Plant species richness, not hygrothermal stress, is the main predictor of gall-inducing insect richness in Peruvian Amazon forests

Patterns of gall-inducing insect diversity tend to be influenced by both habitat-related and plant-related characteristics. We investigated the distribution patterns of galling insects in four vegetation types (terra firme forest, white-sand dry forest, white-sand wet forest and palm swamp forest) of the Peruvian Amazon to test if the insect gall diversity (1) differs among different types of vegetation and (2) depends on host plant richness. In total, we found 11,579 galls belonging to 249 insect gall morphotypes, distributed across 30 botanical families and 75 plant species. Among host plant families, Fabaceae showed the greatest richness of insect gall morphotypes. We found that galling species richness was lower in palm swamp forest than in white-sand forests, which can be explained by the lower richness of plants in this type of vegetation. However, we found no evidence of greater richness in xeric habitats (e.g., white-sand dry forest) than in more mesic vegetation (terra firme forest), contradicting the hypothesis of hygrothermal stress. We also found that plant species richness was positively influenced with the richness and abundance of galling species, regardless of vegetation type. Galling insect species composition differed significantly between vegetation types, similarly to the floristic composition. Our findings show that the diversity of galling insects in the tropical rainforests of Peruvian Amazon are mainly influenced by host plant composition and host plant richness.Abstract in Spanish is available with online material. Los patrones de diversidad de insectos inductores de agallas tienden a estar influenciados tanto por caracteristicas relacionadas con el habitat y las plantas. Investigamos los patrones de distribucion de insectos inductores de agallas en cuatro tipos de vegetacion (bosque de tierra firme, bosque seco de arena blanca, bosque humedo de arena blanca y bosque de pantano de palmas) de la Amazonia peruana para evaluar si la diversidad de insectos inductores de agallas (1) difiere entre diferentes tipos de vegetacion y (2) depende de la riqueza de las plantas hospederas. En total, encontramos 11,579 agallas pertenecientes a 249 morfotipos de insectos inductores de agallas, distribuidos en 30 familias botanicas y 75 especies de plantas. Entre las familias de plantas hospederas, Fabaceae mostro la mayor riqueza de morfotipos de insectos inductores de agallas. Encontramos que la riqueza de especies inductoras de agallas era menor en el bosque de pantano de palmas que en los bosques de arena blanca, lo cual puede explicarse por la menor riqueza de plantas en este tipo de vegetacion. Sin embargo, no encontramos evidencia de una mayor riqueza en habitats xericos (por ejemplo, bosque seco de arena blanca) que en vegetacion mas mesica (bosque de tierra firme), contradiciendo la hipotesis del estres higrotermal. Tambien encontramos que la riqueza de especies de plantas fue positivamente influenciada por la riqueza y abundancia de especies inductoras de agallas, independientemente del tipo de vegetacion. La composicion de especies de insectos inductores de agallas diferia significativamente entre los tipos de vegetacion, de manera similar a la composicion floristica. Nuestros hallazgos muestran que la diversidad de insectos inductores de agallas en los bosques tropicales de la Amazonia peruana esta principalmente influenciada por la composicion y la riqueza de las plantas hospederas. We found that galling species richness was lower in palm swamp forests than in white-sand forests, which can be explained by the lower richness of plants in this type of vegetation. However, we found no evidence of greater richness in xeric habitats (e.g., white-sand dry forest) than in more mesic vegetation (terra firme forest), contradicting the hypothesis of hygrothermal stress. Moreover, plant species richness was positively influenced by the richness and abundance of galling species. Galling insect species composition differed significantly between vegetation types, similar to the floristic composition.image