Modelling reproductive effort in sub-and maritime Antarctic mosses

A comparison is made of the reproductive effort (RE), considered as the investment in sporophyte relative to gametophyte biomass, of eight species of moss occurring at sub-and maritime Antarctic sites. Six of the species showed smaller sporophytes and game-tophytes at the climatically more extreme maritime Antaretic sites and one species showed no size difference between regions. The remaining species, although showing no regional difference, showed some evidence of a reverse pattern, with higher altitude samples having greater biomass than lower altitude samples. Spore counts indicated a measure of compensation in maritime Antarctic samples, with no significant decrease in spore output in several species despite smaller sporophyte biomass. The relationship between sporophyte (S) and gametophyte (G) biomass within samples was described by an allometric curve (S=aGb) which gave a better fit than a straight line for six species. This form of model allows comparisons of patterns of RE to be made between samples with non-or partially overlapping size distributions, even when the relationship involves size-dependence. An allometric curve was not appropriate for describing samples of one species (Andreaea regularis), and insufficient data were available to identify any relationship in Polytrichum alpinum. The exponent (b) differed between species, but there were no statistically significant differences between exponents from samples of the same species. Samples of two species could further be described by the same coefficient (a), indicating that they lie on the same curve. However, samples of three species from sub-Antarctic South Georgia gave significantly higher coefficients, indicating increased RE relative to maritime Antarctic populations.

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