Ecosystem engineering by mud wasps: influence of the environment and nest structure.

Many organisms act as environmental engineers by modifying the physical structure of their habitats and altering the availability of resources for other organisms. Mud wasps are known for building mud nests for their offspring, which are abandoned once the larvae complete metamorphosis and emerge as adults. Here, we compare the role of the mud wasps as ecosystem engineers in two different environments and analyze the influence of nest structure on the community of tenants in Veracruz, México. We sampled for abandoned nests (with at least one emergence opening) in human constructions and in a nearby forest area (medium subdeciduous tropical forest) measuring: their volume, number and diameter of openings, and the presence of tenants. Of the 88 sampled mud nests, 43% had tenants, totaling 234 individuals from 12 orders and 29 morphospecies. Spiders and ants were the most species-rich groups, while psocids were the most abundant tenants. We found a significant and positive effect of nest volume and number of openings on tenant species richness and abundance, whereas neither the diameter of the openings nor the environment had any effect. Our work provides evidence of mud wasps acting as ecosystem engineers, in both urban and forest environments, creating new spaces that other organisms can use as shelters. We also conclude that nest volume and the number of openings are important factors influencing the secondary use of these constructions. Moreover, these results suggest that the presence of nests and their non-removal from human constructions may be useful for the conservation of small organism communities in anthropized environments.