Interactions between different biological forms of aquatic macrophytes in a eutrophic tropical reservoir in Northeastern Brazil / Interacciones entre las diferentes formas biológicas de los macrófitos acuáticos en un reservorio eutrófico tropical del Noreste de Brasil

Abstract: The aquatic plants and biological processes have different interactions and their knowledge may contribute to the understanding of environmental dynamics in wetlands. The aim of this study was to report the type of interactions that different biological forms of macrophytes stand in the eutrophic tropical reservoir of Penha reservoir, Northeastern Brazil. Data collection was captured every two months from October 2009 to October 2010, considering the hydrological cycle in one-year period. For this, twelve perpendicular transects (separated by 10 m) at the reservoir's water edge were defined; each transect had two plots of 625 cm² (25 x 25 cm, separated by one meter) from which samples were obtained. Plants were collected and transported in identified plastic bags for subsequent quantification of the dry weight biomass; additionally, pressed samples were made in the field for identification purposes. The relative interaction index (RII) was used to identify the existence of positive and/or negative interactions between the biomass of the biological forms of aquatic plants. Student's t-tests were used to analyze variations in the abiotic data and biomass over time, and to determine differences between the dry and rainy seasons. Pearson and Spearman correlation coefficients were calculated to determine correlations between the biological forms and the biomass of the macrophytes, as well as environmental variables and RII. In the dry season, the environment was mainly composed of floating macrophytes (1 013.98 g/m²), with mats of submerged macrophytes (98.18 g/m²) that demonstrated a range of positive (RII= 1.0) to negative (RII= -0.2) interactions. The biomass of emergent macrophytes increased throughout the dry season (4.87 to 106.91 g/m²) due to the nurse plant effect that served as a substratum (RII= 1.0). During the rainy season the biomass of submerged macrophytes was reduced by 97 % due to direct and indirect relationships (RII= -1.0) to other macrophytes. Rainfall and emergent plants contributed to a reduction in the biomass of floating macrophytes (19.16 g/m²). The emergence of a third group of plants (emergent) lead floating plants to occupy other areas and excluded submerged plants. Overall, the interactions among plants within ecosystems were not definite due to stand composition and seasonality. Rev. Biol. Trop. 65 (3): 1095-1104. Epub 2017 September 01.

Resumen: El conocimiento de las interacciones de las plantas acuáticas contribuye a la comprensión de la dinámica del ambiente (embalse Penha, Noreste Brasil). El objetivo del estudio fue reportar las posibles interacciones positivas y/o negativas que ocurren en los matorrales de macrófitos con distintos tipos de plantas, en un reservorio tropical eutrofizado. La recolección de los datos se hizo cada dos meses, desde Octubre 2009 hasta Octubre 2010, se consideró un ciclo hidrológico de un año. Fueron muestreados doce transectos perpendiculares a la orilla, separados 10 m entre ellos. En cada transecto se recolectaron dos cuadrículas de 625 cm² (25 x 25 cm) distantes 1 m uno del otro. Las plantas fueron retiradas y puestas en bolsas plásticas numeradas de acuerdo con el punto de recolección, para cuantificación del peso seco de la biomasa. En el campo se hizo el prensaje de las muestras para la identificación de las macrófitas. Se utilizó el índice relativo de interacciones (RII) para identificar la existencia de interacciones positivas y/o negativas entre las formas biológicas de las plantas acuáticas. Se uso el t Student para evaluar las variaciones de los datos abióticos y biomasa a lo largo del tiempo y determinar las diferencias entre las estaciones de lluvia y seca. Fueron calculados los coeficientes de correlación de Pearson y Spearman para determinar las correlaciones entre las formas biológicas y la biomasa de macrófitas, las variables ambientales y RII. En el período seco, el ambiente estaba compuesto principalmente por plantas flotantes (1 013.98 g/m²) y con la presencia de macrófitos sumergidos (98.18 g/m²), que demostraron interacciones variando de positivas (índice relativo de interacción - RII= 1.0) hasta negativas (RII= -0.2). La biomasa de macrófitos emersos aumentó a lo largo de la estación seca (4.87 to 106.91 g/m²) debido al efecto nodriza que sirve como substrato (RII= 1.0). En la estación lluviosa la biomasa de macrófitos sumergida se redujo 97 % debido a interacciones directas y indirectas (RII= -1.0) con otros macrófitos. La lluvia y los matorrales de plantas acuáticas contribuyen a la reducción en la biomasa de los macrófitos flotantes (19.16 g/m²). La aparición de un tercer grupo de plantas (emersas) llevan las flotantes a ocupar otros sitios y la exclusión de los macrófitos sumergidos. La interacción entre las plantas en el ecosistema evaluado no son rígidas debido a la composición de los matorrales y la estacionalidad.

High tolerance to high-light conditions for the protected species Ariocarpus kotschoubeyanus (Cactaceae).

We determined the seasonal ecophysiological performance under perennial plants and under high solar radiation for adult individuals from the 'living rock' cactus Ariocarpus kotschoubeyanus, which occurs equally under nurse plants and in open spaces. We evaluated the effective quantum yield of photosystem II (ΦPSII) and the dissipation of thermal energy [non-photochemical quenching (NPQ)] thorough the year. The maximum apparent electron transport rate (ETRmax) and the saturating photosynthetically active photon flux density for PSII (PFDsat) were also determined from rapid light curves. We found that although the ΦPSII was higher in shaded sites under potential nurse plants than in exposed sites, all values were close to the optimal value of 0.83. The high ΦPSII found for A. kotschoubeyanus plants suggests that they use a great proportion of the absorbed light for photosynthesis, under nurse plants as well as in open spaces. We also found higher NPQ values in exposed sites than in shaded ones but only in Autumn, thus reducing the risk of photoinhibition. In addition, the PFDsat was higher in exposed sites than in shaded ones in Spring, Summer and Autumn, but in Winter there were no differences between treatments. We also found high saturating light levels for ETR (PFDsat higher than 1378 µmol m-2 s-1) in all seasons but in winter for shaded and non-shaded plants. Our findings indicate that A. kotschoubeyanus plants use a great proportion of the light that they absorb for photosynthesis. This high tolerance to high-light conditions could explain why A. kotschoubeyanus do not show preferences for protected sites under nurse plants.

Myiarchus flycatchers are the primary seed dispersers of Bursera longipes in a Mexican dry forest.

We evaluated the seed dispersal of Bursera longipes by birds along a successional gradient of tropical dry forest (TDF) in southwestern Mexico. B. longipes is an endemic tree to the TDF in the Balsas basin. The relative abundance of frugivorous birds, their frequency of visits to B. longipes and the number of removed fruits were recorded at three study sites with different stages of forest succession (early, intermediate and mature) characterized by distinct floristic and structural elements. Flycatchers of the Myiarchus and Tyrannus genera removed the majority of fruits at each site. Overall, visits to B. longipes were less frequent at the early successional site. Birds that function as legitimate dispersers by consuming whole seeds and regurgitating or defecating intact seeds in the process also remove the pseudoaril from seeds, thereby facilitating the germination process. The highest germination percentages were recorded for seeds that passed through the digestive system of two migratory flycatchers: M. cinerascens and M. nutingii. Perch plants, mainly composed of legumes (e.g., Eysenhardtia polystachya, Acacia cochliacantha, Calliandra eryophylla, Mimosa polyantha), serve also as nurse plants since the number of young individuals recruited from B. longipes was higher under these than expected by chance. This study shows that Myiarchus flycatchers are the most efficient seed dispersers of B. longipes across all successional stages. This suggests a close mutualistic relationship derived from adaptive processes and local specializations throughout the distribution of both taxa, as supported by the geographic mosaic theory of coevolution.

Los bosques de Abies guatemalensis Rehder de San Marcos, Guatemala: una oportunidad para su restauración ecológica / The forests of Abies guatemalensis Rehder of San Marcos, Guatemala: an opportunity for ecological restoration

El pinabete, Abies guatemalensis Rehder, es una especie distribuida en las montañas altas de Guatemala. Según elConsejo Nacional de Áreas Protegidas (Conap), sus poblaciones se encuentran severamente fragmentadas. Porsu rareza y fragmentación, esta especie se encuentra protegida por el Convenio sobre el Comercio Internacional deEspecies Amenazadas de Fauna y Flora Silvestre (Cites), lo que pone en relieve la importancia de la recuperaciónde sus bosques para su debida conservación. El éxito de su establecimiento puede mejorase al sembrarla junto a plantas nodriza, que le ayudarían a sobrevivir a las condiciones secas del año y las heladas que se presentan en las zonas de mayor altitud del país durante los meses de noviembre a febrero. Este trabajo muestra las características físicas, químicas y de vegetación del área de tres bosques de pinabete (A. guatemalensis) de la parte alta de San Marcos. Además, presenta la propuesta de restauración ecológica estimulada simulando la sucesión vegetal del área. Se elaboraron mapas, y describieron tres bosques de pinabete y sus alrededores; se presenta el estudio de la composición química del suelo y la vegetación y su representación en diferentes etapas de sucesión vegetal. Además, se propone la recuperación de áreas alrededor de parches de bosque, consistente en establecer plantas arbustivas en lugares abiertos donde aún no hay; por su parte en aquellas áreas donde ya se encuentren arbustos, se propone utilizarlos como plantas nodriza para establecer árboles de varias especies buscando mantener biodiversidad deespecies arbóreas, en donde la teoría de la sucesión indica que el pinabete va a dominar al final. Esta propuesta hademostrado viabilidad porque es una práctica conocida fuera de bosques naturales en áreas de San Marcos paraestablecer el pinabete con fines comerciales, que aprovecha la sucesión vegetal natural del área.

The fir, Abies guatemalensis Rehder, is distributed in the highlands of Guatemala. According to the NationalProtected Areas Council (Conap), their populations are severely fragmented. For its rarity and fragmentation,it is protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora species(Cites), indicating the importance of the recovery of their forests for the proper conservation of the species. Thesuccess of his establishment may be enhanced to sow with nurse plants, which would help to survive the dryconditions of the year and frosts that occur in the higher elevations of the country during the months of Novemberto February. This work shows the features physical and chemical and vegetation in the area of three forests of fir (A. guatemalensis) of the top of San Marcos. In addition, the proposal of ecological restoration simulating plantsuccession in the area. Maps were drawn, and three fir forests and surrounding described; it is shown the study the chemical composition of soil and vegetation and their representation in different ages of plant succession. Further, it is proposed the recovery of areas around patches of forest, consting of which is establish shrubby plants in open spaces where there are not yet; in areas where bushes already are, it is proposed to use it as nurse plants to establish trees of various species seeking to maintain biodiversity of tree species, where the theory of succession indicates that the fir will dominate in the end. This proposal is feasible because as it is known outside natural forests inareas of San Marcos to establish the fir for commercial purposes, which uses the natural plant succession the area.

Facilitative plant interactions and climate simultaneously drive alpine plant diversity.

Interactions among species determine local-scale diversity, but local interactions are thought to have minor effects at larger scales. However, quantitative comparisons of the importance of biotic interactions relative to other drivers are rarely made at larger scales. Using a data set spanning 78 sites and five continents, we assessed the relative importance of biotic interactions and climate in determining plant diversity in alpine ecosystems dominated by nurse-plant cushion species. Climate variables related with water balance showed the highest correlation with richness at the global scale. Strikingly, although the effect of cushion species on diversity was lower than that of climate, its contribution was still substantial. In particular, cushion species enhanced species richness more in systems with inherently impoverished local diversity. Nurse species appear to act as a 'safety net' sustaining diversity under harsh conditions, demonstrating that climate and species interactions should be integrated when predicting future biodiversity effects of climate change.

Factors affecting establishment success of the endangered Caribbean cactus Harrisia portoricensis (Cactaceae)

Early plant stages may be the most vulnerable within the life cycle of plants especially in arid ecosystems. Interference from exotic species may exacerbate this condition. We evaluated germination, seedling survival and growth in the endangered Caribbean cactus Harrisia portoricensis, as a function of sunlight exposure (i.e., growing under open and shaded areas), different shade providers (i.e., growing under two native shrubs and one exotic grass species), two levels of predation (i.e., exclusion and non-exclusion) and variable microenvironmental conditions (i.e., temperature, PAR, humidity). Field experiments demonstrated that suitable conditions for germination and establishment of H. portoricensis seedling are optimal in shaded areas beneath the canopy of established species, but experiments also demonstrated that the identity of the shade provider can have a significant influence on the outcome of these processes. Harrisia portoricensis seedlings had higher probabilities of survival and grew better (i.e., larger diameters) when they were transplanted beneath the canopy of native shrubs, than beneath the exotic grass species, where temperature and solar radiation values were on average much higher than those obtained under the canopies of native shrubs. We also detected that exclusión from potential predators did not increase seedling survival. Our combined results for H. portoricensis suggested that the modification of microenvironmental conditions by the exotic grass may lower the probability of recruitment and establishment of this endangered cactus species. Rev. Biol. Trop. 60 (2): 867-879. Epub 2012 June 01.

Las etapas iniciales de las plantas parecen ser las más vulnerables de su ciclo de vida, especialmente en ecosistemas áridos. Interferencias de especies exóticas pueden exacerbar esta condición. Evaluamos la germinación, supervivencia y crecimiento de plántulas del cactus en peligro de extinción Harrisia portoricensis, en función de la exposición a la luz solar, diferentes proveedores de sombra, exclusión de potenciales depredadores y condiciones micro-ambientales variables. Los experimentos demostraron que las condiciones adecuadas para la germinación y el establecimiento de plántulas de H. portoricensis son óptimas en áreas de sombra, bajo el dosel de especies establecidas, pero también demostraron que la identidad de los proveedores de sombra puede tener una influencia significativa sobre los resultados de estos procesos y que la exclusión de depredadores no aumentó la probabilidad de supervivencia de las plántulas. Las plántulas de H. portoricensis tuvieron mayores probabilidades de supervivencia y crecieron mejor cuando fueron transplantadas bajo la sombra de los arbustos nativos que bajo la sombra del pasto exótico, donde la temperatura y la radiación solar fueron en promedio mucho mayores que las obtenidas bajo la sombra de los arbustos nativos. Nuestros resultados sugieren que las modificaciones de las condiciones micro-ambientales por este pasto exótico pueden disminuir la probabilidad de reclutamiento y establecimiento de esta especie en peligro.