No abstract

Soil fauna is essential for ecosystem dynamics as it is involved in biogeochemical processes, promotes nutrient availability, and affects the animal communities associated with plants. In this study, we examine the possible relationship between the soil microarthropod community on foliage production and quality of the shrub Pittocaulon praecox. We also examine the arthropods associated to its foliage, particularly the size of the main herbivores and of their natural enemies, at two sites with contrasting vegetation cover and productivity. The diversity of soil microarthropods was assessed from soil samples collected monthly under P. praecox individuals over 13 mo. Specimens collected were identified to species or morphospecies. Shrub foliage productivity was evaluated through the amount of litter produced. Resource quality was assessed by the mean content (percentage by weight) of N, C, S, and P of 30 leaves from each shrub. The mean size of herbivores and their natural enemies were determined by measuring 20 adult specimens of each of the most abundant species. We found a higher species richness of soil microarthropods and foliar arthropods in the open site, although the diversity of foliage arthropods was lower in the closed site. Shrubs growing in the closed site tend to produce more, larger, and nutritionally poorer (lower nitrogen content) leaves than open site. Herbivores and their natural enemies were also larger in the closed site. We found a significant positive relationship between the diversity and species richness of foliar arthropods and the nitrogen content of leaves. In general, species richness and diversity of both the foliar and soil fauna, as well as the size of organisms belonging to higher trophic levels, were affected by vegetation cover and primary productivity at each site. These findings highlight the need to simultaneously consider at least four trophic levels (soil organisms, plants, herbivores, and natural enemies) to better understand the functioning of these systems and their responses to environmental changes.

The Pedregal de San Ángel Ecological Reserve (REPSA) is located in the central campus of the Universidad Nacional Autónoma de México (UNAM), in México City. Diversity and abundance of edaphic mites of the order Mesostigmata were estimated in two sites of REPSA. One site had scanty vegetation, due to human alterations, and was designated as “open site” (O), whereas the other had less altered, denser vegetation, being designated as “closed site” (C). Samples of soil and litter collected during the rainy and dry seasons of 2008 were processed for the extraction of mites of that group, which were then mounted and quantified by morphospecies. Mite abundance was much higher in site O, but the number of morphospecies was about the same in both sites. The same mite families were found in both sites. For each season and for both seasons considered together, Shannon diversity and Pielou´s evenness indexes were significantly higher in site C. Sörensen similarity coefficient between sites was high in both seasons, but higher in the dry season; considering both seasons together, similarity coefficient between sites was 94%. This indicates that anthropogenic alteration of the vegetation at REPSA, reducing the height of the vegetation and turning it less dense, was not sufficient to cause major alterations in Mesostigmata species composition.

Se evaluó el efecto de la cobertura vegetal en la producción y crecimiento de hojas de Pittocaulon praecox en dos sitios contrastantes, cerrado y abierto, en un matorral xerófilo. En cada sitio se registró longi­tud, número de hojas y crecimiento total, temperatura, humedad, concentración de CO2, y cantidad de hojarasca producida. Se hizo un análisis de varianza de medidas repetidas y una prueba de t. La menor temperatura (20,79 ± 2,8 °C), mayor concentración de CO2 (169,10 ± 12,19) y humedad (40,13 ± 8,26) se registraron en el sitio cerrado, donde los arbustos crecen más (t118 = 3,83, P = 0,0002), producen más hojas (86,21 ± 43,31 gr) y alcanzaron mayor tamaño. Se concluye que la cobertura vegetal influye en el crecimiento y producción de hojas de Pittocaulon praecox.

Este estudio tuvo como objetivo describir la diversidad y abundancia de los micro artrópodos edáficos, en relación con las características físicas y químicas de suelos bajo diferente uso y manejo, así como caracterizar su estructura en un área de minería pétrea o de cantera.  Para esto se estudiaron los ensamblajes de microartrópodos edáficos en cinco zonas con diferente uso de suelo: Bosque de Pino-Encino conservado (B), Bosque de Pino-Encino degradado (Z), Agrícola (V), Erosión (E), y Mina (M), en Sierra Nevada (Tepetlaoxtoc, México), su relación con parámetros físicos y químicos del suelo y su potencial como bioindicadores, utilizando los valores del índice QBS-ar, en zonas de minería pétrea. Se encontró correlación positiva y significativa con la abundancia y los porcentajes de humedad y materia orgánica del suelo. Se identificaron grupos descritos como bioindicadores, hiperparasitoides y depredadores en sitios más conservados que los que presentan mayor degradación. Los valores del índice QBS-ar fueron mayores en el área B. Se identificaron tres zonas, B, M y E, definidas por su aptitud para realizar acciones de rehabilitación ecológica y el potencial de los microartrópodos para ser integrados en los programas de manejo y estrategias de conservación y rehabilitación en áreas de minería pétrea.