Temperature and tree number drive tree crown-dwelling arthropod diversity in Brazilian semi-arid cities

Urbanisation is one of the most severe land use changes with significant negative impacts on several biological groups. However, the response of arthropods to this process is still unclear, especially in cities located in arid regions, which represent an important part of global urban ecosystems. Here, we examined variations in abundance, richness, diversity and taxonomic composition of the tree crown-dwelling arthropods in 10 Brazilian cities of semiarid climate located in the dry forest region (Caatinga), taking into account temperature gradients and number of street trees along the cities. We expected that cooler (in a hot range of temperature) and more forested cities would present richer, more abundant and distinct communities than warmer cities. This hypothesis is supported by the large amount of evidence showing the negative effects of temperature on the local structuring of biological communities. We used the method of the arboreal arthropod collector to sample the arthropod community inhabiting trees crowns up to 10 m in height. We collected a total of 22,911 arthropod specimens belonging to two classes (Insecta and Arachnida) and 24 orders. As expected, temperature (min 21.7 degrees C, max 26.8 degrees C) proved to be a significant predictor of arthropod diversity in semiarid cities. Cities with higher temperatures reduce taxonomic unit richness (0D) by 33% and diversity (1D and 2D) in up to 75% and affect composition of arthropod orders composition. On the other hand, the effect of tree numbers showed distinct responses among the sampled orders, positively contributing to the abundance of Psocoptera, while exerting a negative effect on the abundance of Thysanoptera. Overall, our findings highlight the importance of temperature and number of trees in determining urban arthropod fauna.