Species alliances and hidden niche dimensions drive species clustering along a hydric gradient in a semiarid grassland.

Clustering of species with similar niches or traits occurs in communities, but the mechanisms behind this pattern are still unclear. In the emergent neutrality model, species with similar niches and competitive ability self-organise into clusters. In the hidden-niche model, unaccounted-for niche differences stabilise coexistence within clusters. Finally, clustering may occur through alliances of species that facilitate each other. We tested these hypotheses using population-growth models that consider interspecific interactions parameterised for 35 species using field data. We simulated the expected community dynamics under different species-interaction scenarios. Interspecific competition was weaker within rather than between clusters, suggesting that differences in unmeasured niche axes stabilise coexistence within clusters. Direct facilitation did not drive clustering. In contrast, indirect facilitation seemingly promoted species alliances in clusters whose members suppressed common competitors in other clusters. Such alliances have been overlooked in the literature on clustering, but may arise easily when within cluster competition is weak.

Plant-soil feedbacks depend on drought stress, functional group, and evolutionary relatedness in a semiarid grassland.

Plant-soil feedback (PSF) occurs when plants change the biota and physicochemical properties of the soil, and these changes affect future survival or growth of plants. PSF depends on several factors such as plant functional attributes (e.g., life cycle or photosynthetic metabolism) and the environment. PSF often turn positive under dry conditions because soil biota confers drought tolerance. Conspecifics and close relatives share pathogens and consume similar resources, exerting negative PSF on each other. These ideas have mostly been tested under controlled conditions, while field studies remain scarce. To reevaluate these findings in nature, we analyzed plant-soil feedbacks over a drought-stress gradient in a phosphorus-limited semiarid grassland. We planted seedlings of 17 species in plots where community composition had been monitored for six years. To determine PSF intensity, we measured how seedling longevity was affected by previous occupancy of conspecifics and heterospecifics. The previous occupancy-survival relationship (OSR) was used as a proxy for PSF. Evidence for OSRs was found in one-third of the species pairs, with inconclusive evidence for the rest suggesting weak feedbacks. This is in line with the expectation that PSFs in the field are weaker than under controlled conditions. As expected, positive PSFs were more frequent as drought stress increased. The strongest OSRs were caused in dry plots by C4 perennial grasses, which had very positive OSRs on several C3 annual forbs, but negative effects on each other. Well-documented differences between these two functional groups may explain this result: C3 plants are more sensitive to drought, and thus may be favored by tolerance-conferring microbiota; in contrast, water-efficient C4 perennial grasses compete for phosphorus strongly, perhaps driving strong negative PSFs between them. Finally, close relatives had more negative OSRs on each other than on distant relatives as expected, although only in dry plots. This pattern was mostly due to the negative effects of closely related C4 grasses under dry conditions, and their positive effects on distantly related dicots. Our results highlight the importance of plant traits and of the environmental context in determining the direction and strength of PSFs under field conditions.

Effects of Phylogenetic Relatedness on Fluctuation-Dependent and Fluctuation-Independent Coexistence Mechanisms in Multispecies Communities.

AbstractEvolutionary relatedness may hinder stable coexistence due to similar niches and nonlinear responses to competition. The mechanisms driving stability may respond differently to phylogenetic distance. Related species may be synchronic (have similar demographic responses over time), affecting fluctuation-dependent mechanisms: the storage effect should destabilize coexistence, and relative nonlinearity should be stronger due to increased fluctuations in competition. We tested these hypotheses using invasion analysis based on a model parameterized for 19 plant species from a semiarid grassland. Although weakly, coexistence stability increased with phylogenetic distance. Stabilization through fluctuation-independent niche differentiation was stronger between distant relatives as a result of weaker competition. Synchronicity was higher between close relatives, having the expected negative effects on the storage effect's contribution to coexistence. Relative nonlinearity was strong at both ends of the phylogenetic relatedness gradient but not in the middle. This may be the result of different nonlinear responses between distant relatives and of stronger fluctuations in competition due to synchronicity between closer relatives. The effect of phylogenetic distance on coexistence was almost negligible when pairwise species were analyzed, in accordance with previous research. Phylogenetic distance became more important as more species interacted, however, suggesting that evolutionary relatedness may be influential in species-rich communities.

Tussocks facilitate their neighbours mainly by ameliorating extreme temperatures in tropical high mountains.

Facilitation by tussocks is common in high-altitude tropical environments. It is thought that facilitation results from stress amelioration, but it is unclear which of the many stressors acting in these environments is ameliorated. We aimed at determining the relative importance of different stressors as drivers of facilitation by the tussock Festuca tolucensis in Mexico. We employed eight experimental treatments to manipulate five stressors in the field: minimum temperatures by using electric radiators that kept plants warm; maximum temperatures by means of reflective sand that precluded temperature build-up during the day; UV radiation by using screens opaque to UV; poor soil properties by comparing soils from beneath tussocks and from bare ground; and low water availability by adding vermiculite to the soil. The performance (survival and growth) of Mexerion sarmentosum (a plant usually associated with Festuca) in these treatments was compared to that recorded under tussocks and in bare ground. Amelioration of extreme temperatures had the largest positive effects on Mexerion survival. UV radiation and increased soil humidity did not affect survival, although humidity increased growth rates. Nevertheless, tussocks reduced the growth of Mexerion, which is consistent with observations of competition between plants and soil microorganisms favoured by tussocks. Our results highlight the importance of the extreme daily fluctuations in temperature that characterise tropical mountains as fundamental drivers of their dynamics.

Efectividad de la succión desembrozante en pacientes con procesos inflamatorios de las glándulas salivales mayores / Effectiveness of the depleting suction in patients with inflammatory processes of the major salivary glands

Introducción: Las inflamaciones agudas y crónicas pueden afectar las glándulas salivales mayores. Objetivo: Evaluar la evolución de los pacientes con procesos inflamatorios de las glándulas salivales mayores tratados con succión desembrozante. Métodos: Se realizó un estudio descriptivo de 49 pacientes con procesos inflamatorios de las glándulas salivales mayores, atendidos en la consulta de Cirugía Maxilofacial del Hospital General Docente Dr. Juan Bruno Zayas Alfonso de Santiago de Cuba, desde septiembre del 2012 hasta junio del 2014. Se utilizó la aspiración quirúrgica para succionar los conductos de las glándulas salivales afectadas. Se estudiaron variables, tales como edad, sexo, glándula salival afectada, agente causal, sintomatología, sesiones de tratamiento y evolución ultrasonográfica. Resultados: Predominaron el grupo etario de 65 años y más (36,7 %) y el sexo femenino (59,2 %). La litiasis fue el factor causal de mayor incidencia y la glándula parótida la más afectada. Los pacientes evolucionaron satisfactoriamente luego de la segunda succión, lo cual demostró la existencia de cambios ultrasonográficos favorables. Conclusiones: La succión desembrozante es un procedimiento sencillo e inocuo que evita el proceder quirúrgico.

Introduction: The acute and chronic inflammations can affect the major salivary glands. Objective: To evaluate the clinical course of patients with inflammatory processes of the major salivary glands treated with depleting suction. Methods: A descriptive study of 49 patients with inflammatory processes of the mayor salivary glands was carried out, they were assisted in the Maxillofacial Surgery service of Dr. Juan Bruno Zayas Alfonso Teaching General Hospital in Santiago de Cuba, from September, 2012 to June, 2014. The surgical aspiration was used to suck the tubes of the affected salivary glands. Some variables were studied, such as age, sex, affected salivary gland, causal agent, symptomatology, treatment sessions and ultrasonographic course. Results: There was a prevalence of the 65 and over age group (36.7 %) and the female sex (59.2 %). Lithiasis was the causal factor of more incidence and the parotid gland the most affected one. Patients had a favorable clinical course after the second suction, which demonstrated the existence of favorable ultrasonographic changes. Conclusions: Depleting suction is a simple and innocuous procedure that avoids operation.

Fluctuation-independent niche differentiation and relative non-linearity drive coexistence in a species-rich grassland.

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 non-linearity (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.

Seed mass equalises the strength of positive and negative plant-plant interactions in a semi-arid grassland.

The interplay and balance between positive and negative interactions are important and recurrent topics in plant ecology. If facilitation occurs because benefactors ameliorate stress, such balance may be driven by seed mass because stress tolerance and competitive ability of plants, particularly seedlings, are positively correlated with seed mass. Thus, small-seeded, stress-intolerant species may require facilitation, but not large-seeded ones. This would equalise the magnitudes of opposite-signed interactions because in small-seeded species, positive effects of facilitators and negative effects of competitors should be strong, while both effects should be weak in large-seeded species. To test this idea, we assessed the effects of interactions with four associated species on different components of the performance of ten focal species. As expected, the largest facilitative and competitive effects were recorded in small-seeded species, and positive interactions had similar magnitudes to negative ones for any given seed mass, especially when performance was integrated into lifelong fitness. Furthermore, the fact that small-seeded species seem to be strongly facilitated may explain why they are not outcompeted by large-seeded species. This is an alternative to other hypotheses explaining the coexistence of plants with different-sized seeds. The close balance between opposite-signed interactions in the presence of stress may also explain why interactions have strong effects on individuals (that interact with only a few species), but seemingly weaker effects on populations, where interactions between many species would cancel out.

Inferring space from time: On the relationship between demography and environmental suitability in the desert plant O. rastrera.

Demographic analyses and ecological niche modeling (ENM) are two popular tools that address species persistence in relation to environmental conditions. Classic demography provides detailed information about the mechanisms that allow a population to grow or remain stable at a local scale, while ENM infers distributions from conditions suitable for species persistence at geographic scales by relating species' occurrences with environmental variables. By integrating these two tools, we may better understand population processes that determine species persistence at a geographic scale. To test this idea, we developed a model that relates climate to demography of the cactus Opuntia rastrera using 15 years of data from one locality. Using this model we determined the geographic area where populations would have positive growth rates given its climatic conditions. The climate-dependent demographic model showed poor performance as a distribution model, but it was helpful in defining some mechanisms that determine species' distributions. For instance, high rainfall had a negative impact on the population growth rate by increasing mortality. Rainy areas to the west of the distribution of O. rastrera were identified as unsuitable both by our climate-dependent demographic model and by a popular ENM algorithm (MaxEnt), suggesting that distribution is constrained by excessive rains due to high mortality. Areas projected to be climatically suitable by MaxEnt were not related with higher population growth rates. Instead, we found a strong correlation between environmental distance to the niche centroid (center of the niche hypervolume, where optimal conditions may occur) and population growth rate, meaning that the niche centroid approach is helpful in finding high-fitness areas.

Pseudoaneurisma de la fibrosa mitro aórtica en endocarditis de aorta bicúspide: A propósito de un caso / Pseudo-aneurism of the mitral aortic intervalvular fibrosa in a patient with bicuspid aortic valve endocarditis: A case report

El pseudoaneurisma de la fibrosa mitro aórtica es una complicación infrecuente pero potencialmente fatal de la endocarditis infecciosa de válvula aórtica. El diagnóstico de pseudoaneurisma se realiza mediante una técnica de imagen, principalmente la ecocardiografía transtorácica y transesofágica, en la que se evidencia una cavidad perivalvular pulsátil con expansión sistólica y colapso diastólico localizada en la zona mitro-aórtica. Por el riesgo de complicaciones, en la mayoría de pacientes, se recomienda el reemplazo de válvula aórtica con cierre del pseudoaneurisma. Se presenta un caso de pseudoaneurisma de la fibrosa mitro aórtica en un paciente adulto joven con endocarditis de válvula aórtica bicúspide. (AU)

Pseudoaneurysm of the mitral-aortic intervalvular fibrosa is an infrequent but potentially fatal complication of aortic valve endocarditis. Diagnostic is done by an imaging technique, especially transthoracic and transesophageal echocardiography, consisting of a pulsatile cavity with systolic expansion and diastolic collapse located in the mitral-aortic intervalvular fibrosa. Due to the risk of complications, aortic valve replacement and closure of the pseudoaneurysm is recommended. We present a case of pseudoaneurysm of the mitral-aortic intervalvular fibrosa in a patient presenting with bicuspid aortic valve endocarditis. (AU)

¿Cuánto saben los estudiantes del Grado en Medicina sobre la enfermedad de Chagas en España? / How much do Medicine students know about Chagas’ disease in Spain?

No disponible

Potassium enhances frost tolerance in young individuals of three tropical dry forest species from Mexico.

Movement of species outside their range of distribution could be a strategy for conservation purposes, but before implementation, it is necessary to evaluate plants responses to the conditions that they will experience in new locations. We evaluated the effect of potassium fertilisation to enhance the frost tolerance of young individuals of Albizia plurijuga (Standley) Britton & Rose, Cedrela dugesii S.Watson and Ceiba aesculifolia (Kunth) Britten & Baker f., which are all common species from tropical dry forests in Mexico. Plants were propagated in a shade-house and fertilised during 9 months with different concentrations of potassium (39, 189 and 528ppm). In frost simulations, plants were exposed to temperatures below 0°C during different time periods and frost injury was assessed by electrolyte leakage of leaf discs from young and old leaves. We observed that potassium fertilisation enhanced frost tolerance by reducing electrolyte leakage mainly in young leaves. We recorded plant re-sprouting ability after exposure to subzero temperatures over 45 days, finding notable differences among species: all individuals of C. dugesii sprouted, followed by some of A. plurijuga and finally just one of C. aesculifolia. Also, high potassium levels increased re-sprouting response. These species have a low frost tolerance, but potassium fertilisation seemed to be effective to enhance it for young individuals, increasing the probability of survival if plants are moved to colder areas than current habitats.

Relación entre los métodos clínico y de Moyers-Jenkins para la evaluación del apiñamiento dentario / Relationship between the clinical and Moyers-Jenkins methods for the evaluation of dental crowding

Se realizó un estudio descriptivo y transversal de 29 modelos de yeso de la arcada inferior que presentaron algún grado de apiñamiento, los cuales pertenecían a pacientes ingresados en el Departamento de Ortodoncia de la Clínica Estomatológica Provincial Docente "Mártires del Moncada" de Santiago de Cuba, desde octubre hasta diciembre del 2013, a fin de determinar la correspondencia entre los métodos clínico y de Moyers-Jenkins para la evaluación del apiñamiento dentario. Entre las variables analizadas figuraron: métodos de evaluación del apiñamiento, tipo de dentición y grado de apiñamiento dentario. Al analizar los 2 métodos predominaron los afectados con discrepancia severa; sin embargo, la mayoría de los que fueron evaluados como discrepancia ligera por el primero resultaron sin discrepancia al aplicar el segundo. Existió mayor precisión entre ambos métodos en las discrepancias moderada y severa.

A descriptive and cross-sectional study of 29 plaster cast of the lower arch that presented a degree of crowding was carried out, which belonged to patients admitted in the Orthodontics Department of "Mártires del Moncada" Teaching Provincial Stomatological Clinic in Santiago de Cuba, from October to December, 2013, in order to determine the correspondence among the clinical and Moyers-Jenkins methods for the evaluation of dental crowding. Among the analyzed variables there were: methods of evaluation of crowding, teething type and degree of dental crowding. When analyzing the 2 methods those affected with severe discrepancy prevailed; however, most of those that were evaluated as slight discrepancy by the first method were without discrepancy when applying the second one. Higher precision existed between both methods in the moderated and severe discrepancies.

Relación entre los métodos clínico y de Moyers-Jenkins para la evaluación del apiñamiento dentario / Relationship between the clinical and Moyers-Jenkins methods for the evaluation of dental crowding

Se realizó un estudio descriptivo y transversal de 29 modelos de yeso de la arcada inferior que presentaron algún grado de apiñamiento, los cuales pertenecían a pacientes ingresados en el Departamento de Ortodoncia de la Clínica Estomatológica Provincial Docente Mártires del Moncada de Santiago de Cuba, desde octubre hasta diciembre del 2013, a fin de determinar la correspondencia entre los métodos clínico y de Moyers-Jenkins para la evaluación del apiñamiento dentario. Entre las variables analizadas figuraron: métodos de evaluación del apiñamiento, tipo de dentición y grado de apiñamiento dentario. Al analizar los 2 métodos predominaron los afectados con discrepancia severa; sin embargo, la mayoría de los que fueron evaluados como discrepancia ligera por el primero resultaron sin discrepancia al aplicar el segundo. Existió mayor precisión entre ambos métodos en las discrepancias moderada y severa(AU)

A descriptive and cross-sectional study of 29 plaster cast of the lower arch that presented a degree of crowding was carried out, which belonged to patients admitted in the Orthodontics Department of Mártires del Moncada Teaching Provincial Stomatological Clinic in Santiago de Cuba, from October to December, 2013, in order to determine the correspondence among the clinical and Moyers-Jenkins methods for the evaluation of dental crowding. Among the analyzed variables there were: methods of evaluation of crowding, teething type and degree of dental crowding. When analyzing the 2 methods those affected with severe discrepancy prevailed; however, most of those that were evaluated as slight discrepancy by the first method were without discrepancy when applying the second one. Higher precision existed between both methods in the moderated and severe discrepancies(AU)

Cultural significance of wild mammals in Mayan and mestizo communities of the Lacandon Rainforest, Chiapas, Mexico.

BACKGROUND: Several ethnobiology studies evaluate the cultural significance (CS) of plants and mushrooms. However, this is not the case for mammals. It is important to make studies of CS allowing the comparison of cultural groups because the value given to groups of organisms may be based on different criteria. Such information would be valuable for wildlife preservation plans. In this study, the most culturally significant species of mammals from the Lacandon Rainforest (Chiapas, Mexico) for people from two Mayan-Lacandon and mestizo communities were identified. The reasons behind the CS of the studied species were explored and the existence of differences among the cultural groups was evaluated. METHODS: One hundred ninety-eight semi-structured and structured interviews were applied to compile socio-demographic information, qualitative data on CS categories, and free listings. Frequency of mention was a relative indicator to evaluate the CS of each species of mammal. Comparison of responses between communities was carried out through multivariate analyses. The non-parametric Mann-Whitney U test was used to compare the number of mentioned species by Lacandons and mestizos as well as different responses in the qualitative categories. A χ2 test was used to compare frequency of categories. RESULTS: 38 wild mammal species were identified. The classification and Principal Components Analyses show an apparent separation between Lacandon and mestizo sites based on the relative importance of species. All four communities mentioned the lowland paca the most, followed by peccary, white-tailed deer, armadillo, and jaguar. No significant difference was found in the number of mentioned species between the two groups. Eight CS categories were identified. The most important category was "harmful mammals", which included 28 species. Other relevant categories were edible, medicinal, and appearing in narratives. CONCLUSIONS: The data obtained in this study demonstrates the existence of differential cultural patterns in the relationships that Lacandon and mestizo groups establish with mammals. Species are deemed important either because they are eaten of because of the harm they cause. We suggest the incorporation of local conceptions about wild animals in conservation frameworks for the fauna in the Lacandon Rainforest.

Effects of harvest on the sustainability and leaf productivity of populations of two palm species in Maya homegardens.

Traditional management practices are usually thought to be sustainable. The Maya manage Sabal (Arecaceae) palms in homegardens, using their leaves for thatching. The sustainability of such production systems depends on the long-term persistence of palm populations, whereas resource availability also depends on the number of leaves on individual palms. We examined how leaf harvest affects Sabal yapa and S. mexicana population growth rates (λ) and leaf production, comparing traditional and alternative harvest regimes in terms of sustainability and productivity. Demographic, harvest and leaf production data were recorded for three years in two homegardens. We used general integral projection models linked to leaf-production models to describe population dynamics and productivity. Harvest had no effect on S. yapa's vital rates or on λ, but it changed the growth rate of individuals of S. mexicana, with a negligible impact on λ. Homegardens affected λ values, reflecting the species' ecological affinities. S. mexicana, introduced from mesic forests, required watering and shade; therefore, its population declined rapidly in the homegarden that lacked both water and shade. The λ of the xerophilic S. yapa was slightly larger without watering than with watering. Palms usually compensated for leaf extraction, causing the number of leaves harvested per individual to increase with harvest intensity. Nevertheless, traditional management is relatively mild, allowing standing leaves to accumulate but reducing the homegarden's yield. Apparently, the Maya do not seek to maximize annual production but to ensure the availability of large numbers of leaves in homegardens. These leaves may then be used when the entire roof of a hut needs to be replaced every few years.

Reconstructing shifts in vital rates driven by long-term environmental change: a new demographic method based on readily available data.

Frequently, vital rates are driven by directional, long-term environmental changes. Many of these are of great importance, such as land degradation, climate change, and succession. Traditional demographic methods assume a constant or stationary environment, and thus are inappropriate to analyze populations subject to these changes. They also require repeat surveys of the individuals as change unfolds. Methods for reconstructing such lengthy processes are needed. We present a model that, based on a time series of population size structures and densities, reconstructs the impact of directional environmental changes on vital rates. The model uses integral projection models and maximum likelihood to identify the rates that best reconstructs the time series. The procedure was validated with artificial and real data. The former involved simulated species with widely different demographic behaviors. The latter used a chronosequence of populations of an endangered cactus subject to increasing anthropogenic disturbance. In our simulations, the vital rates and their change were always reconstructed accurately. Nevertheless, the model frequently produced alternative results. The use of coarse knowledge of the species' biology (whether vital rates increase or decrease with size or their plausible values) allowed the correct rates to be identified with a 90% success rate. With real data, the model correctly reconstructed the effects of disturbance on vital rates. These effects were previously known from two populations for which demographic data were available. Our procedure seems robust, as the data violated several of the model's assumptions. Thus, time series of size structures and densities contain the necessary information to reconstruct changing vital rates. However, additional biological knowledge may be required to provide reliable results. Because time series of size structures and densities are available for many species or can be rapidly generated, our model can contribute to understand populations that face highly pressing environmental problems.

Evaluation of the degree of mycophilia-mycophobia among highland and lowland inhabitants from Chiapas, Mexico.

BACKGROUND: Mushrooms generate strong and contrasting feelings ranging from extreme aversion to intense liking. To categorize these attitudes, Wasson and Wasson coined the dichotomic terms "mycophilia" and "mycophobia" in 1957. In Mesoamerica these categories have been associated to ecological regions. Highland peoples are viewed as mycophiles, whereas lowland inhabitants are considered mycophobes. However, this division is based on little empirical evidence and few indicators. This study questioned whether mycophilia and mycophobia are indeed related to ecological regions through the evaluation of 19 indicators tested in the highlands and lowlands of Chiapas, Mexico. METHODS: The heterogeneity of attitudes toward mushrooms was explored in terms of ecological region and sociocultural variables. Information was obtained through structured interviews in 10 communities in Los Altos de Chiapas (highlands) and the Selva Lacandona (lowlands). We analyzed indicators separately through χ2 tests and multivariate techniques. The Mycophilia-Mycophobia Index was also used in the analysis. To assess which factors better explain the distribution of attitudes, we built 11 models using the Beta probability-density function and compared them with the Akaike Information Criterion. RESULTS: Most people had positive attitudes in both ecological regions. The classification and ordination analyses found two large groups comprising both highland and lowland towns. Contrary to expectation if mycophilia and mycophobia were mutually exclusive, all the fitted probability distributions were bell-shaped; indicating these attitudes behave as a continuous variable. The model best supported by data included occupation and ethnicity. Indigenous peasants had the highest degree of mycophilia. DISCUSSION: Results suggest the studied populations tend to be mycophilic and that their attitudes are not dichotomic, but rather a gradient. Most people occupied intermediate degrees of mycophilia. Despite there markable similarity in the degree of mycophilia between ecological regions, the Principle-Coordinates Analysis shows differences in the specific way in which people from either region establishes a cultural relationship with mushrooms. The comparison of models suggests that sociocultural variables explains the differences better than ecological regions do. The obtained results are evidence of mycophilia among lowlands inhabitants in the Mayan region and of the fact that the mycophilia-mycophobia phenomenon is not expressed as a bimodal frequency distribution.

Does retained-seed priming drive the evolution of serotiny in drylands? An assessment using the cactus Mammillaria hernandezii.

PREMISE OF THE STUDY: Serotinous plants retain their seeds for a long time. In deserts, retained seeds undergo hydration-dehydration cycles and thus may become primed. Priming enhances germination and seedling vigor. We test the hypothesis that serotiny evolves because it provides a site protected from predators in which seeds can become primed. Rainfall-cued dispersal of primed seeds may enhance this effect. METHODS: We tested this hypothesis with Mammillaria hernandezii through protein-content analyses; field and laboratory germination experiments with primed, unprimed, and retained seeds; and fitness estimations from demographic models. KEY RESULTS: Hydration-dehydration cycles induced priming, enhancing germination. Artificial priming and retention in the parent plant for 1 yr induced similar changes in seed protein patterns, suggesting that priming occurs naturally while seeds are retained. Under field conditions, germination of seeds retained for 1 yr more than doubled that of seeds of the same cohort that were not primed or that remained buried for 1 yr. The first seeds to germinate died rapidly. Serotinous plants whose seeds underwent priming had higher fitness than those whose seeds were in the soil seed bank or that did not experience priming. CONCLUSIONS: Priming in soil seed banks may be costly because of high predation, so seed protection during priming is sufficient to promote the evolution of serotiny. Bet hedging contributes to this process. Rapid germination of primed seeds that respond to brief rainfall events is disadvantageous because such rainfall is insufficient for seedling survival. Serotinous species counteract this cost by cueing dispersal with heavy precipitation.

Identifying the demographic processes relevant for species conservation in human-impacted areas: does the model matter?

The identification of the demographic processes responsible for the decline in population growth rate (λ) in disturbed areas would allow conservation efforts to be efficiently directed. Integral projection models (IPMs) are used for this purpose, but it is unclear whether the conclusions drawn from their analysis are sensitive to how functional structures (the functions that describe how survival, growth and fecundity vary with individual size) are selected. We constructed 12 IPMs that differed in their functional structure by combining two reproduction models and three functional expressions (generalized linear, cubic and additive models), each with and without simplification. Models were parameterized with data from two populations of two endangered cacti subject to different disturbance intensities. For each model, we identified the demographic processes that most affected λ in the presence of disturbance. Simulations were performed on artificial data and analyzed as above to assess the generality of the results. In both empirical and simulated data, the same processes were identified as making the largest contribution to changes in λ regardless of the functional structure. The major differences in the results were due to misspecification of the fecundity functions, whilst functional expression and model simplification had lesser effects. Therefore, as long as the demographic attributes of the species are well known and incorporated into the model, IPMs will robustly identify the processes that most affect the growth of populations subject to disturbance, making them a reliable tool for developing conservation strategies.