ABSTRACT
The mechanisms of drought resistance that allow plants to successfully establish at different stages of secondary succession in tropical dry forests are not well understood. We characterized ...mechanisms of drought resistance in early and late‐successional species and tested whether risk of drought differs across sites at different successional stages, and whether early and late‐successional species differ in resistance to experimentally imposed soil drought. The microenvironment in early successional sites was warmer and drier than in mature forest. Nevertheless, successional groups did not differ in resistance to soil drought. Late‐successional species resisted drought through two independent mechanisms: high resistance of xylem to embolism, or reliance on high stem water storage capacity. High sapwood water reserves delayed the effects of soil drying by transiently decoupling plant and soil water status. Resistance to soil drought resulted from the interplay between variations in xylem vulnerability to embolism, reliance on sapwood water reserves and leaf area reduction, leading to a tradeoff of avoidance against tolerance of soil drought, along which successional groups were not differentiated. Overall, our data suggest that ranking species' performance under soil drought based solely on xylem resistance to embolism may be misleading, especially for species with high sapwood water storage capacity.
In this study we characterized patterns of variation in the resistance to soil drought among tropical dry forest tree seedlings, and tested whether risk of drought differs across sites of different successional stages and whether early and late‐successional species differ in resistance to experimentally imposed soil drought. Although early successional sites were warmer and drier than mature forest, early and late‐successional species did not differ in their resistance to soil drought, indicating multiple strategies within each group for coping with drought. We detected broad variation in resistance to soil drought among species and a trade‐off between xylem resistance to embolism and leaf loss, apparently mediated by variation in sapwood water storage capacity; high sapwood water storage capacity seemed to uncouple seedling water status from that of the soil during several weeks of soil drying. Overall, resistance to soil drought of a given species resulted from the interplay between variation in xylem vulnerability to embolism, reliance on sapwood water reserves and leaf area reduction.
ABSTRACT
A common observation in tropical dry forests is the habitat preference of tree species along spatial soil water gradients. This pattern of habitat partitioning might be a result of species ...differentiation in their strategy for using water, along with competing functions such as maximizing water exploitation and tolerating soil water stress. We tested whether species from drier soil conditions exhibited a tolerance strategy compared with that of wet‐habitat species. In a comparison of 12 morphophysiological traits in seedlings of 10 closely related dry and wet‐habitat species pairs, we explored what trade‐offs guide differentiation between habitats and species. Contrary to our expectations, dry‐habitat species showed mostly traits associated with an exploitation strategy (higher carbon assimilation capacity, specific leaf area and leaf‐specific conductivity and lower water‐use efficiency). Strikingly, dry‐habitat species tended to retain their leaves longer during drought. Additionally, we detected multiple strategies to live within each habitat, in part due to variation of strategies among lineages, as well as functional differentiation along the water storage capacity–stem density (xylem safety) trade‐off. Our results suggest that fundamental trade‐offs guide functional niche differentiation among tree species expressed both within and between soil water habitats in a tropical dry forest.
In the tropical dry forest, water availability is highly heterogeneous in space, given topographic variation at the local scale, however, whether plant species are functionally differentiated along water gradients remains poorly studied. We tested whether dry‐habitat specialists exhibit a conservative strategy to use resources, compared to species inhabiting the wet habitat. Contrary to our expectation, dry habitat species showed mostly traits associated with an exploitation strategy, suggesting a strong ecological pressure for accelerating growth in the dry habitats due to a shortened growth‐time window. Additionally, we detected multiple strategies to live within each habitat, mostly due to functional differentiation along the water storage capacity‐stem density (xylem safety) trade‐off. This study contributes to the understanding of the diversity of seedlings functional strategies in the tropical dry forest, by exhibiting the covariation of multiple traits and the differentiation between soil‐water habitats along fundamental trade‐offs.
Background
Digital clubbing is a well‐known clinical sign characterized by thickening of the distal phalanges of the fingers and toes. Unilateral clubbing occurs less frequently. A previous report ...showed for the first time two cases of unilateral clubbing as a clinical manifestation of lower limb venous malformation. The objective of the present study is to describe a series of 13 patients with a low‐flow vascular malformation where a clubbing‐like unilateral digital thickening is also observed.
Methods
All patients were retrospectively included after reviewing clinical photographs from a vascular malformations database.
Results
A total of 13 patients with low‐flow vascular malformations were included in this study. The mean age at diagnosis was 11 years (range 5–26 years) with a female predominance (nine patients). The most frequent vascular malformation collected was a blue rubber bleb nevus syndrome in four patients, followed by common venous malformations in three patients. All patients characteristically exhibited a clubbing‐like digital thickening. Seven patients had foot involvement and six patients hand involvement.
Conclusions
Although the number of cases is limited, our study is the first series of cases where a clubbing‐like digital thickening is described in patients with a low‐flow vascular malformation. The unilateral presence of clubbing or pseudoclubbing should lead to the suspicion of an underlying vascular malformation.
Connectivity is a landscape property that promotes gene flow between organisms located in different patches of habitat and provides a way to reduce habitat loss by maintaining flux of organisms ...through the landscape; it is an important factor for conservation decisions. In this study, we evaluated the structural and functional connectivity among 510 oak forest remnants in a basin in central Mexico by modeling the potential distribution of seven oak species that inhabit in it. The structural and functional connectivity of oak forest remnants was estimated by graph theory. Distribution models for all the oak species had a good level of predictability, showing that 53.16% of the basin is suitable for oaks. The importance for connectivity varied between the remnant forests. Large forest fragments had the highest values of connectivity, and small forest fragments acted as steppingstones favoring the movement of organisms among fragments. In the southern region of the basin, connected remnant forests had conformed to a large network, but in the northern region, the remnant forests were mostly isolated. Conservation of oak forests in this basin requires protection for remaining patches by preserving both large and small ones and restoring biological corridors to reduce the isolation of forest fragments.
The study of above- and below-ground organ plant coordination is crucial for understanding the biophysical constraints and trade-offs involved in species' performance under different environmental ...conditions. Environmental stress is expected to increase constraints on species trait combinations, resulting in stronger coordination among the organs involved in the acquisition and processing of the most limiting resource. To test this hypothesis, we compared the coordination of trait combinations in 94 tree seedling species from two tropical forest systems in Mexico: dry and moist. In general, we expected that the water limitation experienced by dry forest species would result in stronger leaf-stem-root coordination than light limitation experienced by moist forest species. Using multiple correlations analyses and tools derived from network theory, we found similar functional trait coordination between forests. However, the most important traits differed between the forest types. While in the dry forest the most central traits were all related to water storage (leaf and stem water content and root thickness), in the moist forest they were related to the capacity to store water in leaves (leaf water content), root efficiency to capture resources (specific root length), and stem toughness (wood density). Our findings indicate that there is a shift in the relative importance of mechanisms to face the most limiting resource in contrasting tropical forests.
1. Successional gradients are ubiquitous in nature, yet few studies have systematically examined the evolutionary origins of taxa that specialize at different successional stages. Here we quantify ...successional habitat specialization in Neotropical forest trees and evaluate its evolutionary lability along a precipitation gradient. Theoretically, successional habitat specialization should be more evolutionarily conserved in wet forests than in dry forests due to more extreme microenvironmental differentiation between early and late-successional stages in wet forest. 2. We applied a robust multinomial classification model to samples of primary and secondary forest trees from 14 Neotropical lowland forest sites spanning a precipitation gradient from 788 to 4000 mm annual rainfall, identifying species that are old-growth specialists and secondary forest specialists in each site. We constructed phylogenies for the classified taxa at each site and for the entire set of classified taxa and tested whether successional habitat specialization is phylogenetically conserved. We further investigated differences in the functional traits of species specializing in secondary vs. old-growth forest along the precipitation gradient, expecting different trait associations with secondary forest specialists in wet vs. dry forests since water availability is more limiting in dry forests and light availability more limiting in wet forests. 3. Successional habitat specialization is non-randomly distributed in the angiosperm phylogeny, with a tendency towards phylogenetic conservatism overall and a trend towards stronger conservatism in wet forests than in dry forests. However, the specialists come from all the major branches of the angiosperm phylogeny, and very few functional traits showed any consistent relationships with successional habitat specialization in either wet or dry forests. 4. Synthesis. The niche conservatism evident in the habitat specialization of Neotropical trees suggests a role for radiation into different successional habitats in the evolution of species-rich genera, though the diversity of functional traits that lead to success in different successional habitats complicates analyses at the community scale. Examining the distribution of particular lineages with respect to successional gradients may provide more insight into the role of successional habitat specialization in the evolution of species-rich taxa.
Introduction: The diagnostic yield (DY) of small-bowel capsule endoscopy (SBCE) varies considerably according to its indication. Some strategies have been used to increase DY with varying results. ...The intention of this study was to identify whether evaluation of the SBCE recordings by a second reviewer can increase DY and change patient management. Methods: One hundred SBCEs with different indications, already read by an endoscopist were read by a second blinded endoscopist. When the results of the 2 readings were different, the images were discussed by the endoscopists; if no consensus was reached, they took the opinion of a third endoscopist into account. All the participating endoscopists had experience in reading SBCEs (i.e., >50 per year). The SBCE findings were divided into positive (vascular lesions, ulcers, and tumors), equivocal (erosions or red spots), and negative. The interobserver agreement and the increase in DY were assessed as well as the percentage of false-negatives (FNs) in the first evaluation. Results: The indications for SBCE were small-bowel bleeding (SBB) in 48 cases, Crohn’s disease (CD) in 30, and other causes (iron-deficiency anemia, small-bowel tumors, and diarrhea) in 22. There was substantial interobserver agreement between evaluations (κ = 0.79). The findings in the first evaluation were positive in 60%, equivocal in 20% and, negative in 20%. In the second evaluation, 66% were positive, 18% were equivocal, and 16% were negative. The increase in DY with the second reading was 6% (p = 0.380), i.e., 6.3% for SBB, 4.4% for CD and 9.2% for other indications, resulting in a change in management of 4% of the patients. FNs in the first SBCE reading were found in 4% of the SBCEs. Discussion: A second evaluation of the SBCE recordings identified significant pathology that the first evaluation had missed, resulting in a nonsignificant 6% increase in DY and a change in the management of 4% of the patients.
Tropical dry forests are environmentally complex ecosystems with highly heterogeneous water availability, such that distinctive plant communities are found in contrasting habitats in close proximity ...to each other. This leads to the question of how resource heterogeneity has led to functional heterogeneity among communities. One hypothesis is that the main trade‐offs and the size of the functional space should diverge between communities that differ in their most limiting resource. To test this, we compared aboveground and belowground traits of saplings of 33 dominant species from the dry forest plant communities of two locations that differ in water and also in light availability. In the drier community, the major functional dimension described a trade‐off between drought tolerance and drought avoidance strategies. This dimension was also evident in the wetter community; however, traits related to the efficiency of resource capture were decoupled from the drought tolerance‐drought avoidance trade‐off. Trees from the wetter community tended to develop more efficient fine roots for resource capture. The functional space of the drier and more heterogenous forest was larger than the wetter forest, and plant strategies to deal with drought accounted for a much larger portion of trait variation. Overall, functional differentiation may occur between systems that are close in proximity but differ in the availability of resources such as water and light. These environmental differences cause plant communities to differ in functional properties both aboveground and belowground, likely promoting heterogeneous responses to anthropogenic and natural disturbances at the landscape scale.
in Spanish is available with online material.
RESUMEN
Los bosques tropicales secos son ecosistemas ambientalmente complejos con alta heterogeneidad en la disponibilidad del agua, de manera que es posible encontrar diferentes comunidades vegetales en hábitats contrastantes muy cercanos entre sí. Esto lleva a la pregunta de cómo la heterogeneidad de recursos conduce a la heterogeneidad funcional entre comunidades. Una hipótesis es que las principales disyuntivas y el tamaño del espacio funcional deberían divergir entre comunidades que difieren en el recurso más limitante. Para probar esta hipótesis comparamos rasgos funcionales por encima y por debajo del suelo en plántulas de 33 especies dominantes del bosque tropical seco, de dos comunidades vegetales que difieren en la disponibilidad del agua y de la luz. En el hábitat más seco la principal dimensión funcional describe una disyuntiva entre las estrategias de tolerancia y evasión de la sequía. Esta dimensión también fue evidente en la comunidad más húmeda, sin embargo, los rasgos relacionados con la eficiencia en la captura de recursos se desacoplaron de la disyuntiva entre tolerar y evadir la sequía. Las especies de la comunidad más húmeda desarrollaron más raíces finas que son más eficientes en la captura de recursos. El espacio funcional del bosque más seco y heterogéneo fue mucho mayor que el del bosque húmedo, y las estrategias de las plantas para enfrentar la sequía representaron una porción mucho mayor de la variación de los rasgos. Estas diferencias ambientales provocan que las comunidades vegetales difieran en sus propiedades funcionales tanto por encima como por debajo del suelo, promoviendo probablemente respuestas heterogéneas a las perturbaciones antropogénicas y naturales a escala del paisaje.
By comparing aboveground and belowground traits of saplings from two distinctive dry forest plant communities differing in water and light availability we found that in the wetter community traits related to the efficiency of resource capture were decoupled from the drought‐tolerance drought‐avoidance trade‐off thus developing more efficient fine roots. Furthermore, functional space of the drier and more heterogeneous forest was much larger than the wetter forest. We discuss how limiting resources may drive functional differentiation between plant communities thriving in contrasting habitats. Photo credit: Leopoldo D. Vázquez Reyes, Biosphera Picture A.C.
In seasonal plant communities where water availability changes dramatically both between and within seasons, understanding the mechanisms that enable plants to exploit water pulses and to survive ...drought periods is crucial. By measuring rates of physiological processes, we examined the trade-off between water exploitation and drought tolerance among seedlings of trees of a tropical dry forest, and identified biophysical traits most closely associated with plant water-use strategies. We also explored whether early and late secondary successional species occupy different portions of trade-off axes. As predicted, species that maintained carbon capture, hydraulic function and leaf area at higher plant water deficits during drought had low photosynthetic rates, xylem hydraulic conductivity and growth rate under non-limiting water supply. Drought tolerance was associated with more dense leaf, stem and root tissues, whereas rapid resource acquisition was associated with greater stem water storage, larger vessel diameter and larger leaf area per mass invested. We offer evidence that the water exploitation versus drought tolerance trade-off drives species differentiation in the ability of tropical dry forest trees to deal with alternating water-drought pulses. However, we detected no evidence of strong functional differentiation between early and late successional species along the proposed trade-off axes, suggesting that the environmental gradient of water availability across secondary successional habitats in the dry tropics does not filter out physiological strategies of water use among species, at least at the seedling stage.
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