How does Merendera montana (L.) Lange (Liliaceae) benefit from being consumed by mole-voles? Daniel Gómez-García 1, *, José Azorín 1 , Stella M. Giannoni 2 and Carlos E. Borghi 2 1 Instituto Pirenaico de Ecología (CSIC), Apdo. 64, Jaca, E-22700, Huesca, España; 2 IADIZA (CONICET), GIB, CC. 507, Mendoza, 5500, Argentina; *Author for correspondence Received 19 March 2002; accepted in revised form 7 February 2003 Key words: Alkaloid concentration, Animal-plant interaction, Geophytes, Protocooperation, Subterranean rodents Abstract The relationships between a geophyte (Merendera montana (L.) Lange – Liliaceae) and a mole-vole (Microtus duodecimcostatus de Sélys-Longchamps) in the Spanish Pyrenees were investigated by analysing plant density, asexual reproductive strategies, and chemical composition of M. montana, and by observing the feeding behavior of M. duodecimcostatus in captivity. We found that M. montana contains toxic alkaloids, the concentration of which varies throughout the year; being minimal at the end of the vegetative period. Alkaloids are stored in the whole plant, particularly in the leaves which are scarcely consumed by herbivores. Nevertheless, mole-voles eat this plant profusely both in the field and in captivity, where they showed preference for the corm. The corm has lower alkaloid concentration and higher levels of energetic substances than the other plant parts, particularly leaves. Although corm consumption causes plant death, M. montana grows more abundantly in areas colonized by mole-voles than in undisturbed grasslands with high plant cover and absence of mole-vole populations. Both asexual reproduction and seedlings of this species are more frequent in highly disturbed areas. Results strongly suggest a protocooperative relationship between mole-voles and this geophyte: the burrowing behavior of mole- voles favours dispersal and reproductive success of the plant, enhancing its habitat availability; the plant in turn supplies abundant and nutritious food at a low and acceptable toxicity cost. Introduction The influence of rodents on vegetation and particu- larly on grasslands has been a much discussed topic in plant ecology (Summerhayes 1941), as was the ef- fect of disturbances caused by burrowing mammals on the structure and dynamics of plant communities (Collins and Barber 1985; Harper 1977; Hobbs and Hobbs 1987; Huntly and Inouye 1988; Hobbs and Mooney 1991; Huntly and Reichman 1994; Reich- man and Jarvis 1989; Sousa 1984). On the other hand, some relationships between a few plants and subter- ranean rodents, showing adaptive behaviors to their mutual advantage, have also been described, nearly all of them in subdesert areas of Israel and Africa (Brett 1991; Galil 1967; Lovegrove and Jarvis 1986). In recent studies of mole-voles (genus Microtus Schrank) in the Spanish Pyrenees, we showed that these burrowing animals influence plant composition, plant community structure, and seed dispersal (Gómez-García et al. 1995, 1999). Furthermore, we found a strong decrease in plant cover and dominant species coupled with an increase in geophyte abun- dance in areas inhabited by mole-voles (Gómez- García et al. 1995), which suggested some sort of relationship between these organisms. In fact, in the South of Spain, it has been found that mole-voles feed extensively on the storage organs of several geo- phytes, which can represent over 90% of their diet (Soriguer and Amat 1980). In general, geophytes contain a considerable and well-stored quantity of nutrients in the corm, which makes them an excellent food resource for many ani- mals, especially for subterranean mammals (Bennett and Jarvis 1995). Moreover, these are also asexual reproductive propagules, which, just like seeds, get 173 © 2004 Kluwer Academic Publishers. Printed in the Netherlands. Plant Ecology 172: 173–181, 2004.