In the offspring size example the comparison between individuals may have been significant for mean values but these statistical differences had no apparent fitness consequences for offspring. A search of the literature shows that numerous studies have measured reproduction in woodlice, especially for temperate species, in an attampt to explain population dynamics or life history tactics. Between 1990 and 1994 we were also able to collect data on female size, fecundity, reproductive allocation and offspring size for several tropical species. Comparing these data there are several significant patterns. As well as showing a linear relationship within species and populations, fecundity also shows an allometry with female size across species.
Larger females have more offspring.
The trends across species is reversed for reproductive allocation so that in species with a small body size, females appear to invest more in each brood. Although significant, this trend across species is less convincing than the relationship for fecundity. The key comparison to assess function is between female size and offspring size. Across species offspring size is consistently between 0.2 and 0.3mg with no apparent increase over nearly three orders of magnitude in mean female mass . Notable exceptions where females produce exceptionally large offspring are Ligia oceanica , a littoral species with equally exceptional female size, and the arid zone species Armadillo officinalis .