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.

Bacteria associated with Copestylum (Diptera, Syrphidae) larvae and their cactus host Isolatocereus dumortieri.

We describe the gut bacterial diversity inhabiting two saprophagous syrphids and their breeding substrate (decayed tissues of the columnar cactus Isolatocereus dumortieri). We analyzed the gut microbiota of Copestylum latum (scooping larvae that feed on decayed cactus tissues) and Copestylum limbipenne (whose larvae can also feed on semiliquid tissues) using molecular techniques. DNA was extracted from larval guts and cactus tissues. The V1-V3 region of the 16S rRNA genes was amplified and sequenced. A total of 31,079 sequences were obtained. The main findings are: C. limbipenne is dominated by several Enterobacteriaceae, including putative nitrogen-fixing genera and pectinolitic species and some denitrifying species, whereas in C. latum unclassified Gammaproteobacteria predominate. Decayed tissues have a dominant lactic acid bacterial community. The bacterial communities were more similar between larval species than between each larva and its breeding substrate. The results suggest that the gut bacterial community in these insects is not strongly affected by diet and must be dependent on other factors, such as vertical transmission, evolutionary history and host innate immunity.