Plant Ecology & Diversity iFirst, 2011, 1–11 REVIEW ARTICLE Ecology and evolution of negative and positive interactions in Cactaceae: lessons and pending tasks Pablo C. Guerrero a *, Gastón O. Carvallo b , Jafet M. Nassar c , Julissa Rojas-Sandoval d , Virginia Sanz c and Rodrigo Medel e a Instituto de Ecología y Biodiversidad (IEB), Universidad de Chile, Santiago, Chile; b Instituto de Biología, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile; c Instituto Venezolano de Investigaciones Científicas, Altos de Pipe, Estado Miranda, Venezuela; d Center for Applied Tropical Ecology and Conservation, San Juan, Puerto Rico; e Departamento de Ciencias Ecológicas, Universidad de Chile, Santiago, Chile (Received 27 January 2011; final version received 3 October 2011) Background: The Cactaceae is a diverse and conspicuous Neotropical family that has evolved a wide variety of adaptations during co-evolution with their interacting species. Recent research has indicated complex ecological and evolutionary inter- actions involving cacti and other organisms. Aims: We reviewed four studies involving cacti that have important implications for our understanding of the evolution of life traits and maintenance of cactus diversity. Also, these studies illustrate how the modern theoretical background of the ecology and evolution of species interactions is influencing the research in Cactaceae. Methods: The studies showed here are (1) the evolutionary ecology of a mistletoe-cactus parasitism in central Chile, (2) the effect of an exotic grass on the demography of a threatened cactus in Puerto Rico, (3) the herpetochory in a tropical genus of cacti in Venezuela, and (4) the role of abiotic and biotic factors on the floral morphology in globose cacti species in northern Chile. Results: The parasitic interaction between the mistletoe and a columnar cactus highlights the importance of spine length as a defensive co-evolving trait. Reproductive success in the endemic cactus in Puerto Rico was depressed by the presence of the exotic grass. Lizards actively fed on fruits of a tropical group of cacti, increasing the germination percentages of seeds. Climatic gradients might induce morphological change in the flowers of Mediterranean cactus species. Conclusions: Interactions involving cacti reflect a complex scenario of ecological and evolutionary processes which may account for several patterns of the diversity of Cactaceae. In this sense, to enhance the on-going research, we emphasise the necessity of the development of a cactus interaction database; the assessment of detrimental effects of invasive species on cactus diversity; and the quantification of multi-species interactions. Keywords: American continent; Caribbean; climatic drivers; grass invasion; parasitism; pollination; seed dispersal; succulent Introduction The Cactaceae, with more than 1600 recognised species, is one of the most conspicuous and diverse Angiosperm families in the Neotropics (Anderson 2001). Although mostly restricted to arid and semi-arid ecosystems, the family is almost continuously distributed in North and South America and the Caribbean, from southern Canada to Patagonia, across a wide range of vegetation types (e.g. tropical and temperate forests, Andean high-altitude veg- etation and deserts). The role of cacti in the maintenance of ecosystem functioning, and the long history of their use by humans in their cultural practices, has resulted in the recognition of the importance of these plants for ecosystem services, especially in arid climates (Nobel 2002; Ashworth et al. 2009). As a result of the inherent complexity of the evolu- tionary trajectory of the family in different habitats and communities, cacti have developed a broad spectrum of positive and negative ecological interactions with diverse groups of organisms. The framework provided by ecolog- ical interactions, antagonistic or mutualistic, enables the study of the extent to which the current diversity of life has *Corresponding author. Email: pablo.c.guerrero@gmail.com resulted from reciprocal adaptive adjustments (e.g. mor- phological traits) in multi-species and complex ecological scenarios (Levey et al. 2002; Thompson 2005; Morand and Krasnov 2010). With regard to cacti, a number of recent studies have provided new perspectives on the role of mutualistic and antagonistic interactions in demographic and evolutionary phenomena (e.g. Holland and DeAngelis 2001; Nobel 2002; Fleming and Valiente-Banuet 2002; Wolf and Martínez del Río 2003; Ritz et al. 2007; Fleming et al. 2009; Schlumpberger et al. 2009; Castillo-Landero and Valiente-Banuet 2010; Medel et al. 2010). Positive interactions involving cacti have received far more attention than negative ones. Probably most, if not all, cactus species are involved in pollination or seed dispersal mediated by animals (Valiente-Banuet et al. 1997a, 1997b; Fleming et al. 2001; Fleming and Valiente-Banuet 2002), sometimes evolving extreme obligate mutualisms, such as in the case of the senita cactus Lophocereus schotti Engelm. Britton & Rose, exclusively pollinated by the senita moth Upiga virescens Hulst in the Sonoran desert (Holland and Fleming 1999). Cacti also offer other less-explored benefits to other plants by acting as nurse species (Valiente-Banuet ISSN 1755-0874 print/ISSN 1755-1668 online © 2011 Botanical Society of Scotland and Taylor & Francis http://dx.doi.org/10.1080/17550874.2011.630426 http://www.tandfonline.com Downloaded by [Universidad de Chile], [Pablo C. Guerrero] at 10:52 06 January 2012