Sampling scarab beetles in tropical forests: the effect of light source and night sampling periods

Light traps have been used widely to sample insect abundance and diversity, but their performance for sampling scarab beetles in tropical forests based on light source type and sampling hours throughout the night has not been evaluated. The efficiency of mercury-vapour lamps, cool white light and ultraviolet light sources in attracting Dynastinae, Melolonthinae and Rutelinae scarab beetles, and the most adequate period of the night to carry out the sampling was tested in different forest areas of Costa Rica. Our results showed that light source wavelengths and hours of sampling influenced scarab beetle catches. No significant differences were observed in trap performance between the ultraviolet light and mercury-vapour traps, whereas these two methods caught significantly more species richness and abundance than cool white light traps. Species composition also varied between methods. Large differences appear between catches in the sampling period, with the first five hours of the night being more effective than the last five hours. Because of their high efficiency and logistic advantages, we recommend ultraviolet light traps deployed during the first hours of the night as the best sampling method for biodiversity studies of those scarab beetles in tropical forests.

El ecosistema de dehesa como reservorio de diversidad de insectos saproxílicos (Coleoptera y Diptera: Syrphidae) y factores que determinan sus ensambles

The “dehesa” (grassland with scattered oak trees) is a typical Mediterranean ecosystem from west Iberian Peninsula that has resulted from the transformation of the forest by clearing and brushwood removing and the landscape is maintained mainly bulls and/or Iberian pigs. This ecosystem is characterized by the presence of old scattered trees that are considered as “keystone-structures”, which favor the presence of a wide range of biodiversity, especially those species that are wood-dependent (saproxylic insects). Saproxylics are a diversified group involved in the recycling process of nutrients in forest, and thus they are considered as a bioindicator group of the quality and conservation status of habitats, including a wide number of species under some categories of threat according the IUCN criteria. It is widely recognized the importance of studying the main factors that determine the structure and distribution of species assemblages at both spatial and temporal scales, nevertheless, the saproxylic assemblages has been poorly studied from the temporal dimension. With this study we provide knowledge about the effect of the “dehesa” heterogeneity, species seasonality and distribution on this habitat and we highlight the importance of the maintaining of traditional practices as a tool for saproxylic insect diversity and conservation.

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.