Comparative demography of two giant caulescent rosettes (Espeletia timotensis and E-spicata) from the high tropical Andes

Using field data from previous studies we built matrix models for two popul ations of giant rosettes, Espeletia timotensis Cuatrec. and E. spicata Sch. Bip. Wedd., from the Andes Cordillera in Merida, Venezuela. We analysed th e models and calculated population growth rate (lambda), sensitivities, ela sticities and the sensitivity of the elasticities to changes in the vital r ates. The analysis showed that the two species behave alike in general demo graphic terms. In both models, population growth rate is positive and sensi tivities of lambda to changes in vital rates decrease markedly in this orde r: plant establishment, progression of juvenile-adult, germination and surv ival. The relative contributions of vital rates to lambda (elasticities) ar e very similar to those of other woody plant species: a higher contribution of survival and a very low contribution of fecundity. Transition from seed ling to juvenile is most important and the younger established stages (juve niles and young adults) play a predominant demographic role in both populat ions. Seed banks and older adults are playing a relatively minor role in th e dynamics of both populations. However, they may be important in relation to unpredictable, favourable or detrimental events. Perturbation analysis o f elasticities showed that increasing the rate of plant establishment will decrease the relative importance of stasis. We conclude that both species a re demographically very close, and similar to other long-lived woody plant species. However, the two species differ in the role of the seed bank, whic h seems more important in the demography of E. spicata than in E. timotensi s.