Variações estruturais ligadas à fenologia em plantas de Eryngium: consequências para as comunidades de aranhas

Abstract

This study presents the structural resources represented by the spatial structures of Eryngium pandanifolium (gravatás) plants and by the trophic resources, represented by the availability of food for the subsequent trophic levels. The objective of this study is to analyze the effect of morphological variation of Eryngium pandanifolium on spider communities that use this plant as a resource. The experiments and sampling took place during the months of November 2019 and February 2020, the study area is located in a field of the Pampa biome. The choice of plants sampled was carried out in a systematic way along linear transects, totaling 240 samples of individuals E. pandanifolium and another 30 samples of shrub vegetation and 30 of undergrowth vegetation. All spiders that occupied the plant were sampled and they were classified according to their stage of development, sex and foraging guild. During the study, a series of samplings was carried out under natural conditions and under experimental conditions in the field, the combination of data from different experimental treatments allowed to evaluate the contribution of different factors on the abundance of spiders associated with plants. The data obtained were organized into sampling blocks: (1) long-term effects of habitat complexity on spiders; (2) short-term effects of habitat complexity on spiders; (3) time effect on the spiders' occupation dynamics; (4) effect of trophic subsidy promoted by inflorescences; (5) on the complementarity of the assemblage of spiders in the gravatás in relation to the surroundings. The results were: (1) the abundance of weaver spiders was independent, in relation to cursorial spiders, it was possible to visualize a decrease in the number of spiders at the base of the plants throughout the development of the inflorescence; (2) in plants in which the associated spiders were previously removed, the abundances of weaver spiders as well as the abundance of cursorial spiders were found to be independent of the variation in system complexity; (3) the abundance of weaver spiders is independent of the time of colonization of plants with similar structural complexities, cursorial spiders revealed a negative relationship throughout the sampling period; (4) the presence of the inflorescences had no effect on the abundance of spiders at the base, regardless of the foraging guild, the effect was noticeable on the abundance of cursorial spiders in the inflorescences; (5) the abundance of weaver spiders was similar between the experimental groups, while cursorial spiders were more abundant in E. pandanifolium than in the surroundings. 509 spiders were found on the gravatás and 100 spiders on the other plants, totaling 15 families and 39 morphospecies. Spider foraging guilds showed different responses to the structural complexity of the study system. Weaving spiders presented relationships independent of the structural complexity or trophic subsidy of the ties in all sampling blocks. The increase in structural complexity had an effect on cursor spiders in almost all sampling blocks, except for the second block.