Seed size, number and strategies in annual plants: a comparative functional analysis and synthesis.

BACKGROUND AND AIMS Plants depend fundamentally on establishment from seed. However, protocols in trait-based ecology currently estimate seed size but not seed number. This can be rectified. For annuals, seed number should simply be a positive function of vegetative biomass and a negative one of seed size. METHODS Using published values of comparative seed number as the 'golden standard' and a large functional database, comparative seed yield and number per plant and per m2 were predicted by multiple regression. Subsequently, ecological variation in each was explored for English and Spanish habitats, newly-calculated CSR strategies and changed abundance in the British flora. KEY RESULTS As predicted, comparative seed mass yield per plant was consistently a positive function of plant size and competitive ability and largely independent of seed size. Regressions estimating comparative seed number included, additionally, seed size as a negative function. Relationships differed numerically between regions, habitats and CSR strategies. Moreover, some species differed in life history over their geographical range. Practically, comparative seed yield per m 2 was positively correlated with FAO crop yield, and increasing British annuals produced numerous seeds. Nevertheless, predicted values must be viewed as comparative rather than absolute: they varied according to the 'golden standard' predictor used. Moreover, regressions estimating comparative seed yield m -2 achieved low precision. CONCLUSIONS For the first time, estimates of comparative seed yield and number for over 800 annuals and their predictor equations have been produced and the ecological importance of these regenerative traits has been illustrated. 'Regenerative trait-based ecology' remains in its infancy with work needed on determinate versus indeterminate flowering ('bet-hedging'), C-S-R methodologies, phylogeny, comparative seed yield per m 2 and changing life-history. Nevertheless, this has been a positive start and readers are invited to use estimates for >800 annuals, in the Supplementary Data, to help advance 'regenerative trait-based ecology' to the next level.