Unexpected high diversity of galling insects in the Amazonian upper canopy: The savanna out there

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 vegetation habitats, hygrothermically stressed environments with temperature at lethal limits and high levels of leaf sclerophylly. © 2014 Julião et al

Insetos galhadores associados a duas espécies de plantas invasoras de áreas urbanas e peri-urbanas Galling insects associated with two species of ruderal plants in urban and peri urban areas

Os insetos têm sido considerados importantes indicadores de mudanças ambientais e da qualidade de habitats. Apesar de seu hábito séssil, fácil visualização, abundância, e especificidade de hospedeiro, insetos indutores de galhas não têm sido utilizados em estudos desta natureza. Neste estudo foi investigado o uso potencial de insetos galhadores associados a duas espécies de plantas hospedeiras ruderais (Baccharis dracunculifolia e Vernonia polyanthes: Asteraceae) como bioindicadores da qualidade de habitats. Procurou-se responder às seguintes questões: (i) A diversidade de insetos galhadores é afetada pelo tipo de uso e ocupação da paisagem (solo)?; (ii) A resposta das comunidades de insetos galhadores difere entre as duas espécies de plantas hospedeiras?; (iii) A diversidade de insetos galhadores é influenciada por características bióticas e físicas dos biótopo urbanos? Foram coletadas 6.226 galhas, pertinentes a 6 espécies de insetos galhadores associados à V. polyanthes e 11 espécies associadas à B. dracunculifolia. Não foi encontrada nenhuma diferença na riqueza de insetos galhadores entre os biótopos amostrados. No entanto, a abundância de insetos galhadores apresentou diferenças significativas quanto ao tipo de uso e ocupação da paisagem. As galhas foram mais numerosas em biótopos menos urbanizados, sendo observado uma relação forte e positiva com a porcentagem de cobertura vegetal do biótopo. As comunidades de insetos galhadores de ambas as espécies de plantas hospedeiras apresentaram respostas diferenciais quanto ao tipo de uso da paisagem. Os resultados sugerem três fatores que podem estar envolvidos com a diversidade de insetos galhadores em áreas urbanas: (i) estrutura dos habitats num biótopo; (ii) abundância e distribuição espacial do recurso planta hospedeira e; (iii) freqüência e intensidade do manejo de reservas, parques, jardins e terrenos baldios de uma dada área urbana. Constatou-se ainda que áreas verdes em espaços urbanos são de fundamental importância na manutenção da diversidade de insetos.<br>Insects have been considered as important bioindicators of environmental changes and habitat quality. In spite of its sessile habit, easy localization, abundance and host specificity, insects that induce galls have not been utilized in studies of this nature. It was investigated the suitability of gall-inducing insects associated to two ruderal host plant species (Baccharis dracunculifolia and Vernonia polyanthes: Asteraceae) as bioindicators of habitat quality. The following questions were addressed: (i) is gall-inducing insect diversity influenced by different types of land use?; (ii) are the responses of galling insect communities different between host plants?; (iii) how does the biotic and physical features of the biotope influence the gall-inducing insect diversity? It was found 6,226 galls, belonging to six galling insect species on V. polyanthes and 11 galling species on B. dracunculifolia. No difference was found in galling species richness among land use types. Nevertheless, gall-forming insect abundance was statistically different among the biotopes studied. Insect galls were more numerous in biotopes with lower urbanization levels. Gall abundance showed a strong and positive relationship with the percentage of vegetal cover. Gall-forming insect communities on both host species showed differential responses to the different land use types. The results suggest that three factors may be involved with galling insect diversity in urban areas: (i) habitat structure in the biotope; (ii) resource abundance (host plant abundance and distribution); and (iii) frequency and intensity of management in reserves, parks, city squares, wastelands found at a given urban area

A Venn diagram representing the number of galling morphospecies exclusive and common to the <i>terra firme</i> (blue), <i>várzea</i> (green), and <i>igapó</i> (orange) forests, Central Amazonia, Brazil.

<p>Presence/absence data revealed great dissimilarity among Amazonian forest types, even considering the flooded forests.</p

GIR in Central Amazon sites and values from other vegetations types from Brazil and world.

<p>The figure was re-drawn from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114986#pone-0114986-g002" target="_blank">Fig. 2</a>, page 586, work of Price <i>et al.</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114986#pone.0114986-Price1" target="_blank">[3]</a>. GIR (galling insect richness) is equivalent to the number of galling species <i>per</i> sample point.</p

Relationship between galling insect abundance (GIA) and number of tree species sampled (TSS) in the <i>terra firme</i> (red curve and symbols), <i>várzea</i> (green curve and symbols), and <i>igapó</i> (black curve and symbols) forests at Amazon.

<p>All parameters were significant in our initial model, in spite of its insufficient predictive power.</p

Mechanisms shaping the distribution patterns of galling insects in the Amazonian forests.

<p>Down arrow icon means lower value/level; up arrow icon, higher ones in the comparison between canopy and understory.</p

Ratios between galling insect richness and number of tree species sampled (GIR/TSS) in the understory (U) and canopy (C) of different vegetation types in several biogeographic regions.

<p>*Our Study.</p><p>Ratios between galling insect richness and number of tree species sampled (GIR/TSS) in the understory (U) and canopy (C) of different vegetation types in several biogeographic regions.</p

Number of individuals and species of host plants; galling insect richness (GIR), abundance (GIA), and dissimilarity among the <i>terra firme</i>, <i>várzea,</i> and <i>igapó</i> forests in Amazon, Brazil.

<p>*N: number of sampling sites in each landscape.</p><p>Number of individuals and species of host plants; galling insect richness (GIR), abundance (GIA), and dissimilarity among the <i>terra firme</i>, <i>várzea,</i> and <i>igapó</i> forests in Amazon, Brazil.</p

Study area at the BDFFP, MSDR, and ASDR reserves, Central Amazonia, Brazil.

<p>Map sources: <a href="http://www.pdbff.inpa.gov.br/area3p.htm" target="_blank">http://www.pdbff.inpa.gov.br/area3p.htm</a> (Biological Dynamics of Forest Fragments Project - BDFFP); <a href="http://www.mamiraua.org.br/downloads/mapas" target="_blank">http://www.mamiraua.org.br/downloads/mapas</a> [Mamirauá (MSDR) and Amanã (ASDR) Sustainable Development Reserves].</p