Yllenus

Abstract: A long-term diet analysis of a polyphagous jumping spider Yllenus arenarius Menge 1868 (13 yr, n = 321 prey items) was carried out in Central Poland. Due to the spider's long life cycle two cohorts are present for the whole season and for one month three cohorts coexist, which allowed me to investigate whether coexisting spiders feed on similar or different prey. Diets of spiders from these three cohorts were found to differ in three aspects: prey taxa, prey diversity and prey size. Spiders from each cohort maintained a fairly constant ratio between prey size and their own size throughout the life cycle, which resulted in dietary separation between individuals from coexisting cohorts. Such mechanisms may reduce the intensity of competitive interactions between coexisting spiders.

Abstract: We examined differences in predatory behavior between two age groups (newly hatched spiders vs. spiders over 12 weeks old) of Yllenus arenarius Menge 1868 (Araneae: Salticidae). The spiders hunted three prey taxa (leafhoppers, caterpillars and thrips) for which they possess pre-programmed predatory behavior. The aim of the study was to check the influence of age and experience on pre-programmed predatory behavior and predatory success. Age-dependent changes occurred in four aspects of predation: direction of approach, mode of approach, distance of attack and predatory success.

Abstract: Decisions made by predators during predatory encounters are often based on multiple factors that may influence the outcome of the encounters. For stalking predators their visibility to the prey and the ability of their prey to escape may be important factors influencing predatory success. Hence they are likely to adapt their predatory behavior when approaching prey on backgrounds with different camouflaging properties, but only if the prey is able to escape. To test whether jumping spiders flexibly adapt their predatory behavior to camouflaging properties of the background and prey type, the behavior of Yllenus arenarius (Araneae, Salticide), a cryptically colored jumping spider hunting leafhoppers (high escape potential) and caterpillars (low escape potential) on two types of background: matching and non-matching for the spiders was analyzed. Background color had a significant effect on the spiders’ jumping distance and their predatory success, but only if the prey had a high escape potential. No differences occurred between backgrounds if the prey could not escape. On camouflaging background the spiders attacked leafhoppers from a shorter distance and had a higher success than on non-camouflaging background.