EFFECT OF NECTAR-FORAGING ANTS AND WASPS ON THE REPRODUCTIVE FITNESS OF TURNERA ULMIFOLIA (TURNERACEAE) IN A COASTAL SAND DUNE IN MEXICO

We evaluated over two years the effect of different ant species on the reproductive fitness (estimated as end-of-season fruit set per treatment) of Turnera ulmifolia. Research was done on a sand dune matorral located on the coast of Veracruz, México. The results show that (i) plants associated with the larger ant species (Camponotus abdominalis) produced more fruits than plants associated with the smaller ant species, and (ii) plants associated with ants were subject to lower levels of herbivory, than plants without ants. Consequently, ant presence is not synonymous of plant protection, and the level of protection by ants will depend on the size of the worker ants in a guild of ant visitors. Moreover, when ants were excluded, wasps and bees increased their visits, exerting a higher level of protection than that offered by the smaller ant species. However, the differential effect of wasps needs further attention.Evaluamos durante dos años el efecto de diferentes especies de hormigas sobre el éxito reproductivo (estimado como número total de frutos por temporada) de Turnera ulmifolia. El estudio se llevó a cabo en el matorral de duna costera en la costa central del estado de Veracruz, México. Los resultados muestran que (i) plantas asociadas con la especie de hormiga más grande (Camponotus abdominalis) produjeron más frutos que plantas asociadas con las especies de hormiga más pequeñas, y (ii) plantas asociadas con las hormigas sufrieron niveles de herbivoría menores, que plantas sin hormigas. Consequentemente, la presencia de hormigas no es sinónimo de protección para una planta, y el nivel de protección por hormigas dependerá del tamaño de las hormigas obreras en un gremio de hormigas visitantes. Más aún, cuando se excluyeron a las hormigas, aumentaron las visitas de avispas y abejas, las que efectuaron un nivel de protección mayor que aquel ofrecido por las especies pequeñas de hormigas. Sin embargo, el efecto diferencial de las avispas requiere atención futura

Change in land use, forest management and its implications in the biotic interactions associated with Cedrela odorata Linnaeus, Meliaceae

Este trabajo documenta el efecto del manejo forestal en las interacciones planta-hormiga-herbívoro asociadas al cedro rojo Cedrela odorata L. 1759 en ecosistemas forestales del centro de Veracruz, México. Debido a la elevada demanda como madera preciosa y a la creciente explotación de su ecosistema, las plantaciones de C. odorata han sido promovidas. Asimismo, el establecimiento de plantaciones monoespecíficas y sus prácticas de manejo, ha propiciado el desequilibrio ecológico y el desarrollo de plagas. En las plantaciones de C. odorata la larva del insecto herbívoro conocido como barrenador de los tallos Hypsipyla grandella (Lepidoptera: Pyralidae) se ha convertido en una plaga de gran importancia económica. En este estudio, encontramos que en los sitios donde las prácticas de manejo forestal se efectuaron con mayor intensidad, la complejidad y composición de la vegetación adyacente a los árboles de C. odorata disminuyó, afectando también negativamente a la riqueza de la comunidad de hormigas, pero incrementando su abundancia. En las plantaciones la dominancia se concentra en un bajo número de especies de hormigas características de ambientes perturbados y tolerantes al manejo. La diseminación del daño causada por el barrenador del tallo es mayor en sitios con elevada intensidad de manejo, encontrando un patrón invertido en los sitios mejor conservados.This paper documents the effect of forest management on plant-ant-herbivore interactions associated with red cedar Cedrela odorata L. 1759 in forest ecosystems of central Veracruz, Mexico. Due to the high demand as precious wood and the growing exploitation of its ecosystem, the plantations of C. odorata have been promoted. Likewise, the establishment of monospecific plantations and their management practices has led to ecological imbalance and the development of pests. In the plantations of C. odorata the larvae of the herbivorous insect known as the shoot borer Hypsipyla grandella (Lepidoptera: Pyralidae) have become a pest of great economic importance. In this study, we found that in the places where forest management practices were carried out with greater intensity, the complexity and composition of the vegetation adjacent to the trees of C. odorata decreased, also negatively affecting the richness of the community of ants, but increasing its abundance. In plantations, dominance is concentrated in a low number of ant species characteristic of disturbed and tolerant environments. The dissemination of the damage caused by the shoot borer is greater in sites with high intensity of management, finding an inverted pattern in the best conserved sites

Interaction Intimacy Affects Structure and Coevolutionary Dynamics in Mutualistic Networks

The structure of mutualistic networks provides clues to processes shaping biodiversity [1-10]. Among them, interaction intimacy, the degree of biological association between partners, leads to differences in specialization patterns [4, 11] and might affect network organization [12]. Here, we investigated potential consequences of interaction intimacy for the structure and coevolution of mutualistic networks. From observed processes of selection on mutualistic interactions, it is expected that symbiotic interactions (high-interaction intimacy) will form species-poor networks characterized by compartmentalization [12, 13], whereas nonsymbiotic interactions (low intimacy) will lead to species-rich, nested networks in which there is a core of generalists and specialists often interact with generalists [3, 5, 7, 12, 14]. We demonstrated an association between interaction intimacy and structure in 19 ant-plant mutualistic networks. Through numerical simulations, we found that network structure of different forms of mutualism affects evolutionary change in distinct ways. Change in one species affects primarily one mutualistic partner in symbiotic interactions but might affect multiple partners in nonsymbiotic interactions. We hypothesize that coevolution in symbiotic interactions is characterized by frequent reciprocal changes between few partners, but coevolution in nonsymbiotic networks might show rare bursts of changes in which many species respond to evolutionary changes in a single species. © 2007 Elsevier Ltd. All rights reserved

Composición y estructura arbórea de petenes en la Reserva de la Biosfera de Los Petenes, Campeche, México

Analizamos la composición y estructura de la vegetación de 11 petenes de la Reserva de la Biosfera Los Petenes, Campeche. En cada petén seleccionamos cinco parcelas de 20 m x 20 m (400 m², total de 2000 m2) donde registramos todos los individuos leñosos con un diámetro a la altura del pecho (DAP) = 5cm. Se describe la estructura de cada petén con base en los valores relativos de densidad, frecuencia y dominancia (VIR), así como la distribución de clases diamétricas. Se estimó la diversidad por petén usando el índice de Shannon-Wiener (H’). Se estimó la similitud florística entre petenes usando el índice de Morisita. Registramos 2 927 individuos de 32 especies leñosas, en 29 géneros y 23 familias. Las familias con mayor número de géneros y especies fueron Fabaceae (3/3) y Sapotaceae (3/3). Entre las especies que presentaron mayor densidad están Metopium brownei, Manilkara zapota y Laguncularia racemosa. La distribución en clases de frecuencia usando el DAP, muestra que la mayoría de los individuos se agrupan en las clases inferiores. Con base en el VIR, las especies más importantes en la vegetación de los petenes son: Laguncularia racemosa (128.43), Metopium brownei (128.34) y Manilkara zapota (110.89). Con base en la similitud de especies, el área se dividió en dos grupos: Grupo Centro (petenes 5-11) y Grupo Norte (petenes 1-4). Los petenes 1 y 3 (Grupo Norte) fueron similares entre sí (98%), mientras que los petenes 5 y 7 (94%) lo fueron para el Grupo Centro. Los valores de diversidad mostraron que el petén 5 fue el más diverso (H’= 3.54, Grupo Centro) y el petén 1 (H’= 2.44, Grupo Norte). Independientemente del grado de perturbación, las especies leñosas características de los 11 petenes fueron Metopium brownei y Manilkara zapota y la palma Sabal yapa

Association Patterns in Saproxylic Insect Networks in Three Iberian Mediterranean Woodlands and Their Resistance to Microhabitat Loss

The assessment of the relationship between species diversity, species interactions and environmental characteristics is indispensable for understanding network architecture and ecological distribution in complex networks. Saproxylic insect communities inhabiting tree hollow microhabitats within Mediterranean woodlands are highly dependent on woodland configuration and on microhabitat supply they harbor, so can be studied under the network analysis perspective. We assessed the differences in interacting patterns according to woodland site, and analysed the importance of functional species in modelling network architecture. We then evaluated their implications for saproxylic assemblages’ persistence, through simulations of three possible scenarios of loss of tree hollow microhabitat. Tree hollow-saproxylic insect networks per woodland site presented a significant nested pattern. Those woodlands with higher complexity of tree individuals and tree hollow microhabitats also housed higher species/interactions diversity and complexity of saproxylic networks, and exhibited a higher degree of nestedness, suggesting that a higher woodland complexity positively influences saproxylic diversity and interaction complexity, thus determining higher degree of nestedness. Moreover, the number of insects acting as key interconnectors (nodes falling into the core region, using core/periphery tests) was similar among woodland sites, but the species identity varied on each. Such differences in insect core composition among woodland sites suggest the functional role they depict at woodland scale. Tree hollows acting as core corresponded with large tree hollows near the ground and simultaneously housing various breeding microsites, whereas core insects were species mediating relevant ecological interactions within saproxylic communities, e.g. predation, competitive or facilitation interactions. Differences in network patterns and tree hollow characteristics among woodland sites clearly defined different sensitivity to microhabitat loss, and higher saproxylic diversity and woodland complexity showed positive relation with robustness. These results highlight that woodland complexity goes hand in hand with biotic and ecological complexity of saproxylic networks, and together exhibited positive effects on network robustness.The research Projects I+D CGL2011-23658 y CGL2012-31669 of the Spanish Minister of Science provided economic support

La fuerza del amor en el Neotrópico: contraste en la eficiencia defensiva de dos especies de hormigas del género Pseudomyrmex sobre plantas de Acacia cornigera. (Parte I)

For years in the Neotropics has been impossible not to pay attention to one of the most recognized mutual interactions between some plants of the genus Acacia and Pseudomyrmex ants. For this first review, I present the maintenance of the interaction of plants with two Pseudomyrmex ant species with apparent differences in defensive behavior in a seasonal forest in Mexico. Following an observational methodology in the field, we found that there is a contagion colonization effect of plants. Moreover, the mayority of plants and also the largest ones were colonized with P. ferrugineus showing indirectly that they have a better defensive efficiency on their host plants to ants compared to P. gracilis. The obtained results are the starting point for the development of this research in which I will try to find what are the mechanisms that allow the coexistence of two species of ants in the study area

NUMERO Y VARIACION ESTACIONAL DE ASOCIACIONES HORMIGA-PLANTA EN UN BOSQUE MONTANO BAJO DE VERACRUZ, MEXICO

We quantified the number and seasonal variation of ant-plant associations mediated by néctar and homopteran honeydew in a low montane forest near Xalapa, Veracruz, México. We registered five ant specíes and 12 specias of angiosperms in 17 associations; we did not find obligate associations. Ant species differentially used the avaílable food resources: they used extrafloral néctar more, and floral néctar and honeydew less. The generalizad linear modal adjusted to the ant-plant associations curve explained 29% of the total variation. Precipitation alone explained 14%, and the interaction between factors (precipitation-temperature) explained 15% of the variation. Our results indicate that: (1) a low proportion of plants assocíated with anta in the low montane forest studied; (2) the environmental factors considered do not explatn the seasonal variation and the number of ant-plant associations; and (3) the low number of ant-plant associations is probably due to the low percentage of plant species bearing extrafloral nectaries, this beíng the result of an abundance of Holarctic or températe elements.Se cuantificó el número y la variación estacional de las asociaciones hormiga-planta en un bosque montano bajo cerca de Xalapa, Veracruz, México. Registramos cinco especies de hormigas y 12 especies de angiospermas en 17 asociaciones. No se encontraron asociaciones obligatorias. Las especies de hormigas utilizaron de manera diferencial los recursos alimenticios disponibles; usaron significativamente más el néctar extrafloral y menos el néctar floral y la ambrosía. Un modelo lineal generalizado ajustado a la curva de asociaciones hormiga-planta explicó el 29% de la variación. El 14% es explicado por la precipitación y el 15% por la interacción entre factores (precipitación-temperatura). Los resultados indican que: (1) en el bosque montano bajo estudiado la proporción de plantas asociadas con hormigas es baja; (2) los factores ambientales considerados no explican la variación estacional en el número de asociaciones hormiga-planta; y (3) el bajo número de asociaciones hormiga-planta encontrado, probablemente se debe al bajo porcentaje de especies que presentan nectarios exraflorales en la vegetación, producto de la dominancia de elementos florísticos holárticos o templados

Contraste en la eficiencia defensiva de dos especies de hormigas del género Pseudomyrmex sobre plantas de Acacia cornigera (Parte III)

One of the most emblematic mutualistic interactions in the Neotropics is that between Acacia plants and Pseudomyrmex ants. In his first studies, D. H. JANZEN (1969) related the functional defensive system by the ants to allelopathic chemical agents, thus this system can be associated to induced defensive systems. Our study system, the interaction between Acacia cornigera and two Pseudomyrmex species (P. gracilis and P. ferrugineus), includes ant colonization patterns and plant behavior after colonization. Previous research on ant defensive roles had mentioned that P. ferrugineus was a good defensive system for Acacia plants, and that P. gracilis was a so-called parasite of the system. Here we suggest that the subsistence mechanism between the two ant species is based on chemical products, clear postdamage signals which, are intrinsic to the plant and promote recruitment and defense by the two species of Pseudomyrmex