Incorporating biotic interactions in the distribution models of African wild silk moths (Gonometa species, Lasiocampidae) using different representations of modelled host tree distributions

Biotic interactions influence species niches and may thus shape distributions. Nevertheless, species distribution modelling has traditionally relied exclusively on environmental factors to predict species distributions, while biotic interactions have only seldom been incorporated into models. This study tested the ability of incorporating biotic interactions, in the form of host plant distributions, to increase model performance for two host‐dependent lepidopterans of economic interest, namely the African silk moth species, Gonometa postica and Gonometa rufobrunnea (Lasiocampidae). Both species are dependent on a small number of host tree species for the completion of their life cycle. We thus expected the host plant distribution to be an important predictor of Gonometa distributions. Model performance of a species distribution model trained only on abiotic predictors was compared to four species distribution models that additionally incorporated biotic interactions in the form of four different representations of host plant distributions as predictors. We found that incorporating the moth–host plant interactions improved G. rufobrunnea model performance for all representations of host plant distribution, while for G. postica model performance only improved for one representation of host plant distribution. The best performing representation of host plant distribution differed for the two Gonometa species. While these results suggest that incorporating biotic interactions into species distribution models can improve model performance, there is inconsistency in which representation of the host tree distribution best improves predictions. Therefore, the ability of biotic interactions to improve species distribution models may be context‐specific, even for species which have obligatory interactions with other organisms.The University of Pretoria (RDP funding to Michelle Greve), the South African National Research Foundation and the South African National Biodiversity Institute.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1442-99932018-12-01hj2018Plant Production and Soil Scienc

Empty Gonometa postica cocoons function as nest sites and shelters for arboreal ants

Arboreal ants use a variety of plant structures as nesting sites, but may also nest in structures created by arboreal ecosystem engineers. We observed, for the first time, ants using empty cocoons of the economically important silk moth species, Gonometa postica, as shelter and nesting sites. Individual trees and individual cocoons were occupied predominantly by one dominant ant species, although in some cases by co-occurring ant species. Ant abundance and occurrence were positively related to cocoon size and the presence of scale insects on branches of the trees, and negatively influenced by cocoon occupancy by other invertebrates. Ants also preferred cocoons containing only small parasite holes as opposed to cocoons containing large moth emergence holes, suggesting that ants select cocoons based on cocoon characteristics. Further, these results reveal that other arboreal invertebrates appear to benefit from cocoon production. Empty cocoons could be functioning as nest sites and shelters for arboreal invertebrates, and they could create favourable habitats for other invertebrates on Vachellia erioloba. Therefore, G. postica acts as an autogenic ecosystem engineer and current silk harvesting practices, which partly rely on harvesting empty G. postica cocoons, may have potential local and large-scale implications for inter-specific interactions in these arboreal systems.The University of Pretoria (RDP funding to Michelle Greve), the South African National Research Foundation (grant number: 101515) and the South African National Biodiversity Institute.http://www.elsevier.com/locate/jaridenv2018-09-30hj2017Plant Production and Soil ScienceZoology and Entomolog