Diversidade, abundância e sazonalidade de visitantes florais diurnos em área de caatinga e floresta ciliar no Semiárido Paraibano, Nordeste do Brasil.

Abstract

Floral visitors are potential pollinators of flowering plants that contribute to the maintenance of biological diversity. In the semiarid region of northeastern Brazil, they face a long dry period, and may be distributed unevenly between different environments. The objective of this work is to compare the diversity, abundance and seasonality of diurnal floral visitors between areas of xerophilous scrub (caatinga) and riparian forest in the semiarid region of Paraíba. The guild of flower visitors was studied by means of standardized samples of individuals on flowers or in flight, along six transects in each habitat, captured by a single collector with an entomological net. From February 2011 to January 2012 the floral visitors were sampled monthly, during one day from 5:30am to 16:30pm, with a 1 hour break after every hour of sampling, totaling 72 hours/collector of sampling effort for each area. The faunal composition of floral visitors was represented by five groups of animals, one group of birds and four of insect. A total of 1427 and 3293 individuals and 100 and 65 species were recorded for the caatinga area and riparian forest, respectively. The order Lepidoptera was the most representative in species richness in both areas. The order Hymenoptera was the most abundant in the caatinga while Lepidoptera, in riparian forest. Both areas presented a large number of accidental and rare species of flower visitors and two species, Apis mellifera and the Eurema elathea, were eudominant. The Shannon diversity indices between areas were statistically different (t = -3.589, p = <0.01). This difference is primarily due to the greater number of species, once the evenness was similar to the studied areas. The estimation of species richness of flower visitors including species not sampled (Chao 1), allowed us to recognize that we collected about 65% of the species, considering the two areas together. Each monthly sample area near riparian forest tended to have more species and individuals than the same sample undertaken in the caatinga. In the rainy season, the richness and abundance of floral visitors were higher, with 95% of the species being in caatinga and 90% for the riparian forest, especially the month of February with 29 and 42 species, respectively. In the sample of rainy season more species and individuals were collected than in the dry season (Wilcoxon, p = <0.01). For Lepidoptera and Hymenoptera there was a greater diversity and abundance during the rainy season in both areas, but for Diptera it was not observed a great diversity in the rainy season in the caatinga, possibly related to greater dependence of this group on mesic environments. Regarding butterflies, with a sampling effort of 72 net/hours, 47 species were recorded, with 28 in caatinga and 42 in the riparian forest, comprised of five families and 13 subfamilies. The Hesperiidae and Nymphalidae families were the most representative in number of species, representing together 57% in caatinga and 67% in riparian vegetation, respectively. When comparing the number of individuals, the Pieridae family was the most abundance, representing 54% and 69% in each of the areas, respectively. The Sorensen index of similarity between areas was 1.76, higher than that observed for all of the pollinators (0.6078). Each monthly sample in the area near riparian forest tended to show a greater number of species (n= 12, z= 2.4318, p= 0.0150) and individuals (n= 12, z= 2.5103, p= 0, 0121). The botanical families that received the highest number of records were Malvaceae, Asteraceae and Convolvulaceae (54% of total visits), especially the species Sida galheirensis and Centratherum punctatum in Caatinga, and Asteraceae and Rubiaceae (64% of total visits together), specially the species Richardia grandiflora and Tridax procumbens in the area near the riparian forest. The highest species richness and abundance of floral visitors in the area near the riparian forest is interpreted as evidence of the role of refuge for many species that live in the semiarid region, however, more detailed studies are needed to verify its role for each species in particular.