reference
In-Depth Information
''in sufficiently complex systems, selection cannot avoid the order exhibited
by most members of the ensemble. Therefore, such order is present
not because of selection but despite it''; and ''many conceivable useful
phenotypes do not exist.'' Phenotypic evolution in one species corresponds
to a cloud of points (representing individuals) moving on a trajectory across
phenotypic space. Assuming the null hypothesis that there are no
constraints, a species can be thought as performing random-branching
walks in a multidimensional phenotypic space, most of which is empty.
Walks can be represented as occurring in rugged fitness landscapes. ''In a
fixed but rugged fitness landscape, radiation and ultimate stasis are utterly
generic. We require no special mechanism to account for such
phenomena'' (such as initially empty niche space which is progressively
filled). There is no need to assume filling of niche space or competitive
exclusion to slow radiation (Kauffman,
1993
, p. 77), because there are an
ever decreasing number of directions close to adaptive peaks. Walks always
stop at local optima below the global optimum.
In short, the existence of vacant niches is expected and widespread, and
no special mechanisms are necessary to explain their existence.
We conclude not only that many (and perhaps all) niches are under-
utilized by species, i.e., many vacant niches for further colonization exist,
but also that nonsaturation is strong evidence for nonequilibrium in
many communities.
