Amandine Bourg

Although it is well-established that soil nutrients determine leaf morpho-physiology and tree dimensions, linking soil physicochemical properties with functional community patterns under field conditions remains difficult. We examine how soil properties shape community-weighted mean (CWM) traits and species composition in pine, mixed, and broadleaf forests along a topographic gradient in the subtropical mountains of western Mexico. We related pH, organic matter, calcium, boron, and silt with stomatal density, stomatal conductance, leaf water potential (Ψ), specific leaf area (SLA), diameter at breast height (DBH), and tree height across three forest types and nine 1000 m ² plots along the gradient. Pine forests, with distinct species composition, occupied stressful environments characterized by acidic soils and low organic matter. They adopted a conservative resources use strategy, with lower CWM-SLA and higher CWM-DBH, along with less negative CWM-Ψ, indicating reduced water stress compared to broadleaf and mixed forests. In contrast, broadleaf and mixed forests inhabit soils without nutrient limitations, showed a more acquisitive strategy, and high species turnover resulted in similar CWM values between them. This functional heterogeneity may be a key factor in the resilience of subtropical forest to disturbances.

β-diversity has been under continuous debate, with a current need to better understand the way in which a new wave of measures work. We assessed the results of 12 incidence-based β-diversity indices. Our results of gradual species composition overlap between paired assemblages considering progressive differences in species richness show the following: (i) four indices (β_-2, β_-3, β_-3.s, and β_r) should be used cautiously given that results with no shared species retrieve results that could be misinterpreted; (ii) all measures conceived specifically as partitioned components of species compositional dissimilarities ought to be used as such and not as independent measures per se; (iii) the non-linear response of some indices to gradual species composition overlap should be interpreted carefully, and further analysis using their results as dependent variables should be performed cautiously; and (iv) two metrics (β_sim and β_sor) behave predictably and linearly to gradual species composition overlap. We encourage ecologists using measures of β-diversity to fully understand their mathematical nature and type of results under the scenario to be used in order to avoid inappropriate and misleading inferences.

Both the impact of habitat modification on the food preferences of species and its impact on ecosystem functioning are poorly understood. In this study, we analyzed food selection by dung beetles in 80 tropical forest fragments and their adjacent cattle pastures in the Los Tuxtlas Biosphere Reserve, Mexico. Ten pitfall traps were placed at each site, half baited with human dung and the other half with fish carrion. We assessed dung beetle food selection and classified any specialization in resource use quantitatively using a multinomial classification model. We collected 15,445 beetles belonging to 42 species, 8747 beetles (38 species) in forest fragments and 6698 beetles (29 species) in cattle pastures. Twenty-five species were present in both habitats. Of all the beetles captured, 76% were caught in dung traps (11,727 individuals) and 24% in carrion traps (3718 individuals). We found 21 species of dung specialists, 7 carrion specialists, 8 generalists, and 6 species too rare to classify. The bait most frequently selected by beetles in this study was dung in both forests and pastures. Specialists tended to remain specialists in both habitats, while generalists tended to change their selection of bait type depending on the habitat. In summary, our results show that replacing forests with cattle pastures modifies the patterns of resource selection by dung beetles and this could affect ecosystem functioning.