Caracterização fitossociológica da vegetação lenhosa e diversidade, abundância e variação sazonal de visitantes florais em um fragmento de caatinga no Semiárido Paraibano.

Abstract

Caatinga biome presents different facies and local floristic composition, and the knowledge of the fauna and flora that characterizes the different facies becomes urgent due to the high anthropogenic pressure. Pollinators play a vital ecological role, participating in the process of fertilization of plants, and studies about the whole guild of floral visitors in local communities of caatinga are still absent. The objectives of this study were: a) perform the phytosociological characterization of the woody component of a caatinga fragment with relatively homogeneous phisiognomy, describing its floristic composition and structure, b) study the diversity, abundance and seasonal variation of floral visitors in a caatinga unit of landscape in semiarid of Paraiba. The study was conducted in Santa Terezinha (7°01'S, 37°24'W), Paraiba State, Brazil. For the phytosociological characterization, we sampled all shrub-tree individuals, alive or dead, still foot, with a circumference of 30 cm from the base ≥ 10 cm and total height ≥ 1 m, were included. Ten plots of 20 x 20 m, randomly distributed. 649 specimens (603 alive and 46 dead) comprising 21 species in 21 genera and 11 botanical families were sampled. The average density was estimated at 1622.5 individuals/ha and basal area at 9.21 m2/ha. The main species, as the index of importance value were Poincianella pyramidalis (Tul.) L. P. Queiroz, Aspidosperma pyrifolium Mart. and Commiphora leptophloeos (Mart.) J. B. Gillett. Despite being an well preserved area within the region, it has a high density of plant individuals with small diameter stems ≤ 6 cm (63%) and seems to be still regenerating. The floristic composition and species richness are similar to those found in other studied areas of the region, especially the abundance of Commiphora leptophloeos and Amburana cearensis (Allemão) A.C. Sm. The guild of floral visitors was systematically sampled with entomological nets or direct observation of individuals in flower or in flight, along six transects. Data collection was carried out during one year, a day per month, from 5:30 to 16:30, with an hour break every hour of sampling. The sampled guild of floral visitors is composed of four groups of insects and a bird. A total of 1393 individuals representing 143 species were recorded. Hymenoptera, Lepidoptera and Diptera were the orders with the greatest number of species. However the order Lepidoptera were the most abundant, followed by Hymenoptera and Diptera. Apis mellifera L. (Hymenoptera) and Eurema elathea Cramer (Lepidoptera) were the predominant species. Thirty-eight plant species were visited by anthophilous during the study period, representing twenty plant families, the most visited: Convolvulaceae, Lamiaceae, Fabaceae, Malvaceae and Euphorbiaceae. The rainy season had had a higher number of species and individuals, while 88% of the species and 80% of the individuals were recorded. The three main orders of visitors showed a significant decrease in abundance after the start of the dry season, but species were recorded with active adults during the dry season, including flies, butterflies and solitary bees. The higher species richness and abundance were sampled in the interval between 7h30 and 8h30, with some species