Oak species (Fagaceae: Quercus) differ in their distribution at the landscape scale, specializing to a certain portion of environmental gradients. This suggests that functional differentiation favors habitat partitioning among closely related species. To elucidate the mechanisms of species coexistence in oak forests, we explored patterns of interspecific variation in functional traits involved in water-use strategies. We tested the hypothesis that oak species segregate along key trade-offs between xylem hydraulic efficiency and safety, and between hydraulic safety and drought avoidance capacity, leading to species niche partitioning across a gradient of aridity. To do so, we quantified biophysical and physiological traits in four red and five white oak species (sections Lobatae and Quercus, respectively) across an aridity gradient in central Mexico. We also explored the trade-offs guiding species differentiation, particularly between the drought tolerance versus water acquisition capacity, and determined whether the water-use strategy was associated with the portion of the environmental gradient that the species occupy. In a trait-by-trait analysis, we detected differences between white and red oak species. However, a larger part of the variation was explained at the species rather than at the section level. We detected two primary axes of trait covariation. The first exhibited differences between species with dense tissues and species with soft tissues (the tissue construction cost axis); however, the oak sections did not constitute separate groups, while the second suggested a trade-off between xylem resistance to cavitation and tree deciduousness. As expected, the water-use strategies of the species were related to the environment; oak species from arid areas had more deciduousness and a higher instantaneous water-use efficiency. In contrast, their humid counterparts had less deciduousness and had a xylem that was more resistant to embolisms. Altogether, these results suggest that aridity filters closely related species, resulting in habitat partitioning and niche divergence.

Elucidating the factors determining plant distribution is still on discussion. It has been stated that the distribution is mostly determined by environmental factors, but the evidence on whether this or other processes are the determinants remains inconclusive. In the present study, we hypothesized that oak species differ in their distribution, which might be mostly influence by the environment. Particularly, we explored: i) the patterns of distribution of Quercus species at a landscape scale; ii) the climatic, soil and topographic factors that might determine their distribution, and iii) the degree of association between the species within fragments. The study included the analysis of 78 oak forest fragments at the Cuitzeo lake Basin in Michoacán state, Mexico in which nine oak species were registered. The species showed clear differences in their distribution; three groups of oak species that differ significantly in their spatial arrangement were detected with a NMDS (Non-metric Multidimensional Scaling) analysis. We observed a relationship between oak species distribution with temperature and precipitation. In particular, Q. candicans, Q. crassipes and Q. rugosa were frequently distributed at sites with higher rainfall and lower temperature; in contrast, Q. deserticola, Q. gentryi and Q. glaucoides were at more arid areas. We found associations between pairs of oak species; the most recurrent one was between species from the Quercus and the Lobatae sections. Overall, the pattern of distribution among oak species was determined by environmental factors, which suggests that they partition their habitat to avoid competition for resources. Key words: coexistence, ecological niche, habitat fragmentation, patterns of distribution, oaks. Patrones de distribución de nueve especies de Quercus a lo largo de un gradiente ambiental en un paisaje fragmentado del centro de México ResumenElucidar los factores que determinan la distribución de las plantas todavía se encuentra en debate. Se ha dicho que la distribución es principalmente determinada por factores ambientales, pero la evidencia de si estos u otros procesos son los más determinantes aún no es concluyente. En el presente estudio, se predijo que las especies de Quercus difieren en su distribución, y está principalmente determinada por el ambiente. En particular, se exploró: i) los patrones de distribución de especies de Quercus en una escala de paisaje; ii) si los factores climáticos, edáficos y topográficos determinan su distribución; y iii) el grado de asociación entre especies dentro de los fragmentos. En este estudio se censaron 78 fragmentos de encinares en la Cuenca de Cuitzeo en el estado de Michoacán, México, en los cuales se registraron nueve especies de encinos. Las especies mostraron claras diferencias en su distribución; tres grupos de especies de Quercus que difieren significativamente en su arreglo espacial fueron detectados con un análisis NMDS (Escalamiento Multidimensional No-métrico). Así mismo, se observó una relación entre la distribució...

Many parasitic wasps use volatiles emitted by plants under herbivore attack to find their hosts. It has therefore been proposed that these inducible plant volatiles serve an indirect defense function by recruiting parasitoids and other natural enemies. This suggested function remains controversial because there is little evidence that, in terms of fitness, plants benefit from the actions of natural enemies, particularly parasitoids, which do not immediately kill their hosts. We aimed to address this controversy in a semi-natural field experiment in Mexico, where we used large screen tents to evaluate how parasitoids can affect plant performance. The tritrophic study system comprised teosinte (Zea spp.), the ancestor of maize, Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) and Campoletis sonorensis Cameron (Hymenoptera: Ichneumonidae), which have a long evolutionary history together. In tents without parasitoids, S. frugiperda larvae inflicted severe damage to the plants, whereas in the presence of parasitoid wasps, leaf damage was reduced by as much as 80%. Parasitoids also mitigated herbivore-mediated mortality among young teosinte plants. Although these findings will not resolve the long-standing debate on the adaptive function of herbivore-induced plant volatiles (HIPVs), they do present strong support for the hypothesis that plants can benefit from the presence of parasitoid natural enemies of their herbivores.

Litter fungal communities and their ligninolytic enzyme activities (laccase, Mn-peroxidase, and lignin-peroxidase) play a vital role in forest biogeochemical cycles by breaking down plant cell wall polymers, including recalcitrant lignin. However, litter fungal communities and ligninolytic enzyme activities have rarely been studied in Neotropical, non-coniferous forests. Here, we found no significant differences in litter ligninolytic enzyme activities from well preserved, moderately disturbed, and heavily disturbed Quercus deserticola Trel. forests in central Mexico. However, we did find seasonal effects on enzyme activities: during the dry season, we observed lower laccase, and increased Mn-peroxidase and lignin-peroxidase activities, and in the rainy season, Mn-peroxidase and lignin-peroxidase activities were lower, while laccase activity peaked. Fungal diversity (Shannon-Weaver and Simpson indices) based on ITS-rDNA analyses decreased with increased disturbance, and principal component analysis showed that litter fungal communities are structured differently between forest types. White-rot Polyporales and Auriculariales only occurred in the well preserved forest, and a high number of Ascomycota were shared between forests. While the degree of forest disturbance significantly affected the litter fungal community structure, the ligninolytic enzyme activities remained unaffected, suggesting functional redundancy and a possible role of generalist Ascomycota taxa in litter delignification. Forest conservation and restoration strategies must account for leaf litter and its associated fungal community.