Oaks are a dominant woody plant genus in the northern hemisphere that occupy a wide range of habitats and are ecologically diverse. We implemented a functional trait approach that included nine functional traits related to leaves and stems in order to explain the species coexistence of 21 oak species along a water availability gradient in a temperate forest in Mexico. This particular forest is characterized as a biodiversity hotspot, with many oak species including some endemics. Our main aim was to investigate whether the different oak species had specific trait associations that allow them to coexist along an environmental gradient at regional scale. First, we explored trait covariation and determined the main functional dimensions in which oaks were segregated. Second, we explored how environmental variation has selected for restricted functional dimensions that shape oak distributions along the gradient, regardless of their leaf life span or phylogeny (section level). Third, we quantified the niche overlap between the oak functional spaces at different levels. The analyzed species showed three functional dimensions of trait variation: a primary axis related to the leaf economic spectrum, which corresponds to the segregation of the species according to leaf habit; a second axis that reflects the stem hydraulic properties and corresponds to species segregation followed by phylogenetic segregation, reflecting some degree of trait conservatism, and a third axis, represented mainly by leaf area and plant height, that corresponds to species segregation. Finally, our findings indicated that the functional space measured with leaf traits and stem traits such as hydraulic capacity was integrally linked to niche differentiation. This linkage suggests that the earliest mechanism of species segregation was related to habitat suitability and that the stem hydraulic trade-off reflects differences between phylogenetic sections; these traits may promote coexistence between distantly related oak species.

Background: Analyzing interactions between vegetation and environmental factors at regional scales provide information for the understanding of species assemblages. Hypotheses: Environmental restrictions at higher elevations produce a decreasing species richness pattern along an elevational gradient and the climatic variables related to temperature and precipitation are the main filters of species distribution. Objectives: (1) To identify the different assemblages of tree species occurring in a biodiversity hotspot; (2) to analyze the pattern of tree species richness along an elevational gradient; and (3) to analyze the environmental filters that determine the species distribution. Study site: Serranías Meridionales of Jalisco in western Mexico. Period of study: 2016-2018. Methods: Thirty-three rectangular 0.1 ha plots were established for vegetation and environmental characterization. Cluster and canonical correspondence analyses were conducted to analyze tree species composition. We defined three groups of variables (climatic, relief and soil) to evaluate the influence of environmental filters. We used generalized linear models to assess the contribution of each group to the spatial variation in species richness. Results: A total of 63 tree species were recorded. The cluster analysis defined eight groups within three forest types. The species richness showed a hump-shaped pattern along the elevational gradient and the climatic and soil variables explained a considerable amount of variation in the species richness. Conclusions: The tree species richness in the Serranías Meridionales de Jalisco is dominated by a striking number of Pinus and Quercus species. This biodiversity hotspot is an important site for the understanding of tree ecological diversification in Mexico.

BackgroundMany species of birds are morphologically and physiologically adapted for migration. Migratory movements of birds can range from thousands of kilometers, such as when birds migrate from wintering to breeding sites in summer, to several kilometers, such as when birds migrate among habitats in a single mountain system. The main factor that influences bird migration is the seasonal fluctuation of food resources; climate, predation, competition for resources and endogenous programming are also important factors. Hummingbirds are highly dependent on nectar, so their migration is likely correlated with the blooming of plant species. The ecological implications of altitudinal migration in the mountains of North America as well as the latitudinal migration of Selasphorus rufus through Mexico are still poorly understood. To explore these issues, over three non-consecutive years, we evaluated interannual variation in the phenologies of a latitudinal migrant (S. rufus) and an altitudinal migrant (Amazilia beryllina) and their visited plants.MethodsWe assessed the relationship between two migratory hummingbirds and flower abundance in 20 fixed-radius plots (25 m radius). All available flowers were counted along transects (40 × 5 m) inside each fixed-radius plot. Sampling was performed every 10 days from November 12 through February 20 of 2010–2011, 2013–2014 and 2015–2016, resulting in a total of 11 samples of each plot per period. Phenological variation and the relationships among hummingbird abundance, flower abundance and vegetation type were evaluated using a generalized additive mixed model.ResultsS. rufus abundance was related to sampling time in the first and third periods; this relationship was not significant in the second period. A. beryllina abundance was related with the sampling time over all three periods. The abundance of S. rufus hummingbirds was significantly related to the number of Salvia iodantha flowers. The abundance of A. beryllina hummingbirds was related to the number of S. iodantha and Cestrum thyrsoideum flowers and the total number of flowers. We found a non-significant correlation between S. rufus and A. beryllina abundance and vegetation types.ConclusionContrary to expectations, the long-distance migration of S. rufus was not consistent over the sampling periods. The migration of S. rufus through the study region may be altered by changes in climate, as has occurred with other species of migratory birds. In the present study, the migration of S. rufus was correlated with the blooming of S. iodantha. In comparison, the altitudinal migrant A. beryllina responded to the availability of floral resources but was not associated with a particular plant. The migration of this latter species in the area probably depends on multiple factors, including climatic and demographic factors, but is particularly dependent on the supply of floral resources and competition for these resources.

Autores. Editado por la AEET. [Ecosistemas no se hace responsable del uso indebido de material sujeto a derecho de autor]

Oaks (Quercus L.) are a dominant woody plant genus in the northern hemisphere, which occupy a wide range of habitats and are ecologically diverse. We analyzed the wood anatomical traits, the variables derived, and the relative hydraulic conductivity of 21 oak species to identify their performance according to abiotic factors, leaf phenological patterns, and phylogenetic restrictions by analyzing the interspecific variation along an environmental gradient. First, we determine the causes of anatomical trait variation in the oaks, analyzing the functional trade-offs related to distribution along the environmental gradient. We measure the phenotypic plasticity of the anatomical traits to determine the role of environment and geographic distance in the range of phenotypic plasticity. Second, we examined if oaks co-occurred along the environmental gradient. Then we analyzed if wood anatomical traits reflect differences among their phylogenetic section, leaf habit, and a phylogenetic section/leaf habit category. Last, we tested the phylogenetic signal. Our results showed that vessel diameter, vessel frequency, wood density, and relative hydraulic conductivity are the main axes of trait variation in the species analyzed among leaf habit categories. The aridity index and seasonal precipitation drive the variation in the analyzed traits. Higher environmental distance resulted in a higher relative distance plasticity index among traits. Co-occurrence of oak species with different leaf habits and phylogenetic trajectories may promote complementary resource acquisition. The phylogenetic signal in the oak species studied was low, which implies labile wood traits.