Amplitude de nicho trófico em Tidarren haemorrhoidale (Araneae, Theridiidae): determinantes comportamentais e implicações nutricionais sobre parâmetros de história de vida

Abstract

We investigated different aspects related to the foraging and feeding of the Tidarren haemorrhoidale spider (Bertkau, 1880) as the possible segregation of trophic niches involving another sympatric species, the possibility of individual specialization within the population, the behavioral routines used to capture different prey, role of previous experiments for foraging efficiency and how different diets affect the fecundity and survival of individuals. In order to perform this work, the spiders were observed in their natural environment and were also subjected to controlled feeding experiments and filmed in the laboratory. Tidarren haemorrhoidale builds webs in the same environment as Nihonhimea tesselata, but these species segregate their niches, capturing distinct prey. We could observe marked differences in the position and architecture of the webs that possibly are related to the interception of different types of insects. In addition, we observed that no individual specialization occurred in any of the studied species, with individual niches not differing from the population niche. We could also observe that the variation in the diet of the individuals can not be explained by the spatial differential distribution of the resources, since closer individuals do not present greater overlap in their diets. In relation to the foraging behavior, we could conclude that T. haemorrhoidale needs more time to perform the ant trapping routines compared to beetles. This result is due to the caution necessary to immobilize the ants that present risks of injury to the predator. The behavioral routines for capture were similar between preys, with only differences in the time required to complete parts of these routines. Previous experiences was not a determinant of a higher capture efficiency (manipulation time) for T. haemorrhoidale, since individuals did not decrease capture times after successive interactions with the same prey type. Finally, diet-related issues may be very important in the life history of T. haemorrhoidale. Our results confirm the existence of different effects on the maintenance of weight and fecundity according to the type of prey consumed. Although a mixed diet can guarantee good results in weight maintenance and egg production, we have shown that monotypic diets can also satisfy the nutritional needs of the species.