Marco A. Molina-Montenegro

Efectos de la planta en cojín Oreopolus glacialis (Rubiaceae) sobre la riqueza y diversidad de especies en una comunidad alto-andina de Chile central

Las plantas en cojin que crecen en ambientes de alta montana modifican microclimaticamente su entorno, generando microhabitats favorables para el establecimiento de otras especies, actuando como nodrizas. Varios estudios han demostrado que los cojines contienen una mayor riqueza de especies que los espacios abiertos. Sin embargo, hasta ahora, no se ha evaluado el efecto de los cojines sobre otros parametros comunitarios como la abundancia de individuos, la diversidad y la equitatividad. En este trabajo se analiza el efecto que posee Oreopolus glacialis, una planta en cojin de la cordillera andina, sobre la riqueza, abundancia, diversidad y equitatividad de la comunidad vegetal en un ambiente de alta montana ubicado a 1.900 m en Chile central. Se determino la riqueza y abundancia de especies que crecen tanto sobre cojines de O. glacialis como en los espacios abiertos entre cojines. Los resultados mostraron que la riqueza de especies y la abundancia de individuos por unidad de area es mayor dentro de los cojines que fuera de ellos. Sin embargo, los valores de diversidad y equitatividad sobre O. glacialis fueron menores que fuera de ellos debido a la presencia de algunas especies dominantes. Analisis particulares de la frecuencia y abundancia de cada especie mostraron que no todas las especies son afectadas de la misma manera por la presencia de este cojin, por lo que O. glacialis actuaria como nodriza solo para una parte limitada de los componentes de la comunidad

Cushion Plants as Microclimatic Shelters for Two Ladybird Beetles Species in Alpine Zone of Central Chile

Abstract High mountain environments are highly stressful for insect survival. It has been suggested that small microtopographic variations generating less stressful microclimatic conditions than the surrounding environment would provide more suitable sites for insect development. Cushion plants represent one of the life forms best adapted to the extreme alpine habitats. Cushion plants can modify microclimatic conditions within and under their canopy, generating less severe microsites than the surrounding environment. In this study, we characterized the microclimatic modifications made by the cushion plants Azorella monantha and Laretia acaulis and examine their role as microclimatic shelters for two species of high Andean coleopterans (Coccinelidae): Eriopis connexa and Hippodamia variegata at 3200 m a.s.l. in the Andes of central Chile. Results showed that the cushion species create microhabitats with higher availability of water and less oscillating temperatures. However, the intensity of modifications was higher in A. monantha compared to L. acaulis. The abundance of the two ladybird beetle species was higher within cushions than outside, although E. connexa showed higher abundances compared to H. variegata. However, a habitat selection experiment in a greenhouse showed that under milder temperature conditions ladybird beetles species do not prefer cushions. This suggests that in the harsh alpine climate, cushion plants may act as microclimatic shelters since they reduce stressful environmental conditions, allowing greater abundances of coleopterans than in the surrounding environment.

Alpine dandelions originated in the native and introduced range differ in their responses to environmental constraints

Few studies have compared the response of native and invasive populations under stressful conditions. Furthermore, there is little consensus as to whether a plastic response is related to invasiveness in stressful environments. Exotic species have recently been reported in the high Andes of central Chile, where individuals have to cope with drought and poor soils, in addition to extreme temperatures. We explored if the exotic species Taraxacum officinale (dandelion) has plastic responses to soil moisture and nutrient availability, and whether two sets of alpine populations derived from native and introduced populations can converge to similar plastic responses to environmental constraints. Using a common garden approach, we compared plants grown from seeds collected in alpine populations of its native range (Alps, France) and in alpine populations of its introduced range (Andes, Chile) under a drought experiment, a potassium gradient, and a nitrogen gradient. Plasticity was only found as a response to drought. Moreover, different responses were found between both origins. Andean individuals are drought-resistant, while individuals from the Alps were drought-sensitive. According to the nutrient experiments, Andean dandelions behave as a nitrogen demanding-potassium avoiding species, whereas individuals from the Alps did not show any particular dependency or repulsion tendency to either of these two nutrients. Results suggest that differences in life history traits of both derived sets of populations may have an important role in determining the response of dandelions under the evaluated conditions. However, the relative importance of genetic adaptation in these responses is still unclear. Although T. officinale is a cosmopolite weed, this is the first study that compares individuals coming from its native and invaded range under stressful conditions.

Leaf litter of Kageneckia angustifolia D. Don (Rosaceae) inhibits seed germination in sclerophyllous montane woodlands of central Chile

Leaf litter accumulation can have either positive, negative or neutral effects on seed germination and seedling recruitment. In montane woodlands of the Mediterranean zone of central Chile, large amounts of leaf litter accumulate beneath the crowns of the summer semi-deciduous tree Kageneckia angustifolia and no regeneration of this or other plant species has been observed beneath this tree throughout the year. In a sample plot of 5000 m2 we selected ten K. angustifolia trees and measured (1) leaf litter accumulation beneath and outside canopy; (2) the effects of time elapsed since burial on viability of K. angustifolia seeds with and without a leaf litter cover; (3) field seed germination with presence or absence of leaf litter and (4) the possible chemical effects of K. angustifolia leaf litter leachates on seed germination of its own seeds and of other two co-occurring native shrubs species (Guindilia trinervis and Solanum ligustrinum). Our results show that a considerable accumulation of leaf litter occurred beneath K. angustifolia, and litter negatively affected seed viability and germination of this species in the field. Under laboratory conditions, K. angustifolia leaf litter leachates inhibited seed germination of its own seeds and of the two native shrub species. Chemical effects are likely involved in the negative effects of leaf litter on the recruitment of K. angustifolia in the montane sclerophyllous woodland of central Chile.

Photosynthetic performance of Colobanthus quitensis (Kunth) Bartl. (Caryophyllaceae) in a high-elevation site of the Andes of central Chile

Se estudio la fotosintesis de Colobanthus quitensis y las condiciones mesoclimaticas de temperatura del aire e intensidad luminica a 2.650 m en los Andes de Chile central. Se midio la tasa de intercambio gaseoso y la fluorescencia de la clorofila en tres dias tipicos durante la estacion de crecimiento (enero, marzo y mayo). Adicionalmente, se realizaron una serie de curvas de respuesta a incrementos en la intensidad luminica a diferentes temperaturas para estimar la propension de C. quitensis a la fotoinhibicion. La fotosintesis neta (Pn) fue baja (ca. de 2,0 mmol CO2 m-2s-1) en la manana y mediodia en dias con alta radiacion fotosinteticamente activa (PAR, sobre los 1.500 mmol fotones m-2s-1). La tasa de fotosintesis aumento en la tarde (3,5-4,8 mmol CO2 m-2s-1) cuando la radiacion PAR disminuyo a alrededor de 1.000 mmol fotones m-2s-1. Fv/Fm oscilo entre 0,7-0,75 en los registros de enero y marzo, decreciendo en mayo a 0,67. Hojas medidas a 15 y 22 °C mostraron un leve descenso en FPSII con el aumento en la intensidad de luz actinica, aunque la fraccion de centros de reaccion abiertos (expresados por qP) fue mayor a 22 °C. NPQ fue saturado a intensidades luminicas cercanas a 500 mmol photons m-2s-1 en hojas a 22 °C, y a intensidades mayores en hojas a 15 °C, sugiriendo que NPQ puede ser un mecanismo de disipacion energetica bajo condiciones de altas intensidades luminicas y altas temperaturas en el campo. Nuestros resultados indican que C. quitensis no sufre fotodano durante los ciclos diurnos, y probablemente, los bajos Pn registrados durante algunos periodos diurnos estan relacionados con fotorrespiracion, la cual ha sido sugerida como un mecanismo muy eficiente en la proteccion de plantas alpinas contra la fotoinhibicion. Nuestros resultados tambien son comparados con el desempeno fotosintetico de las poblaciones de C. quitensis en la Antartica maritima

Interactive Effects of Leaf Damage, Light Intensity and Support Availability on Chemical Defenses and Morphology of a Twining Vine

In a greenhouse study, we evaluated the effect of the light environment and support availability on the induction of tropane alkaloids (TAs) after leaf damage in the twining vine Convolvulus arvensis. We also tested whether leaf damage modifies the phenotypic responses of the plant to shade and physical support. We found a consistent pattern of induction of TAs after leaf damage in each environmental condition. The induction of TAs was differentially affected by combinations of support and light treatments. In the sun, prostrate and climbing vines exhibited similar induced responses. In the shade, prostrate vines showed greater induced responses. Thus, vines showed the greatest chemical induction when damage occurred in a resource-poor environment (shade), and there was no cue (support) of future increase in resource uptake. Damaged plants showed reduced plasticity to shading in leaf shape and internodes and petiole length in comparison with control, undamaged plants. Herbivory and/or induced responses to herbivory may limit adaptive plant responses to the environment. Therefore, the negative consequences of herbivory on plant fitness might be magnified in a context of changing environments.

Does global warming induce segregation among alien and native beetle species in a mountain-top?

The last few centuries have seen an increase in the mean air temperature of the planet, a phenomenon that is called “global warming”. One of the most sensitive habitats to the effects of global warming is the high-elevation mountain environments, because these habitats are characterized by low temperature. Cushion plants are one of the best-adapted growth forms in this habitat, generating more suitable sites for other plants and insects. In the present study, we experimentally evaluated the effects of global warming by open-top chambers on the abundance and interaction of two ladybirds at 3,600xa0m, growing over cushions of the Azorella monantha species in the Andes of central Chile. Additionally, we measured variation in temperature, water content, and food availability by the presence of open-top chambers as possible mechanisms of spatial segregation between ladybirds. Without open-top chambers, the abundance of native and alien beetles was similar; but with open-top chambers, the native beetle species is spatially segregated by alien species, decreasing in abundance. The open-top chambers increase temperature and food availability, but not water content. We suggest that under the global warming scenario, the native insects will decrease in abundance or become extinct by the presence of alien insects, at least in the high-elevation mountain environments.

Small-scale disturbances spread along trophic chains: leaf-cutting ant nests, plants, aphids, and tending ants

Small-scale disturbances caused by animals often modify soil resource availability and may also affect plant attributes. Changes in the phenotype of plants growing on disturbed, nutrient-enriched microsites may influence the distribution and abundance of associated insects. We evaluated how the high nutrient availability generated by leaf-cutting ant nests in a Patagonian desert steppe may spread along the trophic chain, affecting the phenotype of two thistle species, the abundance of a specialist aphid and the composition of the associated assemblage of tending ants. Plants of the thistle species Carduus nutans and Onopordum acanthium growing in piles of waste material generated by leaf-cutting ant nests (i.e., refuse dumps) had more leaves, inflorescences and higher foliar nitrogen content than those in non-nest soils. Overall, plants in refuse dumps showed higher abundance of aphids than plants in non-nest soils, and aphid colonies were of greater size on O. acanthium plants than on C. nutans plants. However, only C. nutans plants showed an increase in aphid abundance when growing on refuse dumps. This resulted in a similar aphid load in both thistle species when growing on refuse dumps. Accordingly, only C. nutans showed an increase in the number of ant species attending aphids when growing on refuse dumps. The increase of soil fertility generated by leaf-cutting ant nests can affect aphid abundance and their tending ant assemblage through its effect on plant size and quality. However, the propagation of small-scale soil disturbances through the trophic chain may depend on the identity of the species involved.

EFFECT OF DENSITY AND FLOWER SIZE ON THE REPRODUCTIVE SUCCESS OF NOTHOSCORDUM GRAMINUM (ALLIACEAE)

El tamano, la forma y el color son senales que utilizan las flores para atraer a sus polinizadores. Las flores que presentan un gran tamano o alta vistosidad reciben una alta tasa de visitas de polinizadores. Segun la teoria optima de forrajeo, los polinizadores tienden a visitar los parches donde disminuyan el esfuerzo del forrajeo y obtengan una mayor recompensa. En parches de la alta densidad las flores estan agrupadas, razon por la cual la discriminacion entre las flores tenderia a ser baja. Sin embargo, en parches de la baja densidad donde el esfuerzo de forrajeo es mayor, flores de mayor tamano recibirian mayores tasas de visitas de polinizadores y manteniendo un mayor exito reproductivo que individuos co-especificos de menor tamano. En el presente estudio determinamos el efecto de la densidad y del tamano floral sobre el exito reproductivo (ER) y el exito de fructificacion (EF) en la especie Nothoscordum gramineum. Cuatro parches de distintas densidades fueron delimitados y el tamano de las flores de la mitad de los individuos presentes en cada parche fue reducido manualmente. Los resultados demuestran que tanto la ER como EF son significativamente mayores en los individuos con flores mas grandes. Demostramos ademas que la densidad tiene un efecto positivo sobre el ER, principalmente en las flores de mayor tamano. EF alcanzo valores maximos en los parches de densidades intermedias, disminuyendo en los de mayor densidad. Los resultados sugieren que el tamano floral fue el atributo medido mas importante sobre la adecuacion biologica de N. gramineum, debido a que los individuos de flores cortadas no respondieron con la variacion de la densidad. Nuestros resultados no permiten apoyar la hipotesis que en parches de alta densidad, los rasgos florales tendrian menor importancia, puesto que siempre ER y EF fueron mayores en flores enteras sin considerar la densidad, y las flores cortadas no demostraron un aumento en ER o EF con el aumento de la densidad