EFECTO DE LA DENSIDAD Y TAMAÑO FLORAL SOBRE EL EXITO REPRODUCTIVO DE NOTHOSCORDUM GRAMINUM (ALLIACEAE

The size, form and color are signals used by flowers to attract their pollinators. Large and showy color flowers usuallyreceive higher pollinators visitation rates. According to the optimal forage theory, pollinators would tend to visitflower patches where they obtain the maximum reward regarding the energy expenditure in flower search. In highdensity patches, flowers are very close each other, hence, flower discrimination by pollinators would tend to be low.In low density patches, however, where the forage effort is greater, larger flowers are usually associated with higherrewards and would receive higher pollinators visitation achieving greater fitness than co-especifics with smallerflowers. In the present study we assessed the effects of flower density and size on the reproductive success (RS) ofNothoscordum gramineum. Four patches of different densities were delimited and the flowers size of the half ofindividuals at each patch was manually reduced. Results showed that RS was significantly greater in individuals withlarger flowers. Additionally, density has a positive effect on RS, especially in large size flowers. Nevertheless, fruitionsuccess reached maximum values in patches of intermediate density. Individuals with cut flowers did not varied the RSwith the variation of the density, suggesting that flower size is the most important attribute measured as advertisementby pollinators in N. gramineum. Our results do not support the hypothesis that in high density patches, flowerdisplays have low importance.El tamaño, la forma y el color son señales que utilizan las flores para atraer a sus polinizadores. Las flores que presentanun gran tamaño o alta vistosidad reciben una alta tasa de visitas de polinizadores. Según la teoría óptima de forrajeo, lospolinizadores tienden a visitar los parches donde disminuyan el esfuerzo del forrajeo y obtengan una mayor recompensa.En parches de la alta densidad las flores están agrupadas, razón por la cual la discriminación entre las flores tendería aser baja. Sin embargo, en parches de la baja densidad donde el esfuerzo de forrajeo es mayor, flores de mayor tamañorecibirían mayores tasas de visitas de polinizadores y manteniendo un mayor éxito reproductivo que individuos coespecíficos de menor tamaño. En el presente estudio determinamos el efecto de la densidad y del tamaño floral sobre eléxito reproductivo (ER) y el éxito de fructificación (EF) en la especie Nothoscordum gramineum. Cuatro parches dedistintas densidades fueron delimitados y el tamaño de las flores de la mitad de los individuos presentes en cada parchefue reducido manualmente. Los resultados demuestran que tanto la ER como EF son significativamente mayores en losindividuos con flores más grandes. Demostramos además que la densidad tiene un efecto positivo sobre el ER,principalmente en las flores de mayor tamaño. EF alcanzó valores máximos en los parches de densidades intermedias,disminuyendo en los de mayor densidad. Los resultados sugieren que el tamaño floral fue el atributo medido másimportante sobre la adecuación biológica de N. gramineum, debido a que los individuos de flores cortadas no respondieroncon la variación de la densidad. Nuestros resultados no permiten apoyar la hipótesis que en parches de alta densidad,los rasgos florales tendrían menor importancia, puesto que siempre ER y EF fueron mayores en flores enteras sinconsiderar la densidad, y las flores cortadas no demostraron un aumento en ER o EF con el aumento de la densidad

Natives and non-natives plants show different responses to elevation and disturbance on the tropical high Andes of Ecuador

The aim was to assess patterns of plant diversity in response to elevation and disturbance in a tropical mountain. The study area was located in north-central portion of the Eastern Cordillera of the Ecuadorian Andes, on a road from 1,150 m a.s.l. (Osayacu) to 4,000 (Papallacta). Along a mountain road spanning a wide altitudinal gradient, at 20 elevations we sampled three plots: one at the roadside and two perpendicular to the roadside. The relationship between elevation and species richness was assessed using linear and quadratic regressions, the effect of disturbance on species richness was determined by ANCOVA and a t test with parameters obtained from quadratic equations. Similarity of species composition among the roadside and sites distant was evaluated with the Chao-Jaccard and classic Jaccard similarity indices, the distribution of non-native species according to their origin were analyzed with linear and quadratic regression. The native species showed a linearly monotonic decrease with elevation, whereas non-natives showed a quadratic distribution. Disturbed areas had the greatest number of non-native species and lower native species richness, showing also a high floristic similarity; less disturbed areas showed the opposite. The non-native species of temperate origin were more numerous and showed unimodal elevational distribution, while species of tropical origin were few and decreased linearly with elevation. We conclude that in a tropical highland mountain range, native and non-native plant species respond differently to elevation: native species exhibit a monotonically linear decrease, and non-native species show a unimodal trend. Disturbance positively affects non-native species showing higher richness and fewer species turnover. In addition, the non-native species are located along of the elevational gradient in relation to their biogeographic origin

Generating Groups of Products Using Graph Mining Techniques

AbstractRetail industry has evolved. Nowadays, companies around the world need a better and deeper understanding of their customers. In order to enhance store layout, generate customers groups, offers and personalized recommendations, among others. To accomplish these objectives, it is very important to know which products are related to each other.Classical approaches for clustering products, such as K-means or SOFM, do not work when exist scattered and large amounts of data. Even association rules give results that are difficult to interpret. These facts motivate us to use a novel approach that generates communities of products. One of the main advantages of these communities is that are meaningful and easily interpretable by retail analysts. This approach allows the processing of billions of transaction records within a reasonable time, according to the needs of companies

EFECTOS COMPETITIVOS DE LAALOCTONA INVASORACENTAUREA SOLSTITIALIS L. SOBRE DOS ESPECIES CHILENAS DE BACCHARIS EN DIFERENTES ESTADOS DEL CICLO DE VIDA

Several studies have revealed a variety of mechanisms of invasion of alien plant species. However, little is known on howthose mechanisms and their associated effects on native species change across different life-cycle stages. Under controlledconditions, we assessed the interactions between the alien invasive species Centaurea solstitialis L. (Asteraceae) and twopioneer native species to the Chilean matorral; Baccharis linearis (Ruiz et Pav.) Pers. and B. paniculata DC. (Asteraceae).Competitive effects of the invader on natives were evaluated by combining different life-cycle stages: seed-seed, plantseed, and plant-plant. Seed germination of C. solstitialis was explosive and much faster than that of the native species.The presence of C. solstitialis (individuals or seeds) did not affect negatively the seed germination of the two Baccharisspecies. However, the presence of C. solstitialis plants significantly decreased the total biomass of Baccharis plants.Thus, the effect of C. solstitialis on Baccharis species depended on the life-cycle stage at which the interactions occurred.In the Chilean matorral, the early emergence of C. solstitialis could be an important invasion mechanism, enablingestablished plants to competitively displace late emerging seedlings of Baccharis species. The huge abundance of C.solstitialis in some disturbed matorrals suggests that seedling establishment of these two pioneer species could be limited.Varios estudios han revelado una variedad de mecanismos de invasión en las plantas alóctonas. Sin embargo, aún se conocepoco sobre cómo tales mecanismos y sus efectos asociados cambian a través de diferentes estados del ciclo vida. En esteestudio evaluamos, bajo condiciones controladas, el resultado de las interacciones competitivas entre la especie invasoraCentaurea solstitialis L. (Asteraceae) y dos especies pioneras nativas del matorral chileno; Baccharis linearis (Ruiz etPav.) Pers. y B. paniculata DC. (Asteraceae). Estas interacciones fueron evaluadas combinando diferentes estados delciclo de vida: semilla-semilla, planta-semilla y planta-planta. La germinación de C. solstitialis fue explosiva, siendo muchomás rápida que la de las especies nativas. La presencia de C. solstitialis (plantas o semillas) no disminuyó la germinaciónde las especies nativas de Baccharis. Sin embargo, la presencia de plantas establecidas de C. solstitialis disminuyósignificativamente la biomasa de las plantas de Baccharis. Entonces, el efecto de C. solstitialis sobre las especies deBaccharis varió en función del estado del ciclo de vida en el cual las interacciones ocurrieron. En el matorral chileno, laemergencia temprana y explosiva de C. solstitialis podría ser un importante mecanismo de invasión, ya que aquellasplantas prontamente establecidas podrían desplazar competitivamente a las plántulas de Baccharis que emergen mástarde. La enorme abundancia de C. solstitialis en algunas zonas de matorral sugiere que el establecimiento de plántulas deestas dos especies pioneras podría estar siendo limitado

Warmer Temperatures Affect the in situ Freezing Resistance of the Antarctic Vascular Plants

Although positive effects on growth and reproduction of Antarctic vascular plants have been reported under warmer temperatures, it could also increase the vulnerability of these plants to freezing. Thus, we assessed in situ whether warming decreases the freezing resistance of Colobanthus quitensis and Deschampsia antarctica, and we compared the level and mechanism of freezing resistance of these species in the field with previous reports conducted in lab conditions. We assessed the freezing resistance of C. quitensis and D. antarctica by determining their low temperature damage (LT50), ice nucleation temperature (NT) and freezing point (FP) in three sites of the King George Island. Plants were exposed during two growing seasons to a passive increase in the air temperature (+W). +W increased by 1K the mean air temperatures, but had smaller effects on freezing temperatures. Leaf temperature of both species was on average 1.7K warmer inside +W. Overall, warming decreased the freezing resistance of Antarctic species. The LT50 increased on average 2K for C. quitensis and 2.8K for D. antarctica. In contrast, NT and FP decreased on average c. 1K in leaves of warmed plants of both species. Our results showed an averaged LT50 of -15.3°C for C. quitensis, and of -22.8°C for D. antarctica, with freezing tolerance being the freezing resistance mechanism for both species. These results were partially consistent with previous reports, and likely explanations for such discrepancies were related with methodological differences among studies. Our work is the first study reporting the level and mechanisms of freezing resistance of Antarctic vascular plants measured in situ, and we demonstrated that although both plant species exhibited a great ability to cope with freezing temperatures during the growing season, their vulnerability to suffer freezing damage under a warming scenario increase although the magnitude of this response varied across sites and species. Hence, freezing damage should be considered when predicting changes in plant responses of C. quitensis and D. antarctica under future climate conditions of the Antarctic Peninsula

Conductancia hidráulica foliar y vulnerabilidad a la cavitación disminuyen con la altitud en Phacelia secunda J.F. Gmel. (Boraginaceae)

High mountain ecosystems are characterized by freezing temperatures. Freeze-thaw events can induce embolism in plant xylem. Therisk of embolism increases with the conduit diameter, because wider xylem vessels can contain larger amounts of dissolved gas thatafter water freeze may form big bubbles producing cavitation. Thus smaller vessels could be advantageous in habitats prone to freezingevents. However, smaller conduits decrease hydraulic conductance. The leaf hydraulic conductance (Kf) is a measure of the efficiencyin the water transport across the leaf, and it is defined as the ratio between the water flux across the leaf and the difference of hydraulicpotential across the leaf. Apparently, Kf is a bottleneck for hydraulic conductance of the whole plant and probably also a crucial factorin gas exchange. In this work we evaluated how the elevational origin of P. secunda can affect the hydraulic conductance of the leaf andthe cavitation vulnerability of the vessels. We postulate that plants of P. secunda from higher elevations, as exposed to higher frequencyof freezing events, have minor vessels diameter and lower Kf than plants from lower elevations. To test our hypothesis, we determinedunder field conditions the leaf hydraulic conductance (Kf), in plants from an altitudinal gradient (1,600, 2,800 and 3,600 m) in the central Chilean Andes. In addition, we analyzed cross sections of petiole and leaf lamina to evaluate the changes in the number, sizeand frequency of xilematic vessels in order to determine a cavitation vulnerability index. We found a negative correlation between thehydraulic conductance of the leaf and elevation in P. secunda plants. This is related to the smaller diameter of xylem vessels found inplants higher altitude, which results in a reduced vulnerability to cavitation. These changes could be considered as adaptives, because athigh elevations freezing events are more frequent, and hence, there is a higher probability of cavitation than at low elevations. However,this can negatively effect stomatal conductance and carbon assimilation, restricting the photosynthetic responses of these plants.Los ecosistemas de alta montaña se caracterizan por presentar temperaturas bajo cero durante gran parte del año. Estos episodiosde temperaturas bajo cero podrían inducir embolismo en las plantas que habitan estos ecosistemas ya que durante el congelamientose generan burbujas de aire, las que pueden expandirse durante el descongelamiento conduciendo a la cavitación. La probabilidadde embolismo o cavitación en un conducto xilemático es inversamente proporcional a su diámetro. Sin embargo, la reducción deldiámetro de los vasos, por pequeña que sea, disminuye considerablemente la conductividad de éstos. La conductancia hidráulica de lahoja (Kf) está definida como la proporción entre el flujo de agua a través de la hoja y la diferencia de potencial hídrico a través de esta.Kf es un cuello de botella para la conductancia hidráulica de la planta completa y probablemente es también uno de los factores másdeterminantes en el intercambio de gases. Dado que la intensidad y frecuencia de temperaturas congelantes cambia con la altitud, esimportante estudiar cómo influye la altitud de procedencia de las plantas en la estructura e hidráulica de la hoja y las consecuencias deesto en las probabilidades de embolismo. En este trabajo aprovechamos la amplia distribución altitudinal de la hierba perenne Phaceliasecunda para evaluar cómo cambia la conductividad hidráulica de la hoja y la vulnerabilidad a la cavitación con la altitud. Postulamosque en plantas de P. secunda provenientes de mayores altitudes, al estar expuestas a una mayor frecuencia de eventos congelantes,tienen un menor diámetro de vasos y con ello una disminución en la Kf comparado con plantas provenientes de menor altitud. Paraevaluar esta hipótesis se determinó la conductancia hidráulica foliar (Kf) en plantas provenientes de diferentes altitudes (1.600, 2.800y 3.600 m) en los Andes de Chile Central. Además, se realizaron cortes transversales de pecíolo y lámina para evaluar las variacionesen el número, tamaño y frecuencia de los conductos xilemáticos, y se determinó el índice de vulnerabilidad a la cavitación. Se encontróuna correlación negativa entre la conductancia hidráulica de la hoja y la altitud. Lo anterior se relaciona con los menores diámetros devasos xilemáticos encontrados en las plantas de mayor altitud, lo que trae como consecuencia una menor vulnerabilidad a la cavitaciónen dichas plantas. Lo anterior sugiere una ventaja adaptativa para estas plantas ya que a mayor elevación existe una mayor frecuenciade heladas y en consecuencia mayores probabilidades de cavitación. Sin embargo, esto podría tener un efecto negativo en las tasas deconductancia estomática y asimilación de carbono, disminuyendo el desempeño de estas plantas

Carpobrotus edulis (L.) N.E. Br. (Aizoaceae) y su presencia en la flora de Chile

The genus Carpobrotus was represented on the Chilean flora only by native species C. chilensis. However, we found that the speciesnative of South Africa C. edulis is naturalized in coastal areas. We report it for first time as an alien species for the Chilean territory.The genus Carpobrotus was represented on the Chilean flora only by native species C. chilensis. However, we found that the speciesnative of South Africa C. edulis is naturalized in coastal areas. We report it for first time as an alien species for the Chilean territory

Efecto del aumento de la temperatura en la fotosíntesis de una especie alto-andina en dos altitudes

High-alpine environments have been proposed as particularly vulnerable to global warming. The interaction of variablessuch as water deficit and temperature conditions may restrict gas exchange in high-alpine areas. Due to different abioticconstraints that occur at different elevations in the Andes of central Chile we hypothesize that the temperature increases willpositively affect the photosynthesis of the high-Andean plant Phacelia secunda at high elevation but it will be negativelyaffected by warming at lower elevations. In this study we evaluated the effect of increased environmental temperature onthe gas exchange of P. secunda at two contrasting elevations: 2900 m and 3600 m a.s.l. At each elevation we exposed sixindividuals of P. secunda to a passive warming system with “Open Top Chamber” (OTC) that increased air temperature onca. 3ºC. Other six individuals we selected in open areas and maintained as control on each elevation. At both elevations,on each selected individual (i.e. within and outside OTCs) we measured gas exchange and xylem water potential. At bothelevations air temperature was on average 3.5°C higher inside the OTC. In contrast, OTC reduced 28% the soil and xylemwater potential only at 2900 m. The increased temperature inside the OTC reduced 40.7% gas exchange rates at 2900 m,but increased it 24.4% at 3600 m. These differential effects of warming on photosynthetic rates were accompanied bychanges in stomatal conductance. This suggests that the effects of global warming on the photosynthesis of P. secunda attwo contrasting altitudes are related with the concomitant changes on drought at each elevation.Se ha propuesto que los ambientes de alta montaña son especialmente vulnerables al calentamiento global. La interacciónde variables como déficit hídrico y las condiciones de temperatura ambiental puede restringir el intercambio gaseosoen zonas de alta-montaña. Debido a las distintas limitaciones abióticas que se encuentran en un gradiente altitudinal, sepropone que el aumento de la temperatura afectará positivamente la fotosíntesis de la planta alto-andina Phacelia secundaen elevadas altitudes y negativamente a las plantas de bajas altitudes. En el presente estudio se evaluó el efecto del aumentode la temperatura ambiental sobre el intercambio gaseoso de P. secunda en dos altitudes: 2900 m y 3600 m. En cada altitudse expusieron seis individuos de P. secunda a un sistema de calentamiento pasivo denominado “Open Top Chamber” (OTC)que aumenta la temperatura del aire en ca. 3ºC. Adicionalmente, en cada altitud se seleccionaron otros seis individuos enespacios abiertos para utilizarlos como control y que se encontraban a 2 m de la OTC más cercana. En cada individuo semidió el intercambio gaseoso y el potencial hídrico xilemático. La temperatura ambiental fue en promedio 3,5°C mayordentro de las OTC en ambas altitudes. En contraste, el potencial hídrico del suelo y de las plantas se redujo un 28% alinterior de las OTC, pero sólo a 2900 m. En esta altitud, las tasas de fotosíntesis al interior de las OTC se redujeronun 40,7%, mientras que a 3600 m las tasas aumentaron un 24,4%. Los efectos diferenciales en las tasas de fotosíntesisdebido a la temperatura fueron acompañados con cambios en la conductancia estomática. Esto sugiere que los efectosdel calentamiento global sobre la fotosíntesis de P. secunda son contrastantes entre ambas altitudes debido a los efectossecundarios que éste tiene sobre la disponibilidad hídrica en cada altitud

Clustering properties of intermediate and high-mass Young Stellar Objects

We have selected 337 intermediate and high-mass YSOs ($1.5$ to $20$ M$_{\odot}$) well-characterised with spectroscopy. By means of the clustering algorithm HDBSCAN, we study their clustering and association properties in the Gaia DR3 catalogue as a function of stellar mass. We find that the lower mass YSOs ($1.5-4$ M$_{\odot}$) have clustering rates of $55-60\%$ in Gaia astrometric space, a percentage similar to the one found in the T Tauri regime. However, intermediate-mass YSOs in the range $4-10$ M$_{\odot}$ show a decreasing clustering rate with stellar mass, down to $27\%$. We find tentative evidence suggesting that massive YSOs ($>10$ M$_{\odot}$) often appear $-$yet not always$-$ clustered. We put forward the idea that most massive YSOs form via a mechanism that demands many low-mass stars around them. However, intermediate-mass YSOs form in a classical core-collapse T Tauri way, yet they do not appear often in the clusters around massive YSOs. We also find that intermediate and high-mass YSOs become less clustered with decreasing disk emission and accretion rate. This points towards an evolution with time. For those sources that appear clustered, no major correlation is found between their stellar properties and the cluster sizes, number of cluster members, cluster densities, or distance to cluster centres. In doing this analysis, we report the identification of 55 new clusters. We present tabulated all the derived cluster parameters for the considered intermediate and high-mass YSOs.Comment: Accepted for publication in The Astronomical Journal on August 18th, 2023. Table 1 and the new clusters can be provided upon reques