18ª JORNADAS DEL GRUPO IBÉRICO DE ARACNOLOGÍA         Top-down control of Lycosa hispanica on decomposition of leaf litter mixtures from a semiarid ecosystem of SE Iberian Peninsula           Miguel Prado López1, Francisco I. Pugnaire1, & Jordi Moya Laraño1*           1 Departmento de Ecología Funcional y Evolutiva, Estación Experimental de Zonas Áridas - CSIC, Carretera de Sacramento s/n, 04120-Almería, España     * jordi@eeza.csic.es           Soil predators can affect litter decomposition via top-down cascading effects going through the soil animal community (in terms of abundance and/or composition) down to the litter. Litter mixtures, in turn, can regulate the rate at which soil fauna communities affect decomposition (bottom-up control). However, to date we do not know whether the presence of predator differently influence ecosystem functions such as decomposition, when exposed to low vs. high litter diversity (i.e., mixtures). In other words, we do not know how top-down and bottom-up control of decomposition interact to determine net decomposition rates. This is important in an scenario of global change in which biodiversity, and especially top predator, are threatened. Using a laboratory experiment our work assesses the cascade effects of wolf spiders (Lycosa hispanica) on decomposition rates of 3-species litter mixtures (Stipa tenaccisima, Chamaerops humilis and Retama sphaerocarpa), through their direct predatory or threatening effect on isopods (Porcellio ornatus). Against expectations and despite evidence that isopods were heavily fed upon by wolf spiders, we found that regardless of litter diversity or identity, treatment with spiders and/or spider cues had higher rates of litter decomposition, probably because isopods were attracted to spider excreta and prey remains, which are food sources to them.