Estructura de la comunidad de peces en cuatro estuarios del Pacífico mexicano central

ResumenSe analizó la estructura de la comunidad de peces y se determinaron algunos parámetros fisicoquímicos durante 4 colectas nocturnas en la desembocadura de los estuarios de barra de Nexpa, Teolán, Mexcalhuacán y barra de Pichi, Michoacán, México. Se capturaron un total de 2 014 individuos con un peso de 10 393.42g, pertenecientes a 31 especies y 20 familias. Barra de Nexpa registró la mayor riqueza con S=21 y el mayor porcentaje de especies raras con 22.6%. La especies con mayor abundancia fueron Agonostomus montícola y Mugil curema, mientras que Dormitator latifrons y Lutjanus novemfasciatus registraron la mayor biomasa. La salinidad, temperatura, oxígeno disuelto y transparencia mostraron diferencias significativas por temporadas, influidas por la variación estacional de la precipitación. La composición y especies dominantes fueron distintas en cada sitio y en cada temporada, mientras que la abundancia, biomasa y riqueza no mostraron variación significativa. La comunidad de peces estuvo compuesta por especies marinas y dulceacuícolas que utilizan los estuarios como zonas de crianza, especies marinas que se integran al estuario de manera ocasional y especies estuarinas que forman parte de estos ecosistemas durante la mayor parte de su ciclo de vida.AbstractCommunity structure of estuarine fish fauna were analyzed in estuaries of Barra de Nexpa, Teolán, Mexcalhuacán and Barra de Pichi, Michoacán, Mexico for four night collections at the mouth of every estuary. Also, some physicochemical parameters were determined. Were captured a total of 2 014 individuals with a weight of 10 393.42g, belonging to 31 species and 20 families. Barra de Nexpa recorded the highest richness (S=21) and the highest percentage of rare species (22.6%). The most abundant species were Agonostomus montícola and Mugil curema while Lutjanus novemfasciatus and Dormitator latifrons recorded the highest biomass. Salinity, temperature, dissolved oxygen and transparency, showed significant seasonal differences influenced by seasonal variation in precipitation. The composition and dominant species were different at each site and in each season while the abundance, biomass and richness showed no significant variation. The fish community was composed of marine and freshwater species that use estuaries as nursery areas, marine species that are incorporated into the estuaries occasionally and estuarine species that are part of these ecosystems for most of its life cycle

Insects as Stem Engineers: Interactions Mediated by the Twig-Girdler Oncideres albomarginata chamela Enhance Arthropod Diversity

Background: Ecosystem engineering may influence community structure and biodiversity by controlling the availability of resources and/or habitats used by other organisms. Insect herbivores may act as ecosystem engineers but there is still poor understanding of the role of these insects structuring arthropod communities. Methodology/Principal Findings: We evaluated the effect of ecosystem engineering by the stem-borer Oncideres albomarginata chamela on the arthropod community of a tropical dry forest for three consecutive years. The results showed that ecosystem engineering by O. albomarginata chamela had strong positive effects on the colonization, abundance, species richness and composition of the associated arthropod community, and it occurred mainly through the creation of a habitat with high availability of oviposition sites for secondary colonizers. These effects cascade upward to higher trophic levels. Overall, ecosystem engineering by O. albomarginata chamela was responsible for nearly 95 % of the abundance of secondary colonizers and 82 % of the species richness. Conclusions/Significance: Our results suggest that ecosystem engineering by O. albomarginata chamela is a keystone process structuring an arthropod community composed by xylovores, predators and parasitoids. This study is the first to empirically demonstrate the effect of the ecosystem engineering by stem-boring insects on important attributes o

Fish population responses to hydrological variation in a seasonal wetland in southeast México

ABSTRACT Hydrological variation differently affects fish species. In the present study, the response of local populations of 13 fish local species to hydrological variation in a tropical wetland was evaluated. The objectives were to analyze the abundance response of fish species with distinct life history strategies and to assess the role of hydrological variation on fish population patterns. We found that opportunistic strategists were favored by high hydrological variation in drought periods, the equilibrium strategists were related to stable habitats, and periodic strategists were regulated by floods and temperature. However, the life history strategies identified for some species in this study do not correspond to the classification reported in other studies. Our results highlight the importance to study the abundance responses of species at local and regional scales to identify variations in life-history strategies, which can reflect local adaptations of species to hydrological changes, this is useful in order to understand and predict the responses of fish populations to the local environment

Occurrence of termites (Isoptera) on living and standing dead trees in a tropical dry forest in Mexico

Termites play a key role as ecosystem engineers in numerous ecological processes though their role in the dynamics of wood degradation in tropical dry forests, particularly at the level of the crown canopy, has been little studied. In this study, we analysed the occurrence of termites in the forest canopy by evaluating the density and proportion of living and standing dead trees associated with termites in deciduous and riparian habitats of the tropical dry forest in Chamela, Mexico. The results indicated that 60–98% of standing dead trees and 23–59% of living trees in Chamela were associated with termites. In particular, we found that the density of standing dead trees was higher in deciduous forests (0.057–0.066 trees/m2) than in riparian forests (0.022 and 0.027 trees/m2), even though the proportion of trees was not significantly different among habitats. Additionally, we found a higher density of trees associated with termites in trees of smaller size classes (0.01–0.09 trees/m2) than in larger class sizes (0–0.02 trees/m2). Interestingly, 72% of variation in the density of trees associated with termites is explained by the density of standing dead trees. Overall, these results indicate that standing dead tree availability might be the main factor regulating termite populations in Chamela forest and suggest that termites could play a key role in the decomposition of above-ground dead wood, mediating the incorporation of suspended and standing dead wood into the soil

Fish diet composition in permanent and semi-permanent pools in tropical wetlands of the Yucatan Peninsula

We compared fish diet composition between permanent (P) and semi-permanent (SP) pools in Petenes Biosphere Reserve (PBR), Campeche. A total of 445 gut contents were examined to determine stomach relative fullness (RF), fish diet as index of niche breadth (INB) and diet overlap. In SP pools, species showed a RF of 1.66 (57.20 % empty stomachs) whereas in P pools, the RF was 2.91 (31.16%). We classified fish diet into six trophic groups: detritivorous, herbivorous-detritivorous, insectivorous, piscivorous, omnivorous and malacophagous. Species in P pools were found to be specialist. Conversely, species present in both habitats shifted to generalist patterns. There was a 54.0% dissimilarity in fish diet composition between pools. From all items identified, detritus (21.33% of the total dissimilarity), aquatic and terrestrial invertebrates (12.31%), fish remains (10.29%), plant remains (7.37%), and crustaceans (2.74%) distinguished diets between pools. Significant diet overlaps (>0.6) and low INB values (0.5) were observed. In SP pools seasonality had a strong effect on fish diet, increasing the frequency of food items such as terrestrial insects, amphipods and arachnids, during the rainy season while P pools showed lower variation. Thus, fish trophic habits appear to be regulated by pools hydrology

Effect of habitat engineering on branch colonization frequency by secondary colonizers.

<p>Data analyses were performed through a generalized linear model with a binomial distribution and a logit link function using a GLIMMIX procedure in SAS.</p

Abundance of secondary colonizers that emerged from <i>Spondias purpurea</i> detached branches.

<p>Bars indicate LSMeans (±SE) of the number of secondary colonizers that emerged per <i>S. purpurea</i> branch in the three studied years. White bars indicate non-engineered branches (NE); gray bars indicate simulated-engineered branches (SE); and black bars indicate <i>O. albomarginata chamela</i>-colonized branches (OE). Different letters indicate significant differences between treatments (P<0.05).</p

Secondary colonizers that emerged from <i>Spondias purpurea</i> branches detached and colonized by <i>Oncideres albomarginata chamela</i>.

<p>*Not recorded in 2007;</p>†<p>Life form I;</p>‡<p>Life form II;</p>§<p>Not recorded in non-engineered branches (NE); ND  = not determined. Abundance values are means across the three years (±SD).</p