RESPONSES OF A CARNIVOROUS PLANT TO PREY AND INORGANIC NUTRIENTS IN AMEDITERRANEAN ENVIRONMENT

We have analysed the effect of prey and fertilization by inorganic nut rients on the survival, growth, reproduction (sexual and vegetative) a nd mucilage secretion of Pinguicula vallisneriifolia (Lentibulariaceae ), a carnivorous plant inhabiting rocky substrates of southern Spain. We tested the hypothesis that carnivorous plants are more prey depende nt when root access to nutrients is strongly limited by (1) analysing the importance of the carnivorous habit to the fitness of P. vallisner iifolia in its natural rocky habitat, and (2) determining whether the effect of trapped prey varies with soil nutrient levels. Our 2-year ex perimental results indicated prey to be limiting to P. vallisneriifoli a growth on its natural rocky substrate. Animal food supply substantia lly increased the chance of survival, growth, vegetative propagation, sexual reproductive success and mucilage secretion. The differences be tween prey levels were more evident at the end of the experiment when all the surviving prey-exclusion plants had lost weight, and the proba bility of sexual reproduction and of vegetative propagation by axillar y buds had accordingly diminished. Furthermore, there were clear benef its from carnivory at the population level, since both the expected in dividual life span and the lifetime vegetative and sexual output corre lated positively with the quantity of prey trapped. Application of ins ects to non-fertilized plants stimulated growth, but similar applicati on to fertilized plants grown on a complete nutrient solution failed t o enhance growth. There was no obvious benefit from the provision of a balanced mineral nutrient solution (alone or with prey). The greatest absolute growth and sexual and vegetative output resulted from provid ing a surplus of insects to plants on their natural rocky substrate. T he strong dependence of P. vallisneriifolia on prey can therefore be c onsidered a useful preadaptation enabling colonization of rocky substr ates.