62
A . R . MAIN
snout vent length. The changes in proportion of juveniles and adults
are shown in Fig. 6 for three localities on Rottnest Island, from which
it is clear that the recruitment and adult survival are not constant but
fluctuate considerably. The weather experienced during the winter
breeding season (see Table VI) may have a bearing on the age structure
of the population. The species is relatively short-lived as shown by a
sample of 312 juveniles which were individually marked in November,
1961. The following November a sample of 151 frogs yielded 22 adults,
of which only 4 were of the series of 312 marked the previous year.
1. COMMONNESS A N D RARENESS
The very general ecological problem posed by the commonness and
rareness of species can hardly be answered with the present fragmentary
knowledge of frogs. However, the following points suggest that a number of factors may contribute to rareness.
(a) Physical environment: As already noted Neobatrachus centralis,
N. sutor and N. urilswei are common where the ground waters are
saline. Only N . centratis and N . sutor are found, and are then only
rarely where Limnodynastes spenceri or Cyclorana platycephulus occur.
(b) Low fecundity: Myobatrachus gouldii is restricted to a widespread
habitat (deep sands, reliable rainfall) but is an uncommon species and
only rarely collected when deliberately sought. As the food is common
it may be assumed that t,he low fecundit,y contributes t’o low population
density.
(c) Low fecundity combined with preference for restricted minor habitats: Metacrinia nicholbi (8-12 eggs), Crinia rosea, C . lutea (both c. 30
eggs) and Fseudophyne douglasi (c. 90 eggs) appear to be examples of
this category of rareness (Main, 1957, 1963, 1964, 1965a).
The typical “common species” appears to be represented by Neobatrachzls centralis which has a wide tolerance of breeding conditions,
high fecundity, wide tolerance of physical environmental conditions as
larvae and adult, and short larval life. Nevertheless, these advantages
are insuficient to prevent relegation of the species to rareness under
Norno conditions as discussed above.
J. POLYMORPHISM
The section of the genus Crinia in which the prevomer is divided and
the belly is granular contains 10 species and of these there are 8,
namely C . signifera Girard, C. tinnula, C. patinsignifera Main, C . insignijern, C . peudinsignifera, C. subinsignifera, C . georgiana and
6 . glawrti, in which the variability of the dorsal pattern is discontinuous.
Former!y the variants of the dorsal pattern had been named rn speciea
A . R . MAIN
snout vent length. The changes in proportion of juveniles and adults
are shown in Fig. 6 for three localities on Rottnest Island, from which
it is clear that the recruitment and adult survival are not constant but
fluctuate considerably. The weather experienced during the winter
breeding season (see Table VI) may have a bearing on the age structure
of the population. The species is relatively short-lived as shown by a
sample of 312 juveniles which were individually marked in November,
1961. The following November a sample of 151 frogs yielded 22 adults,
of which only 4 were of the series of 312 marked the previous year.
1. COMMONNESS A N D RARENESS
The very general ecological problem posed by the commonness and
rareness of species can hardly be answered with the present fragmentary
knowledge of frogs. However, the following points suggest that a number of factors may contribute to rareness.
(a) Physical environment: As already noted Neobatrachus centralis,
N. sutor and N. urilswei are common where the ground waters are
saline. Only N . centratis and N . sutor are found, and are then only
rarely where Limnodynastes spenceri or Cyclorana platycephulus occur.
(b) Low fecundity: Myobatrachus gouldii is restricted to a widespread
habitat (deep sands, reliable rainfall) but is an uncommon species and
only rarely collected when deliberately sought. As the food is common
it may be assumed that t,he low fecundit,y contributes t’o low population
density.
(c) Low fecundity combined with preference for restricted minor habitats: Metacrinia nicholbi (8-12 eggs), Crinia rosea, C . lutea (both c. 30
eggs) and Fseudophyne douglasi (c. 90 eggs) appear to be examples of
this category of rareness (Main, 1957, 1963, 1964, 1965a).
The typical “common species” appears to be represented by Neobatrachzls centralis which has a wide tolerance of breeding conditions,
high fecundity, wide tolerance of physical environmental conditions as
larvae and adult, and short larval life. Nevertheless, these advantages
are insuficient to prevent relegation of the species to rareness under
Norno conditions as discussed above.
J. POLYMORPHISM
The section of the genus Crinia in which the prevomer is divided and
the belly is granular contains 10 species and of these there are 8,
namely C . signifera Girard, C. tinnula, C. patinsignifera Main, C . insignijern, C . peudinsignifera, C. subinsignifera, C . georgiana and
6 . glawrti, in which the variability of the dorsal pattern is discontinuous.
Former!y the variants of the dorsal pattern had been named rn speciea