We examine the same spawning-per-recruit measures as in our previous paper (Alonzo and Mangel, 2004) and compare the results of the patterns of sex change considered here with one another and with a hypothetical dioecious species, where sex is determined stochastically at birth and the primary sex ratio is fixed.
However, even a stock exhibiting the reproductive sucess rule has dynamics that are distinctly different from those of a dioecious species because a change in the size distribution of the population due to size-selective fishing is predicted to have a large effect on the productivity and sex ratio of the protogynous population.
Plasticity is not predicted to yield populations that have stock dynamics that are identical to those of dioecious species, and the performance of spawning-per-recruit measures and the relationship between egg production and population size differed greatly between all four patterns of sex change, despite the fact that the basic patterns of growth, survival, and fecundity where identical between all the scenarios considered.
Table 1 A Family Level Comparison Between the Number and Type of Dioecious Species
that have been Studied and those that Exist All dioecy Studied P=0.
At one extreme, the complete removal of males from the population would cause a stock to crash, potentially making sex-changing species more vulnerable than dioecious species in the face of high fishing pressures.
The percent drop in population size and fertilized egg production is predicted to be much greater in dioecious species and occurred more quickly than in the sex-changing stock because of a reduction in overall population fecundity even in the absence of decreased fertilization rates.
total of 23 monoecious or dioecious species with differential rewards in
and dioecious species produce larger male flowers and/or have males that
forest genus could show dioecious species in other biomes (Arroyo,
Overall, dioecious species account for approximately 7 percent of
are also very rare in southwestern Western Australia (McComb, 1966).
Dioecious species are included in the dicot genera Coprosma, Fagara, Pernettya, and Robinsonia; Juania is the only dioecious monocot in the archipelago.
Monoecious species are mostly perennial herbs or trees; all dioecious species are woody.
We believe that both mechanisms have produced dioecious species but that the two mechanisms have their greatest impact in different historical contexts and operate in different ecological and pollination syndromes.
Inbreeding avoidance is therefore unlikely to be the primary selective force behind the appearance of dioecy for most dioecious species (but see below).