Over the entire 1998 flowering period, individual plants differed across two orders of magnitude in the number of pods they produced, ranging from one to 270 (Table 1). The considerable interplant differences within individual elevation stations accounted for 72% of the variation in pod production in the experiments, although significant differences among elevation stations were still found (F4,102 = 7·63, P < 0·001, anova on log-transformed number of pods per plant). There was no significant trend with elevation in either the mean or variance in pod production, and no correlation between mean pod production at a station and interplant variation (rs = 0·021, df = 4, P > 0·1; Table 1). The number of seeds per pod ranged from one to 19 (Table 1) and varied significantly both within and among stations (nested anova: within station, F20,75 = 4·45, P < 0·001; among station, F4,20 = 11·28, P < 0·001), with 41·9 and 27·7% of variation explained within and among stations, respectively). There was no significant trend with elevation in either the mean or variance in seed number per pod, and no correlation between mean pod production at a station and interplant variation (rs = 0·009, df = 4, P > 0·1). Seed mass varied significantly within and between stations (nested anova: within station, F36,399 = 21·99, P < 0·001; among station, F3,399= 56·22, P < 0·001), with 60·0 and 13·0% of variation explained within and among stations, respectively. Seed mass distributions were all positively skewed, which was attributable to one or a few large-seeded individuals in each population (Fig. 1). A significant trend of heavier seeds at higher elevations was found (rs = 0·955, df = 4, P < 0·01; Table 1; Fig. 1). Although the coefficients of variance (CV) did not differ significantly among stations (Kruskall–Wallis df = 4, χ2 = 5·051, P > 0·1), the range in seed mass (as described by the ratio of largest to smallest seed) declined progressively from almost 12 at Durham City to less than 2 at Dun Fell (Table 1). Overall, the highest population variation in reproductive traits was found in the number of pods per plant, and the least in individual seed mass.
Figure 1. Histograms of seed mass distributions at each of five elevation stations. Each shading pattern refers to the seed mass distribution of an individual plant, facilitating comparisons of both population and individual seed mass distributions. Values of skew are 0·255, 0·415, 1·083, 1·004 and 0·475 for Washington, Durham, Wolsingham, Westgate and Rookhope, respectively (too few seeds were produced at Dun Fell to merit plotting).
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