Understory host plant and insect gall diversity changes across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest

Abstract

Topographic gradients in terra firme forests are associated with pronounced changes in soil texture, soil nutrients and distance to the water-table, thereby creating different hydric and nutritional conditions for plants and their associated herbivore community. The aim of this study was to investigate galling species and host plant richness and gall species composition across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest. Nineteen 250 x 3 m plots were randomly sampled in the valley, slope, plateau-slope transition, and plateau habitats in terra firme forests. All individual dicotyledonous plants 1 to 3 meters high were examined for the presence of insect galls. Galling species and host plant richness differed significantly among the studied habitats and were higher in slope habitats (drier habitats), as expected. More humid areas (valleys) showed the lowest richness of galling species, and a lower number of understory host plants. PERMANOVA and PERMDISP results demonstrated that the gall species composition differed significantly in the valley, slope, plateau-slope transition, and plateau areas. However, these structural differences in species composition could be due to unequal dispersion of variability among forest habitats. Our data suggested that spatial heterogeneity, such as a mosaic of local water status and nutrient availability resulting from the topographic conditions, can affect host plants and their associated galling insects. KEYWORDS: habitat stress, soil nutrients, species diversity, terra firme forest, topographic gradient Riqueza de insetos galhadores associados a habitats de sub-bosque com diferentes topografias e níveis de estresse hídrico e nutricional em uma floresta da Amazônia Central, Brasil RESUMOAs variações topográficas encontradas nas florestas de terra firme são acompanhadas por fortes mudanças no conteúdo de argila e concentração de nutrientes do solo, criando, portanto, diferentes condições hídricas e nutricionais para plantas e as comunidades de herbívoros associadas. O objetivo do presente estudo foi avaliar a riqueza e composição de espécies de insetos galhadores e suas plantas hospedeiras ao longo de um gradiente topográfico com habitats que diferem quanto ao estresse hídrico e nutricional. Dezenove parcelas de 250 x 3 m foram estabelecidos aleatoriamente em habitats de vertente, platô, transição platô-vertente e baixio, claramente distintos em áreas de terra firme. Todas as dicotiledôneas com 1 a 3 metros de altura foram examinadas quanto à presença de galhas de insetos. As galhas encontradas foram coletadas e insetos galhadores foram classificados em morfoespécies. A riqueza de galhadores e de plantas hospedeiras diferiram significativamente entre os habitats estudados, e como esperado, foi maior no habitat de vertente. As áreas mais úmidas (baixios) apresentaram menor riqueza de plantas hospedeiras no sub-bosque e, conseqüentemente, um número menor de espécies de galhadores. Os resultados das análises de PERMANOVA e P...

Fire affects galling insect communities through vegetation changes in a subtropical seasonally semiarid forest

“…As we expected, species composition of galling insects was coupled with that of vegetation communities and significantly different among the three fire scenarios. This result agrees with previous studies indicating different species composition of galling insects under different fire scenarios (Bakhshandeh-Savadroodbari et al, 2017;Cronin et al, 2020) and different floristic composition (Araújo et al, 2013;Julião et al, 2017;Melo Júnior et al, 2019;Mendonça Junior, 2007;Veldtman & McGeoch, 2003). In addition, in agreement with Knuff et al (2019), we statistically corroborated the strong correspondence between species compositions of vegetation and galling insect communities.…”

“…Some studies have considered only the host plant richness and a linear positive relationship between host plant and galling insect richness was also found (Araújo, 2011;Souza et al, 2016). Moreover, in agreement with the high specificity of galling insects to their host plants (Carneiro et al, 2009), the specific composition of these insect communities has been closely related to floristic composition (Julião et al, 2017;Knuff et al, 2019). The proportion of plants damaged by phytophagous insects was also used as an herbivory indicator (Ekholm et al, 2019;Faeth & Simberloff, 1981) and showed changes in disturbed habitats (Altamirano et al, 2016).…”

Assessing invertebrate herbivory in human‐modified tropical forest canopies

“…There is some evidence that herbivory patterns seem to vary between understorey studies and our canopy research. For example, studies in Western Amazonia found that between 0.6% and 10% of all sampled individuals of seedlings and understorey trees presented galls (Julião et al, 2017;Vasconcelos, 1999), while we found galling to be present in 83% of our stems. In the same region, the incidence of miners and chewers was found in 1.5% and 73% of understorey trees, respectively (Vasconcelos, 1999).…”

“…Across the Amazon, herbivory levels present a great variation between seedlings and understorey trees; while incidence is much less reported, severity ranges from 1% until 50% of leaf area loss (Benitez-Malvido et al, 1999;Darrigo et al, 2018;Julião et al, 2017;Massad et al, 2013;Metcalfe et al, 2014;Poorter et al, 2004;Vasconcelos, 1999). Our results are toward the low end of the severity range, with an average 6.7% of leaf area loss by chewers.…”

“…Our results are toward the low end of the severity range, with an average 6.7% of leaf area loss by chewers. This large variation in herbivory levels both within and between studies can be due to a number of factors, including plot altitude and topography (Julião et al, 2017;Metcalfe et al, 2014), as well as humandriven disturbances to the system (Massad et al, 2013). But one of the most likely and important sources of variation is related to the different methods used to assess herbivory incidence and severity.…”