In this study, we put forward the hypothesis that the four species within the Ceratozamia norstogii complex, despite the low genetic variability between them, probably have originated from a genetically depauperate ancestor through an allopatric speciation
process, resulting from recent divergence due to genetic drift via founder effects.
Reproductive interference drives habitat differentiation between the two species when secondary contact occurs after allopatric speciation
The Refuge hypothesis refers to a particular mode of allopatric speciation
, but not to a particular time of differentiation.
In line with the popular theory of allopatric speciation
, previous thinking had been that the confinement of T.
Timing of this speciation event is therefore consistent with (but not proof of) allopatric speciation
The potential for allopatric speciation
at zoogeographic boundaries and the evolutionary role that zoogeographic barriers play in the generation of biological diversity is frequently discussed (Addicott 1966; Valentine and Jablonski 1983, 1993; Avise 1994; Rosenzweig 1995).
In this paper I describe one way in which species interactions operating in local communities may influence the potential for speciation by influencing the potential for generating differentiation across the range of a species as hypothesized in the allopatric speciation
model with regional differences in selection.
Lynch (1989) concluded that vicariance events occur with greater frequency than other modes of allopatric speciation
or biogeographic patterning.
In the case of hosts and parasites, for example, a speciation event within a particular host lineage might be expected to isolate the parasite population associated with each incipient host species, and thus to produce an allopatric speciation
event among parasites.
Genetic and phenotypic discontinuities within species are commonly produced by geographic barriers to dispersal (Mayr 1942), and the ultimate genetic isolation of such divided taxa, i.e., allopatric speciation
via vicariance, may be the most common way in which new species originate (Lynch 1989).
A universally accepted mechanism of speciation is allopatric speciation
(White 1978; Littlejohn and Watson 1985) or adaptive divergence (sensu Templeton 1981).
If it is not, then the possibility exists that geographic or allopatric speciation
has occurred, allowing sympatric coexistence in southern California.