How pervasive is biotic homogenization in human-modified tropical forest landscapes?

Abstract Land-cover change and ecosystem degradation may lead to biotic homogenization, yet our understanding of this phenomenon over large spatial scales and different biotic groups remains weak. We used a multi-taxa dataset from 335 sites and 36 heterogeneous landscapes in the Brazilian Amazon to examine the potential for landscape-scale processes to modulate the cumulative effects of local disturbances. Biotic homogenization was high in production areas but much less in disturbed and regenerating forests, where high levels of among-site and among-landscape b-diversity appeared to attenuate species loss at larger scales. We found consistently high levels of b-diversity among landscapes for all land cover classes, providing support for landscape-scale divergence in species composition. Our findings support concerns that b-diversity has been underestimated as a driver of biodiversity change and underscore the importance of maintaining a distributed network of reserves, including remaining areas of undisturbed primary forest, but also disturbed and regenerating forests, to conserve regional biota

Ant-nest distribution in a remnant of tropical rainforest in southeastern Brazil

Ant communities are generally extremely interactive, and competition between ant species seems to be widespread. This characteristic of ant communities tends to produce a uniform pattern of nest distribution. In this study, we aimed to test the nest distribution pattern, putting forward hypotheses to explain the pattern. Nest mapping was carried out by delimiting ten one-square-meter quadrats, randomly located in a remnant of tropical rainforest in Viçosa, Brazil. In each quadrat, the nests were surveyed in the litter and surface soil up to 3 cm deep. A total of 295 nests from 41 ant species were collected in the ten quadrats. The pattern of nest distribution in the whole forest was aggregated, while the species showed a random distribution. The pattern of nest distribution inside each quadrat was also aggregated. The presence of species, such as Brachymyrmex sp.1 and Hypoponera sp.4 , with high nest densities suggests the occurrence of nest budding. This may be the reason for the aggregated nest distribution. Another explanation for this apparent aggregation is species specialization in a patchily distributed habitat. The results suggest that competition is not an important process in the regulation of soil and litter ants distribution and, consequently, in the regulation of species richness in the studied area

Edge and shape effects on ant (Hymenoptera: Formicidae) species richness and composition in forest fragments

In this paper, we tested four hypotheses relative to edge and shape effects on ant communities: (i) forest edges have lower species richness than the remnant core; (ii) species richness increases with distance from the edge; (iii) irregularly shaped remnants have lower species richness than more regular remnants; (iv) there is a higher similarity of species composition between edge and core in irregular than in regular remnants. We sampled litter ant communities on the edge and core of ten remnants, in Viçosa, Minas Gerais, Brazil. Species richness was larger at the forest core than at the edges, although did not increase with distance from the edge. Species richness did not vary with shape complexity. The similarity of species composition between edge and core showed a decreasing trend with remnant area, and did not vary with shape complexity. The observed differences of species richness between forest core and edge may be due to higher harshness of edges, caused by environmental changes. The absence of relationship between species richness and distance from the edge might indicate the range of edge effects, which would be smaller than the smallest distance of core sampled. Therefore, edges would affect litter-dwelling ant species richness in a distance smaller than 50 m. The observation of species composition allowed us to notice an effect of fragmentation that would not be noticed if we were considering only species richness. Edge may serve as step to generalist species, which may use it to colonise forest remnants. Furthermore, small remnants are more colonisation-prone by such species, and have a more homogeneous species composition than large remnants

Ant community composition and its relationship with phytophysiognomies in a Brazilian Restinga

In this study, the composition of ant communities was compared in four adjacent phytophysiognomies in Morro dos Conventos Restinga, Brazil. We tested our hypothesis that the ant community composition differs between habitats across a gradient from sea to inland continent. Ant species were sampled with pitfall traps. Overall, 71 ant species were collected. Ant species composition differed between phytophysiognomies. Our results suggest that environments were more similar in the adjacent than in the more distant phytophysiognomies, a pattern similar to the vegetation zonation and gradient sea–inland Restinga. Thirteen species determined more than 50% of the dissimilarity between phytophysiognomies. Solenopsis saevissima was the species that contributed more to ant species composition distinction between phytophysiognomies, followed by Pheidole and Camponotus species. The type of vegetation is one of the main factors affecting the composition of ant communities in Restinga. The role of plants is linked to the availability of resources and conditions and they may determine ant assemblage composition and different interactions occurring in Restinga

Foraging behavior of bee pollinators on the tropical weed Triumfetta semitriloba: flight distance and directionality

We studied flight distance and directionality of bee pollinators on the tropical shrub weed Triumfetta semitriloba Jacq. (Tiliaceae), addressing (1) within- and between-plant movement pattern; (2) distances flown between plants; (3) flight directionality. Flowering plants were distributed in well-delimited clumps, in each of two pasture areas (A1 and A2) and one area of forest gap (A3), in Viçosa, southeastern Brazil. Five solitary bee species, Augochlorella michaelis, Augochloropsis cupreola, Pseudocentron paulistana, Ceratinula sp., Melissodes sexcincta, and two social bee, Plebeia droryana, P. cf. nigriceps were observed. All species moved mainly to the nearest flower on the same individual plant and, in between-plant movements, to the first or second nearest neighbor. All species moved non-randomly, presenting a flight directionality in departures (maintenance of flight direction), but with a high frequency of turn angles. It is suggested that this foraging behavior pattern occurred because of the resource quantity and quality (pollen or nectar), and environmental characteristics such as flower density and resource distribution.Estudamos a distância de vôo e a direcionalidade de abelhas polinizadoras da planta invasora Triumfetta semitriloba Jacq. (Tiliaceae), sobre os seguintes aspectos: (1) padrão de movimentação dentro e entre plantas; (2) distância de vôo entre plantas; (3) direcionalidade de vôo. As plantas floridas eram distribuídas em manchas bem delimitadas, em duas áreas de pasto (A1 e A2) e uma área de clareira de mata (A3), em Viçosa, MG, Sudeste do Brasil. Foram observadas cinco espécies de abelhas solitárias, Augochlorella michaelis, Augochloropsis cupreola, Pseudocentron paulistana, Ceratinula sp., Melissodes sexcincta e duas espécies sociais, Plebeia droryana, P. cf. nigriceps. Todas as espécies moveram principalmente para a flor mais próxima, dentro da mesma planta e, nos movimentos entre plantas, para o primeiro ou segundo vizinho mais próximo. Todas as espécies apresentaram uma direcionalidade no padrão de vôo, ou seja, uma movimentação não aleatória, mas com uma alta freqüência de ângulos laterais. Sugere-se que esse padrão de comportamento de forrageamento ocorreu devido à qualidade e quantidade de recurso (pólen ou néctar) e às características ambientais como a densidade de flores e distribuição do recurso nas manchas