Reproductive allocation in flowering plants
The proportion of resources which an organism devotes to reproduction has been assumed to be of great evolutionary and ecological significance. However, in previous studies of reproductive allocation (RA) in plants, there has been no consensus of precisely what is being measured nor how it should be measured. An attempt was made to determine the 'best' method of measuring RA and then apply this to a range of species with differing ecological strategies. Under nutrient stress caused by a low N treatment Taraxacum officinale and Poa annua were found to maintain their RA despite up to 4 fold reductions in biomass. Under K and P deficient conditions there was a preferential allocation of these elements to reproductive structures in Taraxacum. Ruderal plants therefore, seem to maintain biomass RA and seed quality despite nutrient stress. Although the nutrient RA in Taraxacum was found to be significantly different from biomass RA (KRA = 71% PRA = 66% BRA= 51.7%) the extent of the difference varied between treatments. There was therefore no obvious alternative currency to biomass. The evolutionary consequences of reproduction may also be measured through a reproductive cost which may take the form of reduced future reproduction, survival or growth. Prevention of flowering in Digitalis purpurea resulted in an increase in the number of axillary buds produced, Similarly in Plantago lanceolata removal of flowers resulted in a 3 fold increase in production of buds. In both species realisation of a reproductive cost was prevented. The importance of individual variability was noted. The importance of plant morphology was evident and was used to explain some of the anomalous RA values in the comparative experiment. RA values were collected for 40 species of Gramineae. RA was a useful ecological index which emphasised the ruderal element of a plant's strategy. When used in conjunction with other parameters particularly Rmax, RA produced a meaningful classification of species in terms of their ecological strategy.