Aspectos da ecologia populacional e comportamental de Nephila clavipes (Linnaeus, 1767) (Araneae, Nephilidae)

Abstract

Nephila clavipes (Linnaeus, 1767) is a species of orb-web spider found throughout Brazil. The aim of this work was to evaluate aspects of the populational ecology of the species, along with growth, development, and phenology of individuals located in the campus of the Universidade Federal de Juiz de Fora (UFJF), in the municipality of Juiz de Fora, Minas Gerais. Approximately 100 webs (solitary and aggregate) were observed during the years 2008 and 2009. Both males and females were stained on the dorsal region of the opisthosoma with several colors of enamel paint. The rainy season comprised the largest number of individuals in the population, both for females and for males. The curve of the number of female variation was proportional to the semelparous species curve. In the second year of sampling, the population was basically composed of immigrants, since the original female population dispersed from the sample area in the first weeks of observation. In order to analyze the behavioral aspects of the species, it was evaluated the ability of females in occupying webs of conspecifics, and described the behaviors performed during the territorial disputes. Three field manipulation experiments were carried out; two experiments in previously vacant webs: one of them, with the reintroduction of a spider in their own web (n=30); the other, with the introduction of a spider in a vacant web (n=30). The third experiment, was performed with the introduction of a spider in a previously occupied web (n=55). The experiments showed that both resident spiders and introduced spiders remained in the webs in which they were placed. Resident females demonstrated that, when they were bigger, they showed an advantage in the dispute against the invasive species, though it was not noticed any significant advantage when the invasive individuals had the same size or were bigger. The resident invested more in the maintenance of the web than the invasive, performing more agonistic behaviors and returning more times to the web after combats. It did not occur intolerance among individuals on the support wires, thus indicating that the formation of aggregations might be related to the tolerance of individuals to accept the presence of conspecifics from nearby areas.