Soil Microarthropods and Their Relationship to Higher Trophic Levels in the Pedregal de San Angel Ecological Reserve, Mexico

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.

EFECTO DE N6-BENCILADENINA Y FOTOPERIODO EN LA FLORACIÓN DE PROTOCORMOS in vitro DE Bletia urbana (ORCHIDACEAE)

“…Se usaron semillas de tres cápsulas dehiscentes de Bletia urbana colectadas en la Reserva Ecológica Pedregal de San Ángel (REPSA), ubicada al suroeste de la Ciudad de México (19° 14' a 19° 25' N y 99° 08' a 99° 15' W) y comprende 237 ha (Callejas-Chavero et al, 2015), registra una altitud de 2200 a 2277 msnm y presenta un clima templado subhúmedo, con una precipitación y temperatura promedio anual de 835 mm y 15.5 °C, respectivamente (Castillo et al, 2016). Las semillas recolectadas in situ se depositaron en un sobre de papel y se transportaron al IIAF-UMSNH.…”

Herbivory in Myrtillocactus geometrizans (Cactaceae): Do Parasitoids Provide Indirect Defense or a Direct Advantage?

“…Until recently, most studies on plant–insect interactions used to focus on direct relationships (plant–herbivore, plant–pollinator, or plant–disperser), overlooking other interactions between those these species. It is now recognized that, to gain a more comprehensive picture of plant–insect interactions and better understand their outcomes, lower and higher trophic levels (i.e., predators, parasitoids, hyperparasitoids, and decomposers) [ 2 , 3 , 4 ], as well as competitors [ 5 , 6 , 7 , 8 ], must be included.…”