Temporal and Spatial Variation in Egg Size and Fecundity in Rana temporaria

(1) Fecundity (number of eggs), egg size (mean egg dry mass) and clutch mass (total egg dry mass) were measured in four widely separated populations of Rana temporaria over the period 1981-84. (2) The size distributions of breeding females varied among populations and, at one site, between years. Fecundity, egg size and clutch mass were all correlated with body size. After adjusting for body size, it was found that (i) fecundity varied among populations but was consistent from year to year within populations; (ii) egg size (and consequently clutch mass) varied among populations and from year to year; (iii) egg size was negatively correlated with fecundity; (iv) clutch mass was positively correlated with fecundity. (3) The largest eggs, in absolute and relative terms, were laid at the site where spawning was earliest. Other studies have associated large egg size with late spawning at high altitude or latitude. (4) From a discussion of the results in relation to the partitioning of reproductive investment, the physiology underlying that process, and proximate environmental effects, it is concluded that (i) single years' data may not adequately describe a population's reproductive characteristics; (ii) efforts to interpret differences between the ranges of life-history traits of populations should take account of the animal's physiology-the constraints this imposes and its responses to proximate environmental factors.