COMPARATIVE PLANT DEMOGRAPHY - RELATIVE IMPORTANCE OF LIFE-CYCLE COMPONENTS TO THE FINITE RATE OF INCREASE IN WOODY AND HERBACEOUS PERENNIALS

1 Stage projection (Lefkovitch) matrices for 21 species of woody plant s and 45 herbaceous perennials were extracted from the plant demograph ic literature or compiled from published data. 2 Each matrix was divid ed into six regions representing: 1, recruitment of seeds to the seed pool; 2, recruitment of seedlings or juveniles from current seed produ ction; 3, clonal growth; 4, retrogression, due to plants decreasing in size or reverting in stage; 5, stasis, (survival from one year to the next in the same stage class); 6, progression to later stage classes. 3 Matrix analysis was used to calculate the finite rate of increase l ambda for each population and to calculate the elasticities of each tr ansition coefficient in the matrices. Elasticities were summed within each of the six regions of the matrix to give measures (E1 - E6, respe ctively) of the importance of each component of the life cycle to lamb da and fitness. 4 Herbs as a group differed significantly from woody p lants in most of these components. Seedling recruitment was more impor tant in herbs than woody plants. Retrogression occurred only in herbs, particularly those with a tuber. Stasis occurred in nearly all specie s, but was most important in woody plants. Progression was more import ant than fecundity in almost all species. 5 Trade-offs among life cycl e components were determined from correlation matrices of r (= In lamb da) and elasticities E1 - E6 for the whole sample and for herbs and wo ody plants separately. As a whole, r was positively correlated with el asticities for fecundity (E1 + E2) and growth (E3 + E6) and negatively correlated with survival (E4 + E5). In clonal herbs, fecundity and cl onal growth were negatively correlated. 6 The division of elasticities into three major components (growth, G = E3 + E6; fecundity, F = E1 E2; and survival, L = E4 + E5) allowed us to construct triangular plo ts in G-L-F space. This was done separately for iteroparous forest her bs, iteroparous herbs from open habitats, semelparous herbs and woody plants. Each of these four groups occupied a distinct position in G-L- F space. Within woody plants, shrubs of fire-prone habitats occupied t he end of the distribution with the lowest survival elasticity. 7 It i s argued that the demographic approach to the classification of distin ct ecological groups offers new insights into the relationship between life history and habitat.