ABSTRACT
Abstract The fauna of Euglossini bees is poorly known in savanna regions, making it difficult to understand how these bees use open vegetation environments. The aim of this study was to evaluate the influence of landscape structure on species abundance and composition of Euglossini bees in naturally heterogeneous savanna landscapes. Nine sites were sampled monthly using six traps with chemical baits. Three aromatic essences (eucalyptol, methyl salicylate and vanillin) were used to attract the Euglossini. Surrounding environmental conditions were measured using three independent variables, calculated in multiple scales: index of local vegetation and two landscape indices (Shannon Diversity and area-weighted shape). We compared the competing hypotheses through model selection based on Second-order Akaike Information Criterion (AICc). The four competing hypothesis were: (1) The local vegetation complexity favors Euglossini bees species richness and/or abundance (local vegetation hypothesis); (2) The proportion of the native vegetation types favors Euglossini bees species richness and/or abundance (habitat amount hypothesis); (3) Higher landscape diversity shall increase species richness of Euglossini bees (landscape heterogeneity hypothesis); (4) More complex landscape configuration shall favor the Euglossini bees richness and/or abundance (landscape heterogeneity hypothesis). We sampled 647 individuals belonging to six species of two distinct genera. Our results support the habitat amount hypothesis since bees’ abundance was strongly related with the proportion of habitat in the surrounding landscape. This may be related to the availability of floral and nesting resources in some types of savanna vegetation.
Resumo A fauna das abelhas da tribo Euglossini é pouco conhecida em regiões de savana, tornando difícil a compreensão de como essas abelhas usam ambientes com vegetação aberta. O objetivo desse estudo foi avaliar a influência da estrutura da paisagem na abundância e composição de espécies de abelhas Euglossini em paisagens naturalmente heterogêneas de savana. Nove locais foram amostrados mensalmente utilizando seis armadilhas com iscas químicas. As essências eucaliptol, salicilato de metila e vanilina foram utilizadas para atrair os machos de Euglossini. As condições ambientais foram medidas usando três variáveis, calculadas em múltiplas escalas: índice de vegetação local e dois índices de paisagem (diversidade de Shannon e o índice de forma ponderado pela área). Através da seleção de modelos baseada no critério de informação de Akaike de segunda ordem (AICc) comparamos as hipóteses alternativas: (1) Vegetação local mais complexa favorece as abelhas Euglossini (hipótese da vegetação local); (2) A proporção dos tipos de vegetação nativas favorece as abelhas Euglossini (hipótese da quantidade habitat); (3) A diversidade da paisagem favorece a riqueza de espécies de abelhas Euglossini (hipótese da heterogeneidade da paisagem); (4) Configuração mais complexa da paisagem favorece a riqueza e/ou abundância de abelhas Euglossini (hipótese da heterogeneidade paisagem). Nós amostramos 647 indivíduos pertencentes a seis espécies de dois gêneros distintos. Nossos resultados apoiam a hipótese de quantidade de habitat já que a abundância das abelhas foi fortemente relacionada com a proporção de habitat nas paisagens circundantes. Esses resultados podem estar relacionados com a disponibilidade de recursos florais e substratos para nidificação em alguns tipos de savana.
ABSTRACT
The tropical forest fragmentation is known to affect the spatial structure of the landscape and habitat. These alterations can modify the attributes of bat assemblages, however, this phenomenon has been little studied and understood. In this work we evaluated the structure of landscape (i.e. composition and configuration) and vegetation, and its relationship with assemblage- and population-level characteristics of phyllostomid bats in a tropical rainforest of Southeastern Mexico. For this, we previously selected 12 sites located in continuous and fragmented forests, where bats were captured using mist nets during a two years sampling effort (144 nights). Bats relative abundance, species richness (diversity of order 0, 0D), Shannon diversity index (¹D) and Simpson index (²D) were evaluated in all sites, and their relationship with seven measures of landscape structure and seven measures of vegetation structure was described using a Hierarchical Partitioning Analysis. A total of 1 840 individuals of 29 species of phyllostomid bats were captured in this period. Differences in the assemblages were manifested only in the relative abundance and not in the richness of the species. The assemblages of fragmented forest exhibited greater variation in species composition and a greater abundance of frugivorous and nectarivorous bats in comparison with the assemblages of continuous forest. The landscape configuration was related to the assemblage- and population-level attributes, contrasting with previous studies where the composition was a key element. At habitat level, tree density and canopy cover determined the abundance of bats. Nectarivorous and frugivorous bats were mostly found in disturbed vegetation landscapes, primarily due to landscape configuration (e.g. edge density). This phenomenon could be a response to the availability of food in primary and intermediate successional stages, which are characterized by an abun-dance of food value.
La fragmentación de bisques tropicales altera la estructura especial del paisaje y del habitat . Estas alteraciones pueden modificar los atributos de las agregaciones de murciélagos, sin embargo este fenómeno ha sido poco estudiado y comprendido. Se evaluó la estructura del paisaje (i.e. composición y configuración) y vegetación, y sus relaciones con características a nivel de agregación (ensamble) y población de murciélagos filostómidos en una selva tropical del sureste de México. Se encontró que las modificaciones en las agregaciones solo se manifiestan en la abundancia relativa y no en la riqueza de especies. La configuración del paisaje fue un elemento relacionado con los atributos a nivel de ensamble y de población, contrastando con estudios previos donde la composición fue un elemento clave. A nivel de hábitat se encontró que la densidad arbórea y cobertura del dosel determinan la abundancia de murciélagos. Los murciélagos nectarívoros y frugívoros prefieren paisajes con vegetación alterada y están relacionados principalmente con la configuración del paisaje. Este fenómeno podría ser una respuesta a la disponibilidad de alimento en ambientes sucesionales primarios e intermedios, que se caracterizan por una alta proliferación de plantas con potencial alimenticio.