Roger Guevara

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Local extinctions have cascading effects on ecosystem functions, yet little is known about the potential for the rapid evolutionary change of species in human-modified scenarios. We show that the functional extinction of large-gape seed dispersers in the Brazilian Atlantic forest is associated with the consistent reduction of the seed size of a keystone(More)
The hypothesis that plant species are more responsive to mycorrhiza in late than in early successional stages was assessed in grasses from a successional process occurring in two-phase mosaics from the Mexican Chihuahuan Desert. We estimated the density of spores of arbuscular mycorrhizal (AM) fungi and the AM colonization of pioneer and late-successional(More)
B. Ruiz-Guerra (bruiz@ecologia.unam.mx), Depto de Ecologı́a Evolutiva, Inst. de Ecologı́a, UNAM, AP 70-275, 04510 D.F., Mexico. R. Guevara, Depto de Ecologı́a Evolutiva. Inst. de Ecologı́a AC. Km 2.5 carretera antigua a Coatepec 351, MX 91070 Xalapa, México. N. A. Mariano, Depto de Ecologı́a, Centro de Educación Ambiental e Investigación Sierra de Huautla,(More)
Gradient analysis is rarely used in studies of fungal communities. Data on macromycetes from eight sites along an elevation gradient in central Veracruz, Mexico, were used to demonstrate methods for gradient analysis that can be applied to studies of communities of fungi. Selected sites from 100 to 3,500 m altitude represent tropical dry forest, tropical(More)
BACKGROUND Functional redundancy has been debated largely in ecology and conservation, yet we lack detailed empirical studies on the roles of functionally similar species in ecosystem function. Large bodied frugivores may disperse similar plant species and have strong impact on plant recruitment in tropical forests. The two largest frugivores in the(More)
Species that are strong interactors play disproportionately important roles in the dynamics of natural ecosystems. It has been proposed that their presence is necessary for positively shaping the structure and functioning of ecosystems. We evaluated this hypothesis using the case of the world's largest parrotfish (Bolbometopon muricatum), a globally(More)
Positive density-dependent seed and seedling predation, where herbivores selectively eat seeds or seedlings of common species, is thought to play a major role in creating and maintaining plant community diversity. However, many herbivores and seed predators are known to exhibit preferences for rare foods, which could lead to negative density-dependent(More)
The different resource demands on male and female plants of dioecious species can lead to secondary sexual dimorphisms. Male and female plants might also interact differently with antagonists and mutualists. We used a repeated measures natural experiment in five subpopulations to investigate secondary sexual dimorphism in Carica papaya including(More)
Arbuscular mycorrhizal colonization in strangler figs, spore richness, and abundance of arbuscular mycorrhizal fungi were quantified in epiphytic and ground-rooted trees in a Sabal palmetto woodland that had marked heterogeneity in rooting environments for hemiepiphytic plants. An inoculation experiment was performed to assess whether low spore density(More)