Negative Correlation between Ant and Spider Abundances in the Canopy of a Bornean Tropical Rain Forest

Preliminary Study on Hourly Dynamics of a Ground-Dwelling Invertebrate Community in a Farmland Vineyard

We evaluated the hourly dynamics of ground-dwelling invertebrate communities in farmland using infrared camera traps between August and September 2022. No significant variations within 24 h nor between any two time points of each day were observed in the taxonomic richness and abundance of the entire community. However, the periods from 4:00 to 7:00 and 13:00 to 20:00 showed relatively high taxonomic richness, while those from 2:00 to 6:00 and 16:00 to 21:00 showed relatively high abundance. Millipede abundance varied significantly in a 24 h period, with higher abundance from 3:00 to 4:00 and 1:00 to 2:00. Additionally, slug, beetle, and grasshopper abundances were significantly higher from 22:00 to 23:00, 17:00 to 18:00, and 23:00 to 24:00, respectively. The abundance of other taxa did not show significant variations between any two time points of a day. Predominant generalist predators showed positive correlation in their activity times. These results suggest that significant variations within each 24 h period are uncommon at either community or taxa (except for millipedes) levels in farmland ground-dwelling invertebrates. Further, while most taxa had significantly preferred active hours, the total community did not. Therefore, hourly dynamics should be considered to understand biodiversity maintenance.

Root climbers may alter invertebrate communities on tree trunks: an indirect effect of lianas

Root climbers are a group of lianas which typically climb the host tree using adhesive roots and do not compete with the host for light. They are relatively more abundant in high-latitude forests and were recently documented to have no harmful effect on their host trees. Although previous studies have examined the direct negative effects of lianas on their host trees, little is known about potential indirect effects via effects on the animal and plant communities. Here, we aimed to determine the effects of root climbers on the animal and plant community composition of their host trunk and whether these alterations indirectly affect host trees. To answer these questions, we compared the invertebrate community, herbaceous plant presence, moss cover and herbivory rates in more than 22 pairs of host and control trees in cool-temperate forests in Hokkaido, Japan. We selected Quercus crispula Blume and Hydrangea petiolaris Sieb. et Zucc. as the study species. Generalised linear mixed models (GLMMs) were used to determine the influence of lianas on tree trunk communities and host trees. Our results showed that the presence of root climbers increased the abundance of Araneae and herbaceous plants and reduced the abundance of Formicidae on host trees, implying a reduction of herbivory on hosts. These results imply that liana presence may reduce the herbivory rate on the host tree, potentially by altering the trunk animal and plant community structure. Our results have implications for the understanding of the effects of lianas on host trees and their function in high-latitude forests.

Spatial covariance of herbivorous and predatory guilds of forest canopy arthropods along a latitudinal gradient

In arthropod community ecology, species richness studies tend to be prioritised over those investigating patterns of abundance. Consequently, the biotic and abiotic drivers of arboreal arthropod abundance are still relatively poorly known. In this cross-continental study, we employ a theoretical framework in order to examine patterns of covariance among herbivorous and predatory arthropod guilds. Leaf-chewing and leaf-mining herbivores, and predatory ants and spiders, were censused on > 1000 trees in nine 0.1 ha forest plots. After controlling for tree size and season, we found no negative pairwise correlations between guild abundances per plot, suggestive of weak signals of both inter-guild competition and top-down regulation of herbivores by predators. Inter-guild interaction strengths did not vary with mean annual temperature, thus opposing the hypothesis that biotic interactions intensify towards the equator. We find evidence for the bottom-up limitation of arthropod abundances via resources and abiotic factors, rather than for competition and predation.