José Ramos-Zapata

Structure of plant–Hymenoptera networks in two coastal shrub sites in Mexico

The study of interaction networks between plants and pollinators allows us to explore interaction patterns at the community level, detect changes in visit frequency and evaluate the nestedness of the networks. The latter allows rare plant species to be visited by more abundant species of pollinators, potentially allowing community diversity to be maintained, and this approach makes it possible to discern the rewiring (changes in connections) of species when their preferred resource is not available. In this study, the topology, species identity and rewiring were compared between two contrasting sites, one within a conservation area and the other subjected to continuous disturbance. The networks of both sites were significantly nested and shared a high number of common species of both plants and pollinators. However, the sites differed notably in the number of exclusive interactions, suggesting a high percentage of interaction rewiring. The introduced bee species, Apis mellifera, was the most frequent species at both sites and also the most connected in terms of the number of its interactions. This is explained by its generalist foraging characteristics that allow it to form part of the networks’ core group. In general, our results underscore the importance of knowing the identity of the participating species when studying networks, and how connections change between them, as well as the potential effect of habitat destruction and the role of invasive species in the rearrangement of the interactions; all factors that can exert an influence on the functioning of plant–pollinator networks.

Research on arbuscular mycorrhizae in Mexico: an historical synthesis and future prospects

This review analyzes the historical development and advances of the research on arbuscular mycorrhizal fungi (AMF) in Mexico, as well as the prospects for future research. AMF-research has been focused on studying both diversity and functionality in several ecosystems of Mexico, but mainly in the tropical dry and rainy ecosystems, and the agricultural systems. In Mexico, 95 species of AMF have been recorded, representing 41% of the known species worldwide. The functional effects of AMF colonization have been examined in approximately 10% of the known host plants, but greenhouse studies continue to dominate over those conducted under field conditions. Even though research to date has been at the organismic level, further effort is needed due to the high plant diversity in Mexico. Studies on AMF biomass under field conditions and more taxonomic determination are required based on morphological features, biochemical determinations (fatty acids) and molecular tools. In addition, ecophysiological and ecological in situ studies would help in understanding the relationships among AMF, soil fauna, nutrients, and host plants. The contribution of AMF to ecosystemic processes is a priority line of research that requires an integrated approach (inter- and multidisciplinary) in order to define the role of AM symbioses for biogeochemical models. The creation of a Mexican mycorrhizal research network has and will help to identify the main challenges. Generating similar research protocols, and sharing databases and experience will assist mycorrhizologists working under the diverse financial and ecological contexts that is to be found in Mexico and Latin America.

Genetic variation in the response of the weed Ruellia nudiflora (Acanthaceae) to arbuscular mycorrhizal fungi

The main goal of this work was to test for plant genetic variation in the phenotypic plasticity response of the weed Ruellia nudiflora to arbuscular mycorrhizal (AM) fungi inoculation. We collected plants in the field, kept them under homogeneous conditions inside a nursery, and then collected seeds from these parent plants to generate five inbred lines (i.e., genetic families). Half of the plants of each inbred line were inoculated with AM fungi while the other half were not (controls); a fully crossed experimental design was then used to test for the effects of treatment (with or without AM fungi inoculation) and inbred line (genetic family). For each plant, we recorded the number of leaves produced and the number of days it survived during a 2-month period. Results showed a strong positive treatment effect (plastic response to AM fungi inoculation) for leaf production and survival. Moreover, in terms of survival, the treatment effect differed between genetic families (significant genetic family by treatment interaction). These findings indicate that the positive effect of AM fungi on plant survival (and potentially also growth) differs across plant genotypes and that such condition may contribute to R. nudiflora’s capacity to colonize new environments.

Wetland plant species improve performance when inoculated with arbuscular mycorrhizal fungi: a meta-analysis of experimental pot studies

The presence of arbuscular mycorrhizal fungi (AMF) in wetlands is widespread. Wetlands are transition ecosystems between aquatic and terrestrial systems, where shallow water stands or moves over the land surface. The presence of AMF in wetlands suggests that they are ecologically significant; however, their function is not yet clearly understood. With the aim of determining the overall magnitude and direction of AMF effect on wetland plants associated with them in pot assays, we conducted a meta-analysis of data extracted from 48 published studies. The AMF effect on their wetland hosts was estimated through different plant attributes reported in the studies including nutrient acquisition, photosynthetic activity, biomass production, and saline stress reduction. As the common metric, we calculated the standardized unbiased mean difference (Hedges’ d) of wetland plant performance attributes in AMF-inoculated plants versus non-AMF-inoculated plants. Also, we examined a series of moderator variables regarding symbiont identity and experimental procedures that could influence the magnitude and direction of an AMF effect. Response patterns indicate that wetland plants significantly benefit from their association with AMF, even under flooded conditions. The beneficial AMF effect differed in magnitude depending on the plant attribute selected to estimate it in the published studies. The nature of these benefits depends on the identity of the host plant, phosphorus addition, and water availability in the soil where both symbionts develop. Our meta-analysis synthetizes the relationship of AMF with wetland plants in pot assays and suggests that AMF may be of comparable importance to wetland plants as to terrestrial plants.

Effects of arbuscular mycorrhizal fungi on above‐ground tri‐trophic interactions are contingent upon plant genetic effects of cross type in the perennial herb Ruellia nudiflora

Recent work has improved our understanding of the linkages between above- and below-ground interactions mediated by plants. However, relatively few of the studies conducted thus far have focused on multi-trophic interactions (i.e. beyond two trophic levels) and the influence of plant genetic intraspecific variation on these dynamics has rarely been addressed. We tested the effect of arbuscular mycorrhizal fungi (AMF) on above-ground tri-trophic interactions associated with the canopy of the perennial herb Ruellia nudiflora, and further determined whether genetic effects due to cross type (i.e. whether a plant originated from self- or cross-pollination) influenced these interactions. We propagated plants originating from self- or cross-pollination, and within each category inoculated half of the plants with AMF. We subsequently established a common garden where plants were exposed to naturally occurring seed-eating caterpillars and their parasitoids. We measured plant growth, fruit output, calculated the proportion of attacked fruits by the caterpillar and the proportion of parasitized caterpillars, and also estimated the proportion of “rescued” seeds by parasitoids representing an indirect positive effect of the third trophic level on the plant by reducing caterpillar consumption. Arbuscular mycorrhizal fungi drove 18% and 15% increases in plant growth and fruit output respectively, and drove a 25% reduction in caterpillar fruit attack, but did not influence parasitism or parasitoid seed “rescue.” In contrast, cross type did not influence growth, fruit number, herbivore attack, parasitism or seed rescue. More importantly, however, we found a significant AMF by cross type interaction on caterpillar attack, where AMF significantly reduced fruit attack (by 30%) in progeny from cross-pollination but did not influence herbivory in progeny from self-pollination. Synthesis. Results indicate that effects of arbuscular mycorrhizal fungi on above-ground interactions are contingent upon plant intraspecific variation originating from cross type, which is likely a common source of variation in associated interactions for plants with mixed mating systems. Further studies examining plant-mediated below- and above-ground interactions should consider the influence of specific sources of plant genetic variation, as well as address the consequences of such dynamics for interactions beyond two trophic levels.

Ecological and evolutionary consequences of tri-trophic interactions: Spatial variation and effects of plant density

PREMISE OF STUDY The factors driving variation in species interactions are often unknown, and few studies have made a link between changes in interactions and the strength of selection. METHODS We report on spatial variation in functional responses by a seed predator (SP) and its parasitic wasps associated with the herb Ruellia nudiflora. We assessed the influence of plant density on consumer responses and determined whether density effects and spatial variation in functional responses altered natural selection by these consumers on the plant. We established common gardens at two sites in Yucatan, Mexico, and planted R. nudiflora at two densities in each garden. We recorded fruit output and SP and parasitoid attack; calculated relative fitness (seed number) under scenarios of three trophic levels (accounting for SP and parasitoid effects), two trophic levels (accounting for SP but not parasitoid effects), and one trophic level (no consumer effects); and compared selection strength on fruit number under these scenarios across sites and densities. KEY RESULTS There was spatial variation in SP recruitment, whereby the SP functional response was negatively density-dependent at one site but density-independent at the other; parasitoid responses were density-independent and invariant across sites. Site variation in SP attack led, in turn, to differences in SP selection on fruit output, and parasitoids did not alter SP selection. There were no significant effects of density at either site. CONCLUSIONS Our results provide a link between consumer functional responses and consumer selection on plants, which deepens our understanding of geographic variation in the evolutionary outcomes of multitrophic interactions.