Padrão de atividade, mudanças no uso de substrato e efeitos da chuva diurna na atividade noturna de Phoneutria reidyi (Araneae: Ctenidae) na Amazônia Central

Abstract

The wandering spiders are models for the understanding of the ecology of predators, but the knowledge of their ecology is still based on few species, mostly from temperate regions. The occurrence of rain is common in humid tropical forests, but their influence on the wandering spiders behavior is virtually unknown and there are few studies on the intraspecific coexistence in species where cannibalism may be an important interaction. During 16 months i made 19 trips to get data on activity pattern, use of substrates, diet and effect of rainfall on the nocturnal activity of wandering spider Phoneutria reidyi (Ctenidae) in a coconut plantation in the municipality of Rio Preto da Eva, and 30 more days of data collection of these spiders in the forest fragment of the campus of Federal University of Amazonas in Manaus, to check the effect of rainfall in the activity of spiders in "terra firme". The censuses of spiders were held in two time intervals at night, early evening (19:00 - 23:59h) and late night (01:00 - 04:00h), and i obtained data on the use of substrate and diet spiders of different stages of development. To check the effect of rain on the behavior of spiders, we compared the number of active spiders in 30 pairs of subsequent nights, each pair with one night after a daytime rain and another without daytime rain. There was a reduction in the activity of spiders at the end of the night period, however, we found no evidence of temporal segregation between different sizes of individuals, indicating that small spiders are not foraging at different times to avoid competition for resources or cannibalism by spiders larger. However, we found a strong shift in the use of foraging substrate and diet of these spiders in the final phase of its development. We suggest that the cause in the difference on the use of foraging substrate is that the smaller spiders avoid palms to reduce the probability of cannibalism in this population where the density of this species is high. There was a strong reduction in nocturnal activity of spiders in days with daytime rains in both areas studied (plantation and forest). We discuss the causes and consequences of the powers of diurnal rainfall on the spider behavior and the need to take this into count in ecological studies with bases in visual surveys and pitfall traps. This study helped to show that the change in the use of foraging substrates can help reduce intraspecific predation P. reidyi and to show the importance of rain on the behavior of this species, which belongs to one of the spider genera of higher medical interest the world, and whose ecology is still poorly known.