Seasonal Variation in Whole-Body Elemental Concentrations and Excreta Production of a Riparian Orb-Weaving Spider...

Predators influence nutrient cycling by assimilating elements from their prey and returning nutrients to ecosystems via excretion and discarded prey remains. However, seasonal variation in the contribution of predators to nutrient cycling remains poorly understood, particularly for terrestrial arthropod predators such as spiders. We examined temporal variation in whole-body elemental concentrations, excreta C and N concentrations, and cumulative excreta output in a riparian orb-weaving spider (Larinioides cornutus) across the growing season of 2024. Adult females were collected across seven sampling periods spanning mid-June to early October, and whole-body concentrations of macronutrients (carbon [C], nitrogen [N], phosphorus [P]) and multiple trace elements were quantified. Whole-body N and P concentrations, and several trace elements (potassium [K], lithium [Li], manganese [Mn], sodium [Na], nickel [Ni], sulfur [S], silicon [Si], and strontium [Sr]) exhibited significant seasonal variation, with elements differing in both the direction and shape of temporal patterns. Cumulative excreta production also varied significantly across the season and exhibited a mid-season peak, whereas excreta C and N concentrations remained comparatively stable. Model selection favored linear relationships for most responses, although quadratic models were supported for some variables (i.e., spider body mass, excreta production, K concentrations, and Na concentrations), indicating non-monotonic seasonal dynamics. These findings suggest that seasonal shifts in prey availability and/or spider physiology influence nutrient assimilation and excreta production in riparian spiders. Our results highlight the importance of incorporating both trace elements and seasonal context when evaluating predator-mediated nutrient cycling in terrestrial ecosystems.