Comparative Plant Demography--Relative Importance of Life-Cycle Components to the Finite Rate of Increase in Woody and Herbaceous Perennials

Abstract

1 Stage projection (Lefkovitch) matrices for 21 species of woody plants and 45 herbaceous perennials were extracted from the plant demographic literature or compiled from published data. 2 Each matrix was divided into six regions representing: 1, recruitment of seeds to the seed pool; 2, recruitment of seedlings or juveniles from current seed production; 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 X for each population and to calculate the elasticities of each transition coefficient in the matrices. Elasticities were summed within each of the six regions of the matrix to give measures (E1 -E69 respectively) of the importance of each component of the life cycle to X and fitness. 4 Herbs as a group differed significantly from woody plants in most of these components. Seedling recruitment was more important in herbs than woody plants. Retrogression occurred only in herbs, particularly those with a tuber. Stasis occurred in nearly all species, but was most important in woody plants. Progression was more important than fecundity in almost all species. 5 Trade-offs among life cycle components were determined from correlation matrices of r (= ln X) and elasticities E1 -E6 for the whole sample and for herbs and woody plants separately. As a whole, r was positively correlated with elasticities for fecundity (E1 + E2) and growth (E3 + E6) and negatively correlated with survival (E4 + E15). In clonal herbs, fecundity and clonal 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 plots in G-L-F space. This was done separately for iteroparous forest herbs, 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 the end of the distribution with the lowest survival elasticity. 7 It is argued that the demographic approach to the classification of distinct ecological groups offers new insights into the relationship between life history and habitat.

Demographic response to shading and defoliation in two woodland orchids

“…In the present study, keeping more ramets of lower quality may increase the chance of photosynthesizing by reducing the chance of complete defoliation and/or shading. This condition may represent bet-hedging, in which the variability in photosynthesis from year-to-year is reduced in order to maximize survival, and hence fitness (SILVERTOWN et al 1993, SLATKIN 1974, STUEFER et al 1996. This further suggests that there may be a threshold level of acquired and stored resources that may be needed to sprout at all.…”

“…The fitness of long-lived organisms is most sensitive to changes in adult survival (SILVERTOWN et al 1993, SATHER & BAKKE 2000, and adult survival in such organisms is generally invariant (GAILLARD & YOCCOZ 2003), suggesting that it has a higher priority than reproduction in resource allocation (GLAZIER 2002). Furthermore, in clonal plants, adult survival is a function of growth, suggesting that any life history trade-offs with growth will also affect plant survival (CHESSON & PETERSON 2002).…”

Effects of sheep grazing and temporal variability on population dynamics of the clonal herb Geranium sylvaticum in an alpine habitat

“…2; cf. Silvertown et al 1993): fecundity (F recruitment of seedlings from the seed production); clonal reproduction (C recruitment of clonal offspring); growth (G transitions to a larger life-stage class); stasis (S survival in the same life-stage class, including survival of clonal offspring) and retrogression (R transitions to a smaller life-stage class or to dormancy).…”

Reprodução sexuada de Dyckia tuberosa (Vell.) Beer (Bromeliaceae, Pitcairnioideae) e interação planta-animal

“…Em espécies vegetais é comum ocorrer a combinação entre dois modos de reprodução: via produção de sementes, normalmente envolvendo a fusão de gametas, e via propagação clonal (Richards 1997). Quando o recrutamento de indivíduos via produção de sementes é pequeno ou ausente, a propagação clonal pode ser suficiente para manter o crescimento populacional (Eriksson 1993, Silvertown et al 1993. Segundo Benzing (2000), o ciclo de vida de espécies de Bromeliaceae geralmente é lento, sendo necessários vários anos para que um indivíduo se reproduza sexuadamente.…”