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Species contribute differently to the structure and stability of networks of interacting species. However, species contributions to the importance of other species is usually neglected, thus limiting our understanding of species dynamics beyond the general network structure. We combined knowledge on diversity effects on focal species and network ecology to analyze the influence of plants and herbivores on big-leaf mahogany's (Swietenia macrophylla) importance in the plant–herbivore network. To this end, we built interaction networks using information from a large-scale tree diversity experiment and performed computer simulations of species removal with redistribution of interactions. We compared the importance of big-leaf mahogany in the observed networks to simulated networks where we removed: (a) tree species with similar beetle assemblages to mahogany, (b) the most interconnected (core) tree species and (c) the core beetle species. Removal of the core and similar tree species increased the importance of mahogany, whereas eliminating core beetle species decreased it. Interestingly, the effect of core tree species on mahogany’s importance was mediated by core beetles (R2 = 0.46). Neither tree nor core beetle species’ effects were contingent on tree species richness or abundance. These results indicate that highly connected tree and herbivore species jointly determine the role of mahogany in the plant–herbivore network. Likewise, these results provide insight into the effect of tree species composition and highly interactive herbivores in shaping the role of species in the herbivore network. CONACyT grant awarded to VPT and LAR (128856).

Background. The productive variability of the forage is determined by the type of soil and the cultivation system. The use of silvopastoral systems represents an alternative because they can increase forage production and quality. Objective. To evaluate the production, the morphological components and the nutritional quality of the biomass of Cynodon plectostachyus (star grass) alone or in association with Leucaena leucocephala (huaxin). Methodology. The study was carried out in Tizimin, Yucatan, Mexico. Plots of C. plectostachyus were established in alleys croping of L. leucocephala and in monoculture, in hyperskeletal Luvisols and Leptosols soils. A 2 X 2 factorial design with five repetitions per treatment was used. The biomass production, the forage components and the content of crude protein and neutral detergent fiber were evaluated for one year. Results. Forage production, leaf and forage quality did not change according to the cultivation system (p≥0.05). No effect is believed due to the type of soil (p≥0.05). The interaction of the cultivation system with the type of soil increased the NDF content of C. plectostachyus (p≤0.05). Implications. The association of C. plectostachyus and L. leucocephala could increase the availability of structural carbohydrates for ruminant nutrition. Likewise, it is essential to consider long-term evaluations that allow to know the improvements in the crude protein content and the biomass production of the grasses in association under silvopastoral systems. Conclusions. The association of C. plectostachyus with L. leucocephala in Leptosol soil increases the availability of structural carbohydrates by increasing the stem and dead tissue that can be incorporated as organic matter in the soil.

The main constraints in the ruminant production systems in the tropics are low availability and quality of forage during the dry season. An alternative that could mitigate the lack of food during periods of scarcity is the use of trees/shrubs in fodder banks. However, the growth and production response of these plants may be influenced by several factors. The aim of the study was to evaluate the total height of plants, forage yield and crude protein (CP) concentration of Morus alba and Gliricidia sepium in mixed and pure fodder bank systems with three planting densities (i.e., 10,000, 13,333 and 20,000 plants ha−1). A completely randomized design with a 3 × 3 factorial arrangement was used, with four replicates per treatment. The total height of plants was similar among fodder banks. However, G. sepium and mixed fodder banks had a greater forage yield (5.48 and 5.50 t DM ha−1, respectively) and more CP concentration (20.07 and 20.41%, respectively) than M. alba fodder banks. There was no significant effect of planting densities on total height of plants, forage yield and CP concentration, in fodder bank systems. There was no significant effect of interaction between fodder banks and planting densities on total height of plants and forage yield. However, the CP concentration was greater in the M. alba and mixed fodder banks in three planting densities, together with G. sepium fodder bank in a density of 10,000 plants ha−1, compared to G. sepium fodder banks at planting densities of 13,333 and 20,000 plants ha−1. We conclude that the mixed fodder bank of M. alba and G. sepium can increase the production and forage quality of the system.

Simple Summary Methane produced by enteric fermentation contributes to the emission of greenhouse gases (GHG) into the atmosphere. Methane is one of the GHG arising from anthropogenic activities with the greater contribution to global warming. This paper provides a brief introduction to the potential use of tropical foliage trees, pods, and secondary metabolites to reduce methane emissions from ruminant supply chains. A better knowledge of the available strategies for efficient foliage use in the tropics is essential in order to ensure increasing livestock production while preserving the environment. The mitigation of rumen methane production through the use of the foliage and metabolites of tropical trees represents an interesting challenge for scientists working in the field of ruminant nutrition. Abstract Methane produced by enteric fermentation contributes to the emission of greenhouse gases (GHG) into the atmosphere. Methane is one of the GHG resulting from anthropogenic activities with the greater global warming contribution. Ruminant production systems contribute between 18% and 33% of methane emissions. Due to this, there has been growing interest in finding feed alternatives which may help to mitigate methane production in the rumen. The presence of a vast range of secondary metabolites in tropical trees (coumarins, phenols, tannins, and saponins, among others) may be a valuable alternative to manipulate rumen fermentation and partially defaunate the rumen, and thus reduce enteric methane production. Recent reports suggest that it is possible to decrease methane emissions in sheep by up to 27% by feeding them saponins from the tea leaves of Camellia sinensis; partial defaunation (54%) of the rumen has been achieved using saponins from Sapindus saponaria. The aim of this review was to collect, analyze, and interpret scientific information on the potential of tropical trees and their secondary metabolites to mitigate methane emissions from ruminants.

Animal pollination is responsible for the majority of the human food supply. Understanding pollination dynamics in agricultural systems is thus essential to help maintain this ecosystem service in the face of human disturbances. Surprisingly, our understanding of plant–pollinator interactions in widely distributed smallholder agricultural systems is still limited. Knowledge of pollination dynamics in these agricultural systems is necessary to fully assess how human disturbances may affect pollination services worldwide. In this study, we describe the structure of a plant–floral visitor network in a smallholder Cucurbitaceae agricultural system. We further identify the main floral visitors of these crops and tested their importance by simulating how their extinction affected network structure and robustness. The observed network was highly connected and generalized but it was neither nested nor compartmentalized. Our results suggest that the structure of agricultural plant–pollinator networks could be inherently different from those in natural communities. These differences in network structure may reflect differences in spatial distribution of floral resources between agricultural and natural systems. We identified Augochlora nigrocyanea and Peponapis limitaris as the two most frequent floral visitors. However, removal of these species did not affect network structure or its robustness, suggesting high levels of interaction rewiring. To our knowledge, this is one of the first studies to describe the structure of a plant–floral visitor network in diverse agricultural systems in the tropics. We emphasize the need for more studies that evaluate network structure in agricultural systems if we want to fully elucidate the impact of human disturbances on this key ecosystem service.

The interactions between pairs of native and alien plants via shared use of pollinators have been widely studied. Studies of invasive species effects at the community level on the other hand are still scarce. Few community level studies, however, have considered how differences in the intensity of invasion, and degree of floral trait similarity between native and invasive species, can mediated effects on native plant-pollinator communities. Here, we evaluated the effect of alien species on overall plant-pollinator network structure, and species-level network parameters, across nine coastal communities distributed along 205 km at Yucatán, México that vary in alien species richness and flower abundance. We further assessed the effect of alien plant species on plant-pollinator network structure and robustness via computational simulation of native and invasive plant extinction scenarios. We did not find significant differences between native and alien species in functional floral phenotypes, the visitation rate and species composition of the pollinator community. Variation in the proportion of alien plant species and flower abundance across sites did not affect plant-pollinator networks structure. Species-level network parameters (i.e., normalized degree and nestedness contribution) did not differ between native and alien species. Furthermore, our simulation analyses revealed that alien species are functionally equivalent to native species and contribute equally to network structure and robustness. Overall, our results suggest that alien species are well integrated into native coastal plant-pollinator networks which may be facilitated by high levels of floral trait similarity and pollinator use overlap. As a result, alien species may play a similar role than that of natives in the structure and stability of native plant and pollinator communities in the studied coastal sand dune ecosystem.

Despite potential interactive effects of plant species and genotypic diversity (SD and GD, respectively) on consumers, studies have usually examined these effects separately. We evaluated the individual and combined effects of tree SD and mahogany (Swietenia macrophylla) GD on the arthropod community associated with mahogany. We conducted this study within the context of a tree diversity experiment consisting of 74 plots with 64 saplings/plot. We sampled 24 of these plots, classified as monocultures of mahogany or polycultures of four species (including mahogany). Within each plot type, mahogany was represented by either one or four maternal families. We surveyed arthropods on mahogany and estimated total arthropod abundance and species richness, as well as abundance and richness separately for herbivorous and predatory arthropods. Overall tree SD and mahogany GD had positive effects on total arthropod species richness and abundance on mahogany, and also exerted interactive effects on total species richness (but not abundance). Analyses conducted by trophic level group showed contrasting patterns; SD positively influenced herbivore species richness but not abundance, and did not affect either predator richness or abundance. GD influenced predator species richness but not abundance, and did not influence herbivore abundance or richness. There were interactive effects of GD and SD only for predator species richness. These results provide evidence that intra- and inter-specific plant diversity exert interactive controls on associated consumer communities, and that the relative importance of SD and GD may vary among higher trophic levels, presumably due to differences in the underlying mechanisms or consumer traits.

Oikos 000: 001–009, 2015 doi: 10.1111/oik.02033 © 2015 Th e Authors. Oikos © 2015 Nordic Society Oikos Subject Editor: Martijn Bezemer. Editor-in-Chief: Dries Bonte. Accepted 13 January 2015 Comparison of tree genotypic diversity and species diversity effects on different guilds of insect herbivores Luis Abdala-Roberts , Kailen A. Mooney , Teresa Quijano-Medina , Mar i a Jos e Campos-Navarrete , Alejandra Gonz a lez-Moreno and V i ctor Parra-Tabla L. Abdala-Roberts (labdala@uci.edu) and K. A. Mooney, Dept of Ecology and Evolutionary Biology, Univ. of California, Irvine, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA. – LAR, M. J. Campos-Navarrete and V. Parra-Tabla, Depto de Ecolog i a Tropical, Campus de Ciencias Biol o gicas y Agropecuarias, Univ. Aut o noma de Yucat a n, Apartado Postal 4-116, Itzimn a , MX-97000 M e rida, Yucat a n, M e xico. – T. Quijano-Medina, Wageningen Univ., Droevendaalsesteeg 2, NL-6708 PB Wageningen, the Netherlands. – A. Gonz a lez-Moreno, Inst. Tecnol o gico de Conkal, Km. 16.3 Antigua Carretera M e rida-Motul, MX-97345 Conkal, Yucat a n, M e xico. Although the eff ects of plant diversity on herbivores are contingent upon herbivore traits and the source of plant diversity (e.g. intra- and interspecifi c), most studies have analyzed these eff ects separately. We compared the eff ects of genotypic diversity of big-leaf mahogany Swietenia macrophylla with that of tree species diversity on two specialist caterpillars (Hypsipyla grandella stem borers and Phyllocnistis meliacella leaf miners) and three generalist leafhoppers (Cicadellidae) feeding on mahogany in a large-scale (7.2 ha) forest diversity experiment in southern Mexico. Th e experiment consisted of fi fty-nine 21 ! 21-m plots, with 64 tree saplings each (3-m spacing between plants). Plots were either mahogany monocul- tures or species polycultures of four species (including mahogany) and – within each of these two plot types – mahogany was represented by either one or four genotypes. Th roughout a fi ve-month period, beginning six months after planting, we measured mahogany growth and monitored herbivore and predator (spider) abundance. We found no eff ect of mahogany genotypic diversity on either specialist caterpillars or generalist leafhoppers, and this result was consistent across levels of tree species diversity. In contrast, species diversity had signifi cant eff ects on both specialists but neither of the generalist herbivores. Specifi cally, species diversity lowered H. grandella attack at the middle of the sampling season, but increased attack at the end of the season, whereas P. meliacella abundance was consistently reduced. Such eff ects were not mediated by eff ects of species diversity on plant growth (of which there were none), but rather through resource heterogeneity. Diversity did not infl uence spider abundance. Th is study is one of few to directly compare sources of plant diversity, and uniquely compares such eff ects among herbivores with contrasting life histories (e.g. diet breadths). Overall, we demonstrate that plant species diversity eff ects outweigh those of genotypes, and our results suggest that such eff ects are stronger on specialist than generalist herbivores. Evidence has mounted for the eff ects of intra- (reviewed by Bailey et al. 2009) and inter-specifi c (Siemann 1998, Haddad et al. 2009) plant diversity on higher trophic levels. Numerous studies have found eff ects of plant diversity on arthropod species richness and abundance (Koricheva et al. 2000, Crutsinger et al. 2006, Haddad et al. 2009) and on consumptive interactions at higher trophic levels (Moreira and Mooney 2013, Abdala-Roberts and Mooney 2014), with the basis of such eff ects being variation in ecologically important traits among plant species or genotypes within species (Hare 2002, Mooney and Singer 2012). Within this context, a widely documented pattern is that greater plant diversity frequently leads to reductions in herbivory (reviewed by Andow 1991, Barbosa et al. 2009). Two hypotheses have been off ered to explain this phenomenon and invoke the infl u- ence of resource heterogeneity on consumers. According to the ‘ enemies hypothesis ’ (hereafter EH; Root 1973), greater habitat complexity at high plant diversity favors increased predator recruitment (e.g. because of greater availability of shelters or prey) resulting in stronger top – down suppression of herbivore populations and thus lower herbivory (reviewed by Russell 1989). Alternatively, the ‘ resource concentra- tion hypothesis ’ (RCH) (Root 1973) holds that herbivore foraging is density-dependent and increasing plant species diversity at a constant plant density reduces the probabil- ity of fi nding a preferred host plant, which lowers herbivore recruitment and damage on individual plants. While both hypotheses have received considerable attention, evi- dence from natural systems has generated mixed support (Bommarco and Banks 2003, Underwood et al. 2014). Th e inconsistent support for the EH and RCH could be due to unaccounted variation in herbivores traits (Vehvil a inen et al. 2007, Plath et al. 2012). For example, the dynamics predicted by the EH should be more likely to occur for generalist herbivores because they are more sus- ceptible to natural enemies as they frequently lack defense mechanisms found in specialists (e.g. crypsis, sequestration of plant toxic compounds; Mooney et al. 2012, Singer et al. EV-1

Although it is known that floral dimorphism contributes to the maintenance of mixed breeding systems, the consequences of producing progeny of a contrasting genetic background and seeds with differential resource allocation has been practically ignored regarding establishment of belowground organisms-plant interactions. This article evaluates the combined effect of floral dimorphism with cross type and light environment on interactions between Ruellia nudiflora and arbuscular mycorrhizal fungi (AMF). R. nudiflora produces cleistogamous (CL) flowers that exhibit obligate self-pollination and chasmogamous (CH) flowers with facultative self- (CHs) or cross- (CHc) pollination. We evaluated the establishment of the plant-AMF interaction in progeny derived from each floral type, under two light conditions (shaded versus open). We established different scenarios depending on the existence of inbreeding depression (ID) and whether the differential resource allocation (DRA) to CH and CL flowers affected the R. nudiflora-AMF interaction. We predicted that under shaded light conditions there might be an intensification of ID, having a negative effect on AMF colonisation. The percentages of hyphae and vesicles in the harvested roots was significantly higher in the shaded plants (F ≥ 4.11, P < 0.05), while progeny of CHc and CHs presented a higher percentage of hyphae and vesicle colonisation compared to CL progeny (F = 15.26, P < 0.01). The results show that DRA to CH flowers and light availability both determines the establishment of R. nudiflora-AMF interaction. The results also suggest that even under stressful light conditions, endogamy does not affect this interaction, which may explain the success of R. nudiflora as an invasive species.

Dimorphic cleistogamy is a specialized form of mixed mating system where a single plant produces both open, potentially outcrossed chasmogamous (CH) and closed, obligately self-pollinated cleistogamous (CL) flowers. Typically, CH flowers and seeds are bigger and energetically more costly than those of CL. Although the effects of inbreeding and floral dimorphism are critical to understanding the evolution and maintenance of cleistogamy, these effects have been repeatedly confounded. In an attempt to separate these effects, we compared the performance of progeny derived from the two floral morphs while controlling for the source of pollen. That is, flower type and pollen source effects were assessed by comparing the performance of progeny derived from selfed CH vs. CL and outcrossed CH vs. selfed CH flowers, respectively. The experiment was carried out with the herb Ruellia nudiflora under two contrasting light environments. Outcrossed progeny generally performed better than selfed progeny. However, inbreeding depression ranges from low (1%) to moderate (36%), with the greatest value detected under shaded conditions when cumulative fitness was used. Although flower type generally had less of an effect on progeny performance than pollen source did, the progeny derived from selfed CH flowers largely outperformed the progeny from CL flowers, but only under shaded conditions and when cumulative fitness was taken into account. On the other hand, the source of pollen and flower type influenced seed predation, with selfed CH progeny the most heavily attacked by predators. Therefore, the effects of pollen source and flower type are environment-dependant and seed predators may increase the genetic differences between progeny derived from CH and CL flowers. Inbreeding depression alone cannot account for the maintenance of a mixed mating system in R. nudiflora and other unidentified mechanisms must thus be involved.

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.