Date Published: April 12, 2019
Publisher: Public Library of Science
Author(s): Alfredo Ramírez-Hernández, Ana Paola Martínez-Falcón, Estefanía Micó, Sandra Almendarez, Pedro Reyes-Castillo, Federico Escobar, Fabio de Oliveira Roque.
We studied the saproxylic beetle community inhabiting deadwood in remnants of riparian cloud forests in “La Antigua” basin, in central Veracruz (Mexico). We assessed the influence of deadwood features (tree species, trunk position, trunk diameter, trunk volume and decomposition stages) on saproxylic beetle diversity. In order to assess the stability of beetle species-deadwood interactions, we also analyzed the ecological networks structure. A total of 63 deadwood trunks, belonging to four tree species, were sampled by standardized hand-collection throughout well-preserved remnants of riparian cloud forest. We found that tree species and deadwood decay stage are the main drivers that determine the diversity and stability of saproxylic beetle species interactions. Our results indicate that Quercus corrugata is the main tree species in terms of maintaining the significantly highest saproxylic beetle diversity, but with no stable interactions (saproxylic beetle-deadwood). A nested network structure was detected for Clethra mexicana and Liquidambar styraciflua, with a pool of core (generalist) saproxylic beetle species. We observed that beetle diversity from the early and late deadwood stages comprises distinct assemblages and the four stages of decomposition showed a nested network structure. During deadwood succession, community composition and guilds changed among networks; the early successional stage had more specialized xylophagous beetles, while other guilds (mycophagous, saprophagous and zoophagous) arrive later and become the core species in the advanced stages of decomposition networks. Heliscus tropicus (Passalidae) is a key species constituting the core of all of the networks and could be considered an ecosystem engineer in cloud forests. By exploring links between saproxylic beetles and deadwood characteristics, we can further our understanding of species interaction in order to develop management strategies oriented towards the protection of species and their habitats in this threatened ecosystem.
Deadwood has been widely studied over the last few decades [1,2] due to its contribution to maintaining functional biodiversity in forest environments [3,4–6]. Saproxylic (deadwood-dependent) species stand out as key organisms involved in the complex trophic webs of forests and other wooded environments, including some human modified habitats, such as crops with trees (e.g. shade coffee) and commercial plantations, among others [6–8]. During wood degradation, saproxylic beetles fulfilling important ecological functions  as a result of their capability to rapidly transform the physical-chemical properties of the microenvironment in which they develop their life cycle, directly influencing soil fertility and therefore also other saproxylic taxa [9–11].
From 63 deadwood pieces (49 logs and 14 stumps) belonging to four tree species, a total of 387 individuals and 44 saproxylic beetle species (21 morphospecies), belonging to nine families (Carabidae, Dynastidae, Leiodidae, Passalidae, Ptilodactylidae, Scarabaeidae, Staphylinidae, Tenebrionidae and Zopheridae) of saproxylic beetles, were collected (S4 Table). The richest families were Staphylinidae (18 species) and Carabidae (9 species), while the most abundant were Passalidae (171 individuals) and Staphylinidae (156 individuals). With regard to the most abundant beetle species, we found Heliscus tropicus (Percheron, 1835) represented by 41% (Passalidae) of the individuals collected, followed by Osorius sp.1 with 17% (Staphylinidae). In addition, a total of 17 species (39%) were recorded at very low frequencies (S4 Table).
As we hypothesized, our results provide evidence that host tree species and deadwood decomposition stage are the main drivers of the saproxylic beetle diversity in tropical cloud forest in central Veracruz, Mexico. This is consistent with findings in saproxylic beetle communities inhabiting deadwood in forests from other latitudes . Regarding patterns in ecological networks, our results coincides with Quinto et al  where tree species influence the network structure promoting a nested pattern. Saproxylic diversity was higher in Q. corrugata; however, this tree species does not support stable species interactions. The saproxylic network structure was thus significantly nested for both C. mexicana and L. styraciflua. Moreover, the four deadwood stages showed differences in species diversity and, in all cases, the networks were nested. In general, our findings agree with those of Muñoz-López et al , who reported a similar diversity pattern in a tropical deciduous forest of central Mexico.