Suchergebnisse

In order to understand the effects of human impacts on structure and functioning of tropical forests, we should consider studies on animal-plant interactions such as antplant mutualistic interactions.We investigated the mutualistic interactions between ants (Azteca genera) and Cecropia plants in habitats of secondary forest and pasture used as cattle fields. We tested for the following hyphothesis: (i) Cecropia from pasture are more susceptible to foliar herbivory than the Cecropia from the forest, and (ii) the defense promoted by ants of Azteca genus is less efficient in the pasture when compared to the forested areas. We selected four areas inserted in Atlantic rain forest domain surrounded by secondary forest and by cattle pastures. The herbivory was more intense in the pasture than in the secondary forest. The presence of Azteca species diminished foliar herbivory only in the forested areas, where we observed a significant increase in herbivory after the removal of A. alfari colony. We argue that the greater herbivory in pasture occurs probably due the lack of other plant resource, being Cecropia paschystachya Trécul and C. glaziovii Snethl., isolated in a "sea of grass" without connection with other tree vegetation, opposite scenario observed in forested habitats. The defense of Azteca only in the secondary forest, leading us to suppose that: 1) not even the your aggressive behavior is able to reduce the intense herbivory in the pasture; 2) the your behavioral pattern in forest is not the same in deforested environments and / or 3) mutualism may be undergoing changes due to abiotic effects on pasture.

Natural earth mounds in many ecosystems harbor higher biodiversity than surroundings because they provide greater habitat heterogeniety. However, in the semi-arid Caatinga ecosystem of NE Brazil, natural mounds have much less vegetation and leaf litter with lower biodiversity as compared to the surrounding lowlands. The following hypotheses were tested: (i) low vegetation cover on the mounds results from highly compacted and leached soils as compared to adjacent lowlands and (ii) low vegetation cover reduce ant populations and diversity because of limited foraging and nesting resources. This study was carried out in four mound fields. Adjacent lowlands were found to have twice as many ant individuals as the mounds along with higher ant species richness and diversity. The high resistance of the mound soil to root penetration and low pH could be the main reason for the difference in diversity between mound and adjacent lowlands. Further investigations are needed to infer whether this low diversity on mounds is a natural feature, or a result of ongoing environmental degradation in the Caatinga, whereupon deforestation leads to hardened and compacted soils.

This study aims to analyze how the vegetation structure (physiognomy) and seasonal changes between seasons (wet and dry) influence richness, diversity and composition of ant species of arboreal and shrubby Caatinga environments. The vegetation structure was significantly different among the three strata for all parameters (mean diameter of vegetation, level of herbaceous cover, degree of coverage and thickness of litter and percentage of canopy cover). We collected 127 ant species. The mean number of species was approximately two times higher in the rainy season than in the dry season. There was no difference in species richness between the arboreal and shrubby Caatinga physiognomies nor interaction between season and physiognomy. Despite the similarity in richness, species composition differed between physiognomies, however we found no difference in composition between seasons. The seasonal differentiation may be mainly related to the variation in the overall numbers of individuals circulating in the environment, since the enhancement of resource availability during rainy season allows the colony to grow or expand foraging activities, which increases local diversity. Water restriction explains the limited diversity in both environments, while the occurrence of species with greater resource specificity may determine differences in ant composition. Differences in composition of each of Caatinga's physiognomy enhance beta diversity, therefore, raising the overall diversity in the Caatinga Domain.

This study evaluates the richness and composition of the epigeic ant fauna in two Caatinga areas (site 1: Brejo Novo and 2: Frizuba) within a transitional region (between the Caatinga and the Decidual Atlantic Forest) in the Municipality of Jequié, state of Bahia, Brazil. Ants were sampled using pitfall traps and Winkler extractor method in 50 randomly chosen points, totalizing a sampling area of 12.5 ha per site. Overall, we identified 60 species belongingto 27 genera. The most speciose genera were Pheidole, Camponotus, and Solenopsis (with five species each) followed by Wasmannia and Cephalotes (four species each). Pheidole sp1. was the most frequent species (occurring in approximately 60% of the samples). Since site 1 did not possess a litter layer (and therefore could not be sampled by the Winkler extractor) comparisons between the two areas were made using only the data provided by the pitfalltrap method. The Simpson diversity indexes calculated for sites 1 and 2 were 0.87 and 0.89, respectively, and showed no statistically significant differences (p ≤ 0.417). The Jaccard coefficient revealed only 35.5% similarity in species composition between the two areas. The results suggest that the presence of litter contributed to increased species richness (the Winkler method added 28 species in the sum total of species collected) and "shaped" a distinct faunal composition of the area. The present study is the first ant fauna inventory in the region and reveals an unexplored conservation potential for the Decidual Forest and the Caatinga of northeastern Brazil.