|326 HETEROCHRONY AND PAEDOMORPHOSIS
Under colonization, I link two phenomena often considered separately: the exploitation of renewed abundant resources by the survivors of an in situ population crash,4 and the chance dispersal of a few colonizing immigrants to new areas with no competitors. Both possess the common feature of presenting to a few individuals a superabundant regime of resources; r strategists should prevail in such a circumstance, since rapid increase in numbers will be so strongly favored. Progenesis represents one of the easiest and most rapid pathways to high r; it should be very common among colonizers.
My previous examples among insects all fall into this category. The newly grown mushroom and the unexploited leaf are superabundant, uncolonized resources. Wyatt (1964) presents a striking example of how effective accelerated maturation can be among the paedogenetic gall midges. Mycophila speyeri and M. barnesi infest the same beds of cultivated mushrooms. They differ in little else but their generational cycles: newly hatched M. speyeri larvae reproduce in five to six days; M. barnesi takes seven to eight days. The first flush of affected mushrooms begins five weeks after spawning, and M. speyeri can destroy up to 80 percent of it; thereafter, the density of M. speyeri falls. M. barnesi does not reach damaging density during the first flush. It may attack the second flush a week later in a moderate way, but it often destroys the third and later flushes. Wyatt (1964) attributes this difference entirely to the more rapid generation time of M. speyeri.
J. G. Blower has published several works on the correlation of progenesis and colonizing ability in myriapods. Blower and Gabbutt (1964) contrasted the life histories of Cylindroiulus punctatus and C. latestriatus. Both species reach their seventh stadium after two years. Progenetic C. latestriatus breeds in this stadium, producing about one- half as many eggs as C. punctatus, which breeds in its third year at the eighth or ninth stadium. Blower and Gabbutt assessed the relative effect of laying half as many eggs, but laying them a year earlier, by constructing theoretical curves assuming a constant mortality of 80 percent from birth to maturation. Since C. latestriatus, by this calculation, outproduces C. punctatus until the sixth year, Blower and Gabbutt felt that its superior colonizing ability could be explained by progenesis (the effect may be even more pronounced; C. punctatus probably suffers greater mortality between birth and maturity since it spends an additional year in the immature state). Blower (1969) then contrasted three pairs of related species, each containing one small progenetic form and one normal form (Brolemann, 1932, has emphasized the importance of progenesis among myriapods). In each pair, the