Morphological and physiological correlates of niche breadth in two species of Espeletia (Compositae) in the Venezuelan Andes

Abstract

We compared adaptive strategies in two plants of Venezuelan páramos (alpine areas): the widely distributed, caulescent, and pubescent Espeletia schultzii Wedd. with the acaulescent, nearly glabrous E. atropurpurea A.C. Smith which is restricted to mesic sites just above treeline. Both species occur together at 3,450 m, near treeline.Physiologically, E. schultzii was more drought resistant than E. atropurpurea, and was better adapted for carbon dioxide fixation under low temperatures. The densely pubescent leaves of E. schultzii are highly reflective; this increases the intensity of light needed for photosynthetic saturation and influences leaf temperature. Leaf pubescence may reduce the level of insect predation.Measurements of leaf productivity indicate higher values for E. atropurpurea during the rainy season and higher values for E. schultzii during the dry season. However, annual values of leaf productivity are similar for both species.Benefits of specialization in E. atropurpurea include reduced costs for stem and leaf hair production, higher growth rates during the rainy season and the ability to grow beneath canopies of some larger arborescent species. Costs of specialization include lower growth rates during the dry season, great susceptibility to insect predation and restriction to low elevation, mesic sites.

Growth and Population Dynamics of Espeletia (Compositae) in the Venezuelan Andes

“…In a second acaulescent species investigated, E. atropurpurea, a similar pattern was observed. In this species, however, new rosettes sprout from the old rosette base (see Baruch and Smith, 1979).…”

“…A study plot was established in such a population (Mucubaji), approximately 300 m from the main topographic site used for E, schultzii and a few meters above the E. schuftzii plot located on talus. An acaulescent, glabrous-leaved species, E. atropurpurea, was studied at La Aguada, a station on the Merid a Teleferico (cable car) at 3400 m. Data on this species are presented elsewhere (Baruch and Smith, 1979).…”

“…comm., March 1973). The arborescent type was apparently ancestral to the more compact caulescent rosette form, which requires lower energy allocation for nonphotosynthetic support tissue and provides greater buffering against intense diurnal temperature fluctuations (Smith, 1974a(Smith, , 1974b(Smith, , 1979. The arborescent form persists in Espeletia species of subalpine forests.…”

Water relations and gas exchange in Coespeletia moritziana (Sch. Bip) Cuatrec., a giant rosette species of the high tropical Andes

“…in the Venezuelan Andes. Baruch (1979) reports  L min of -1.5 MPa for E. schultzii adult plants at 4,200 m. These authors also describe that a severe stomatal control was necessary to maintain these high Ψ L . Estrada et al (1991) describe  L min for Coespeletia spicata of -1.6 MPa and -1.4 MPa for adult and juvenile plants, respectively, and values above -1.0 MPa for both adult and juveniles of Coespeletia timotensis in the same region of the Andes in which our study was carried out.…”

“…Both of these responses result in the maintenance of high Ψ L throughout the year with the accompanying cost in reductions of net photosynthetic rates. Low net photosynthetic rates were described for Andean giant rosette species (Baruch 1979, Baruch and Smith 1979, Goldstein et al 1989, Rada et al 1998. Schulze et al (1985) described relatively high net photosynthetic rates for different giant rosette species of the Afroalpine vegetation.…”