FITNESS RESPONSES OF A CARNIVOROUS PLANT IN CONTRASTING ECOLOGICAL SCENARIOS

This paper reports the results of a two-year field experiment on the d eterminants of fitness responses in Pinguicula vallisneriifolia (Lenti bulariaceae), an endemic carnivorous plant of southeastern Spain. For the first time, in this experiment, we have considered irradiance as a factor, in combination with animal prey, for an array of natural fiel d conditions. The goal was to determine how carnivory translates to fi tness within different radiation regimes. For this, it was necessary t o quantify an array of plant responses, such as survival, growth, repr oduction (sexual and vegetative reproduction), as well as responses re lated to carnivory investment (leaf shape and mucilage secretion). Bot h irradiance and animal food supply proved to be important limiting fa ctors for P. vallisneriifolia under field conditions. Plants clearly d ecreased in performance from the sunny habitat to the deep-shade one, with plants growing in the least irradiance registering the lowest val ues for all variables analyzed. The dearest response to prey was the p roduction of axillary buds. Most vegetative acid reproductive response s depended heavily on the initial biomass of the plant before the expe riments, the largest plants bearing the most leaves, flowers, stolons, and axillary buds. A gradient from less to more mucilage secretion ap peared from deep-shade to sunny habitat, and within each habitat from prey exclusion to prey addition levels. Trapped prey stimulated digest ive secretions in a positive feedback (the more prey, the more mucilag e secretion) under all irradiance conditions. The curled, more secreto ry leaves of the sunny plants, in comparison with the nearly flattened , less secretory leaves of the deep-shade plants, illustrate the const raints imposed by differing scenarios on the capture of both prey and photons. With nonlimiting water availability, more irradiance and prey results in more survival, growth, and sexual and vegetative reproduct ion. Nevertheless, it is not usual to find an optimum combination of r esources (i.e., irradiance, prey, and water) available in the same mic rohabitat during the Mediterranean summer. The spatial uncoupling of l imiting resources progressively increased towards the extremes of the irradiance gradient (sunny and deep-shade habitats, respectively), and therefore the dual photosynthetic and carnivore functions of P. valli sneriifolia leaves were not equally efficient in all habitats. These o pposing resource gradients determined all vegetative and reproductive plant responses. The perennial character of this endemic plant, togeth er with its vegetative form of propagation, allows the possibility of resisting extinction even in the absence of seedling recruitment or wh en vegetative growth is strongly limited.