Tri-trophic networks of oak gall-inducing-insects and their parasitoids in Mexican avocado agrosystems: Forest coverage and local climatic variables importance

Abstract

Despite trees of temperate forest ecosystems (TFEs) maintain a great diversity of biotic interactions, they are threatened by changes in land use. In Mexico, the main threat to TFEs is the conversion to avocado orchards, generating forest fragmentation affecting trophic networks, like gall-inducing insects (GII) and their parasitoids. We determined the changes in structure and diversity of trophic assemblages of GII and their parasitoids associated in Quercus castanea, Q. obtusata and Q. magnolifolia, as well as the plant vigor roll on GII diversity in sites with different percentages of forest and avocado orchards in Mexico. Per study site, we selected 20 trees with gall presence for each oak species. Also, we assessed climatic variables effects on plant vigor and GII diversity. We found that plant vigor traits and GII diversity for all oak species increases as avocado orchard does. Contrary, a decrease of parasitoid diversity was detected for areas with greater avocado orchard cover. GII diversity had a positive relationship with temperature, but negatively with precipitation in all study sites. Tri-trophic networks differed among sites, having lower connectance and greater modularity in sites with higher avocado orchard cover, while in sites with higher forest cover was the most connected and diverse. Our results suggest that TFEs conversion to avocado orchards increases plant vigor and GII diversity, but decreases parasitoid diversity and modifications in trophic networks. Therefore, we highlight the need to conserve and manage forest remnants in the avocado belt because they preserve and maintain a great diversity of biotic interactions.