Structure and histology of extrafloral nectaries of tropical species in a mexican rain forest / Estrutura e histologia dos nectarios extraflorais de especies em uma floresta tropical no México

Although there is a large diversity of plant species with extrafloral nectaries, histological detail of these glands is poorly documented in tropical rain forest species. We characterized extrafloral nectaries using digital photographs, scanning electron microscopy and histological methods for eight plant species belonging to the Costaceae, Euphorbiaceae, Malvaceae and Salicaceae. To our knowledge, there are no previous reports on the structure of extrafloral nectaries for these species. Croton species exhibited reddish extrafloral nectaries on the petioles, surrounded by starshaped trichomes. Cnidoscolus multilobus and Omphalea oleifera showed green, elevated, extrafloral nectaries at the peduncle; C. multilobus showed abundant secretory tissue; O. oleifera revealed numerous cells with calcium oxalate crystals. Heliocarpus species showed extrafloral nectaries distributed at the base of the blade and possesses glands in the center of the extrafloral nectary surrounded by a series of parenchymatic cells. Pleuranthodendron lindenii has two extrafloral nectaries at the base of the leaves. Costus scaber has a hollow-type extrafloral nectary on the red-colored bracts of the inflorescence; nectar cavity is found in the center area of each bracts located on a yellow line. The extrafloral nectaries described in this study exhibited different morphologies and histological structures involved in the secretion of extrafloral nectar that could be related to biotic defenses, primarily by attracting ants.

Embora exista uma grande diversidade de espécies de plantas com nectários extraflorais, detalhes histológicos destas glândulas ainda é pouco documentado para espécies tropicais. Nós caracterizamos nectários extraflorais usando fotografias digitais, microscopia eletrônica de varredura e métodos histológicos para oito espécies de plantas das famílias Costaceae, Euphorbiaceae, Malvaceae e Salicaceae. Para nosso conhecimento, não há relatos anteriores sobre a estrutura dos nectários extraflorais para as espécies estudadas. Espécies de Croton exibiram nectários extraflorais avermelhadas nos pecíolos, rodeados por tricomas em forma de estrela. Cnidoscolus multilobus e Omphalea oleifera apresentaram nectários extraflorais verdes e elevados nos pedúnculos; C. multilobus apresenta tecido secretor abundante enquanto que O. oleifera apresentou numerosas células com cristais de oxalato de cálcio. Espécies de Heliocarpus apresentaram nectários extraflorais distribuídos na base da lâmina e possuíam glândulas no centro do nectário rodeadas por uma série de células de parênquima. Pleuranthodendron lindenii apresentou dois nectários extraflorais na base das folhas. Costus scaber apresenta um nectário extrafloral do tipo oco nas brácteas avermelhadas da inflorescência, e a cavidade do nectário se encontra na área central de cada bráctea localizados em uma linha amarela. Os nectários extraflorais descritos neste estudo apresentaram morfologia e estruturas histológicas diferentes envolvidas na secreção de néctar extrafloral que poderia estar relacionado com defesas bióticas, principalmente atraindo formigas.

Impacto de las unidades de selva manejada tradicionalmente en la conectividad del paisaje de la Sierra de Los Tuxtlas, México / Impact of traditionally managed forest units on the landscape connectivity of Sierra de Los Tuxtlas, Mexico

The ever-increasing establishment of landscape mosaics is expressed as a surrounding matrix of agricultural activities, which frames patches or remnants of the original vegetation cover. Conservation actions should be aimed to establish or to increase those interactive systems, which help to maintain the landscape flow through linkages. Spaces occupied by traditional management systems retain and support this function. In this paper, we used Geographic Information Systems to evaluate the importance of traditionally managed forest units (‘acahuales’-coffee plantations) and to assess landscape connectivity in the indigenous Popoluca area of Sierra de los Tuxtlas, Mexico. The cartographic material used to establish the types of vegetation and their coverture included the period 1991-2008. At landscape level, four indices were used to assess the general situation of the habitat network, and to identify the patches of high priority. Individually, indices evaluated if patches were important for their area, their potential flow or their connecting function. Results showed that the landscape is functioning as a single system, but having low connectivity. Values improved when traditionally managed forest patches were considered as viable habitat. We detected 367 patches of very high priority, 80% belonging to forests managed traditionally. Patches were important for their potential flow (size and topological relationships). Only 70 patches were significant for their function as biological corridors between largest forests located at the top of the volcanoes, and are mostly managed forest (75%). We concluded that the units of traditionally managed forest play a significant role in landscape connectivity maintenance. Rev. Biol. Trop. 62 (3): 1099-1109. Epub 2014 September 01.

La existencia cada vez más frecuente de mosaicos de paisaje se expresa como una matriz circundante de actividades agropecuarias que enmarcan relictos de vegetación primaria. Cualquier acción de conservación debe de estar orientada a establecer o incrementar aquellos sistemas interactivos que mantengan los flujos del paisaje a través de enlaces. Los espacios ocupados por sistemas tradicionales de manejo favorecen y mantienen esta función. En el presente trabajo se evaluó, a través de un sistema de información geográfica, la importancia de las unidades de selva manejada de manera tradicional (acahuales-cafetales) en la conectividad del paisaje en la zona indígena Popoluca de la Sierra de los Tuxtlas, México. El material cartográfico utilizado para determinar los tipos de vegetación y su cobertura, abarca el periodo 1991-2008. Se emplearon cuatro índices para evaluar la conectividad a nivel paisaje y detectar cuáles son los fragmentos de muy alta prioridad para su mantenimiento. A nivel individual los índices evaluaron si los fragmentos son importantes por su área, por su flujo potencial o por su función conectora. Los resultados muestran que el paisaje funciona como un solo sistema, con baja conectividad. Los valores mejoran al incluirse la selva manejada como hábitat viable. Se detectaron 367 fragmentos de muy alta prioridad, 80% de ellos de selva manejada. Los fragmentos en su mayoría fueron importantes por el flujo potencial que representan (dimensiones y relaciones topológicas). Solo 70 fragmentos fueron importantes por su función como conectores, éstos actúan como corredores con las masas forestales de mayor tamaño localizadas en la cima de los volcanes, y son principalmente fragmentos de selva manejada (75%). Se concluye que las unidades de selva manejada de manera tradicional juegan un papel significante en el mantenimiento de la conectividad del paisaje.

Desplazamientos de la iguana verde, Iguana iguana (Squamata: Iguanidae) durante la estación seca en La Palma, Veracruz, México

Displacements of the green iguana (Iguana iguana) (Squamata: Iguanidae) during the dry season in La Palma, Veracruz, Mexico. The green iguana (Iguana iguana) is said to be primarily sedentary, although the females travel long distances to nest. Displacement patterns must be known to help predict the effects of environmental disturbance on iguanas’ survival. We studied nesting season (February-July) movements in La Palma, Los Tuxtlas, Veracruz, Mexico (18°33’ N, 95°03’ W). Individual movements and activity were monitored by radio tracking. The transmitters were implanted surgically in eight adult iguanas (four males and four females). Snout vent length (SVL) was used to determine the relationship between size of the body and size of home range. To estimate the size of home range, three or more points were used. Minimum convex polygons estimates of home range were calculated with McPAAL. The iguanas were radio-located between 23 and 30 occasions, mainly in trees (56 % between 3-9 m); only 4 % were localized under a height of 3 m (forest floor). The occupation area mean was larger for males (9 158.06±3 025.3m² vs. 6 591.24±4 001.1 m²) although the differences were not significant (t= 0.51, p>0.05). SVL was correlated with home range (r= 0.76; gl= 7; p<0.05). Breeding males defended their home range vigorously against other adult males. We observed one separate male home range and large portions of overlap between the sexes. The home range generally formed a conglomerate of polygons and only two had linear shapes along the river: apparently iguanas use the riparian vegetation for foraging. The females display two strategies for nesting: 1) moving to the sandy area near the sea or, 2) laying eggs near the river, in loam. Iguanas responded to habitat fragmentation and reduction by modifying their nesting strategy. Rev. Biol. Trop. 55 (2): 709-715. Epub 2007 June, 29.

Usamos radiotransmisores para determinar los desplazamientos de la iguana verde (Iguana iguana) en el periodo de anidación (febrero-julio) en La Palma, Los Tuxtlas, Veracruz, México (18°33’ N, 95°03’ W). Las iguanas fueron radiolocalizadas entre 23 y 30 ocasiones, principalmente en árboles (56 % entre 3-9 m); sólo 4 % fueron localizadas en el suelo. El tamaño del ámbito hogareño de machos y de hembras fue similar (9 158.06±3 025.3 m² vs. 6 591.24±4 001.1 m², respectivamente; t= 0.51, p>0.05). Se encontró una correlación significativa entre la LHC y el ámbito hogareño (r= 0.76, gl= 7, p<0.05). Las hembras tienen dos estrategias para anidar: 1) viajan para depositar los huevos a la arena de la playa, o 2) permanecen cerca de su ambiente ribereño y anidan en suelo arenoso-arcilloso. Al parecer, el ambiente fragmentado de la zona de la Palma, influye en la estrategia de anidación de la iguana verde.

Leaf and soil nitrogen and phosphorus availability in a neotropical rain forest of nutrient-rich soil

The nitrogen and phosphorus supply in a lowland rain forest with a nutrient-rich soil was investigated by means of the leaf N/P quotient. It was hypothesised a high N and P supply to the forest ecosystem with a N and P rich soil. Total N and extractable P were determined in the surface (10 cm) soil of three plots of the forest. Total N was analysed by the Kjeldahl method, and P was extracted with HCI and NH4F. The leaf N/P quotient was evaluated from the senesced leaves of 11 dominant tree species from the mature forest. Samples of 5 g of freshly fallen leaves were collected from three trees of each species. Nitrogen was analysed by microkjeldahl digestion with sulphuric acid and distilled with boric acid, and phosphorus was analysed by digestion with nitric acid and perchloric acid, and determined by photometry. Concentrations of total N (0.50%, n = 30) and extractable P (4.11 microg g(-1), n = 30) in the soil were high. As expected, P supply was sufficient, but contrary to expected, N supply was low (N/P = 11.8, n = 11).

A través del cociente foliar N/P, se investigó la disponibilidad de nitrógeno y fósforo en una selva húmeda tropical con suelo fértil. Como hipótesis se esperaba encontrar una alta disponibilidad de N y P en el ecosistema debido a un suelo rico en N y P. Se determinó el N total y el P extraible en el suelo superficial (10 cm) en tres sitios de la selva. El N total se analizó por el método Kjeldahl y el P por extracción con HCl y NH4F. El cociente foliar N/P se evaluó a partir de hojas seniles de 11 especies arbóreas dominantes de la selva madura. Se recolectaron muestras de 5 g de hojas recién caídas de tres árboles de cada especie. El nitrógeno se analizó por digestión microkjeldahl con ácido sulfúrico y destilación con ácido bórico, y el fósforo por digestión con ácido nítrico y ácido perclórico, y determinación con fotometría. Las concetraciones de N total (0.50%, n = 30) y P extraible (4.11 [mi]g g-1, n = 30) en el suelo fueron altas. Tal como se esperaba, la disponibilidad de P fue suficiente, pero contrariamente a lo esperado, la disponibilidad de N fue baja (N/P = 11.8, n = 11).

Pasture trees in tropical México: the effect of soil nutrients on seedling growth

Environment and seedling community under isolated trees in pastures are different from those in the open pasture. The effect of the pasture trees on the soil nutrients and on the seedling growth were investigated. Seven isolated trees and eight plots were selected in two pastures of 12-yr and 32-yr old derived from a lowland rain forest with nutrient-rich soil at Los Tuxtlas, Mexico. The soil concentrations of total N, P Bray, K+, Na+, Ca2+ and Mg2+, plus others physical and chemical characteristics, were compared between the pasture trees and the open-pasture. An experiment was done to test the hypothesis that soil from under the pasture trees was better for seedling growth than soil from the open pasture. Seedlings of two native tree species and two domesticated species were grown in soil from the two different sites in a shade-house. The dry weight of the shoot and root/shoot ratio were compared. Only total N, P and Na+ differed slightly in concentrations between the sites, but did not promote more seedling biomass. It seems that the soil at this location is sufficiently nutrient-rich even in the open pastures and over-ride any effect of the pasture trees on nutrient availability.

Los árboles aislados de los pastizales presentan un micro ambiente y comunidad de plántulas diferente a los del pastizal abierto. Se investigó el efecto de los árboles aislados en los nutrientes del suelo y en el crecimiento de plántulas. Se seleccionaron siete árboles aislados y ocho parcelas en dos pastizales de 12 y 32 años de edad, originados del cambio de uso de suelo de selva húmeda tropical con un suelo fértil, en Los Tuxtlas, México. Se compararon varias características físicas y químicas del suelo de los árboles y el pastizal abierto, así como las concentraciones de N total, P Bray, K+, Na+, Ca2+ y Mg2+. Se realizó un experimento para probar la hipótesis de que el suelo bajo los árboles aislados era mejor para el crecimiento de plántulas que el suelo del pastizal abierto. En un invernadero con suelo de los dos sitios diferentes, se pusieron a crecer plántulas de dos especies de árboles nativos y dos especies domesticadas. Se comparó el peso seco de la porción aérea de las plántulas y del cociente raíz/porción aérea. Solo difirieron ligeramente las concentraciones en suelo de N total, P y Na+ entre los sitios, pero estas no produjeron una mayor biomasa en las plántulas. Aparentemente el suelo en esta localidad es lo suficientemente rico en nutrientes aún en el pastizal abierto y opaca cualquier efecto de los árboles aislados del pastizal en la disponibilidad de nutrientes.