Abstract
A relatively large number of studies reassert the strong relationship between galling insect diversity and extreme hydric and thermal status in some habitats, and an overall pattern of a greater number of galling species in the understory of scleromorphic vegetation. We compared galling insect diversity in the forest canopy and its relationship with tree richness among upland terra firme, várzea, and igapó floodplains in Amazonia, Brazil. The soils of these forest types have highly different hydric and nutritional status. Overall, we examined the upper layer of 1,091 tree crowns. Galling species richness and abundance were higher in terra firme forests compared to várzea and igapó forests. GLM-ANCOVA models revealed that the number of tree species sampled in each forest type was determinant in the gall-forming insect diversity. The ratio between galling insect richness and number of tree species sampled (GIR/TSS ratio) was higher in the terra firme forest and in seasonally flooded igapó, while the várzea presented the lowest GIR/TSS ratio. In this study, we recorded unprecedented values of galling species diversity and abundance per sampling point. The GIR/TSS ratio from várzea was approximately 2.5 times higher than the highest value of this ratio ever reported in the literature. Based on this fact, we ascertained that várzea and igapó floodplain forests (with lower GIA and GIR), together with the speciose terra firme galling community emerge as the gall diversity apex landscape among all biogeographic regions already investigated. Contrary to expectation, our results also support the “harsh environment hypothesis”, and unveil the Amazonian upper canopy as similar to Mediterranean vegetation habitats, hygrothermically stressed environments with leaf temperature at lethal limits and high levels of leaf sclerophylly.
Highlights
In spite of the increasing knowledge on the spatial distribution patterns of many species worldwide, the evolutionary processes and ecological mechanisms shaping them remain poorly known, due to geographic and physiological limitations
Only part of the dataset was included in our statistical analysis in order to balance sampling efforts at different forest types (S1 Table)
Higher abundance and richness of galling insects were found in the terra firme forest, followed by varzea and igapohabitats (Table 1)
Summary
In spite of the increasing knowledge on the spatial distribution patterns of many species worldwide, the evolutionary processes and ecological mechanisms shaping them remain poorly known, due to geographic and physiological limitations. A relatively large number of studies reassert the strong relationship between galling insect diversity and hydric, thermal, and nutritional stresses in some habitats, resulting in an overall pattern of a greater number of galling species [3, 12,13,14,15,16] This endophytic insect fauna would benefit from the protection against desiccation, sunlight radiation, and natural enemies (free-living herbivores, predators, fungi, other pathogens) in these habitats, and by nutritive tissues provided by gall structure [8]. Few studies have been developed in the Neotropical vegetation with non- scleromorphic physiognomy ([18], but see [19, 20])
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