Artículo de publicación ISIA high proportion of plant species is predicted to be threatened with extinction in the near future. However, the threat status of only a small number has been evaluated compared with key animal groups, rendering the magnitude and nature of the risks plants face unclear. Here we report the results of a global species assessment for the largest plant taxon evaluated to date under the International Union for Conservation of Nature (IUCN) Red List Categories and Criteria, the iconic Cactaceae (cacti). We show that cacti are among the most threatened taxonomic groups assessed to date, with 31% of the 1,478 evaluated species threatened, demonstrating the high anthropogenic pressures on biodiversity in arid lands. The distribution of threatened species and the predominant threatening processes and drivers are different to those described for other taxa. The most significant threat processes comprise land conversion to agriculture and aquaculture, collection as biological resources, and residential and commercial development. The dominant drivers of extinction risk are the unscrupulous collection of live plants and seeds for horticultural trade and private ornamental collections, smallholder livestock ranching and smallholder annual agriculture. Our findings demonstrate that global species assessments are readily achievable for major groups of plants with relatively moderate resources, and highlight different conservation priorities and actions to those derived from species assessments of key animal groupsConsejo Nacional de Ciencia y Tecnologia 000000000011820

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Summary1. There is an ongoing debate about whether communities are closely integrated and bound together via interactions such as competition or facilitation, or are disintegrated and dominated by chance. We still lack community-wide data on the intensities of interactions and randomness, and measurements of their impacts on community structure. 2. Using a long-term data set, we sought to measure the effects of interactions and stochasticity in structuring a highly diverse (>100 species) semi-arid grassland plant community, testing for positive and negative interactions at different stages of population growth of all species. 3. During the colonization of new patches, most species were facilitated or inhibited by several others. These opposite effects can potentially have a large effect on species abundances, but they were correlated and cancelled out at the community level. Nevertheless, competition during colonization was strong enough to cause poor competitors to have small population sizes. 4. The subsequent phase of population growth (increase and subsequent change in numbers within occupied patches) was mainly driven by intraspecific density dependence, and we found little evidence for interspecific interactions. 5. Model results showed that stochasticity and recurrent colonization of transient, favourable patches maintained diversity, keeping poor competitors from becoming extinct. 6. Synthesis: Our results, taken together with recent studies on tropical forests, suggest that weak interactions among established plants may be a general phenomenon, but that local interactions during colonization are important drivers of community composition. Most of the variance in species abundance in our community was explained by intraspecific competition and stochasticity, with interspecific interactions playing a minor role due to their overall weakness, interaction changes over ontogeny, and the cancellation of opposite-sign interactions when all the species in the community are considered. Despite this, some species were rare seemingly because they cannot withstand interspecific competition. Thus, to untangle the effects of interactions on community structure, future research should focus on interactions occurring at different phases of population growth and on whole communities.

Ecological restoration has become an important technique for mitigating the human impacts on natural vegetation. Planting seedlings is the most common approach to regain lost forest cover. However, these activities require a large economic investment. Direct seeding is considered a cheaper and easier alternative technique, in which tree seeds are introduced directly on the site rather than transplanting seedlings from nurseries. To evaluate the effectiveness of direct seeding, we conducted a comprehensive search of the literature using 'restoration', 'direct seeding' and 'sowing' as keywords, and we performed a meta-analysis using 30 papers and 89 species. We used two different measures of restoration success: seed germination probability and success probability (the chance that a seed germinates and survives until the end of the experiment). In general, restoration attempts using direct-seeding techniques were relatively unsuccessful. On average, seed germination and success probability were 0·239 and 0·114, respectively, and were not affected by climate, species successional group or the application of pre-germinative treatments. Germination and success probability increased with seed size, and the use of physical protections resulted in a nearly twofold increase in germination probability, but this effect faded by the end of the experiments. Because of the low rate of seedling success, we suggest the use of direct seeding as a complementary technique to reduce restoration costs, particularly for species with large seeds and known high germination rates, but our results do not support direct seeding as a substitute for seedling planting.

Plants that use fog as an important water-source frequently have a rosette growth habit. The performance of this morphology in relation to fog interception has not been studied. Some first-principles from physics predict that narrow leaves, together with other ancillary traits (large number and high flexibility of leaves, caudices, and/or epiphytism) which constitute the "narrow-leaf syndrome" should increase fog-interception efficiency. This was tested using aluminum models of rosettes that differed in leaf length, width and number and were exposed to artificial fog. The results were validated using seven species of Tillandsia and four species of xerophytic rosettes. The total amount of fog intercepted in rosette plants increased with total leaf area, while narrow leaves maximized interception efficiency (measured as interception per unit area). The number of leaves in the rosettes is physically constrained because wide-leafed plants can only have a few blades. At the limits of this constraint, net fog interception was independent of leaf form, but interception efficiency was maximized by large numbers of narrow leaves. Atmospheric Tillandsia species show the narrow-leaf syndrome. Their fog interception efficiencies were correlated to the ones predicted from aluminum-model data. In the larger xerophytic rosette species, the interception efficiency was greatest in plants showing the narrow-leaf syndrome. The adaptation to fog-harvesting in several narrow-leaved rosettes was tested for evolutionary convergence in 30 xerophytic rosette species using a comparative method. There was a significant evolutionary tendency towards the development of the narrow-leaf syndrome the closer the species grew to areas where fog is frequently available. This study establishes convergence in a very wide group of plants encompassing genera as contrasting as Tillandsia and Agave as a result of their dependence on fog.

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Citation: Zepeda, V., and C. Martorell. 2019. Fluctuation-independent niche differentiation and relative non-linearity drive coexistence in a species-rich grassland. Ecology 100(8):Abstract. Despite the advances in ecological theory, evidence for the relative importance of the different mechanisms that promote species coexistence is lacking. Some mechanisms depend on the presence of interannual fluctuations in the environment combined with interspecific differences in the responses to such fluctuations. Among coexistence mechanisms, niche differentiation and storage effects have received much attention, whereas relative nonlinearity (RNL) has been thought to be an unlikely and weak mechanism for multi-species coexistence and remains untested in nature. We quantified the relative contribution of different mechanisms to the coexistence of 19 grassland species by using field-parameterized population models and invasion analysis. Our results showed that 17 out of 19 species had the potential to coexist stably. Species diversity was maintained by RNL and large fluctuation-independent niche differences, i.e., between-species differentiation that is unrelated to interannual variations in environmental factors. Moreover, RNL increased the fitness of species that were less favored by niche differentiation, contributing to their persistence in the community. Storage effect was negligible or destabilizing, making no contribution to stable coexistence. These results, altogether with recent theoretical developments and indirect evidence in published data, call for a reassessment of RNL as a relevant mechanism for multi-species coexistence in nature.

Biodiversity conservation and ecosystem-service provision will increasingly depend on the existence of secondary vegetation. Our success in achieving these goals will be determined by our ability to accurately estimate the structure and diversity of such communities at broad geographic scales. We examined whether the texture (the spatial variation of the image elements) of very high-resolution satellite imagery can be used for this purpose. In 14 fallows of different ages and one mature forest stand in a seasonally dry tropical forest landscape, we estimated basal area, canopy cover, stem density, species richness, Shannon index, Simpson index, and canopy height. The first six attributes were also estimated for a subset comprising the tallest plants. We calculated 40 texture variables based on the red and the near infrared bands, and EVI and NDVI, and selected the best-fit linear models describing each vegetation attribute based on them. Basal area (R 2 = 0.93), vegetation height and cover (0.89), species richness (0.87), and stand age (0.85) were the best-described attributes by two-variable models. Cross validation showed that these models had a high predictive power, and most estimated vegetation attributes were highly accurate. The success of this simple method (a single image was used and the models were linear and included very few variables) rests on the principle that image texture reflects the internal heterogeneity of successional vegetation at the proper scale. The vegetation attributes best predicted by texture are relevant in the face of two of the gravest threats to biosphere integrity: climate change and biodiversity loss. By providing reliable basal area and fallow-age estimates, image-texture analysis allows for the assessment of carbon sequestration and diversity loss rates. New and exciting research avenues open by simplifying the analysis of the extent and complexity of successional vegetation through the spatial variation of its spectral information.