Species Composition and Assemblage Structure of Terrestrial Isopods (Crustacea: Isopoda: Oniscidea) in Olive Groves of the Atacama Desert, Chile

Dryland agroecosystems can sustain soil arthropod communities, yet their detritivore faunas remain poorly documented in hyperarid regions. Terrestrial isopods (Crustacea: Isopoda: Oniscidea) are important macrodetritivores whose assemblages in northern Chile remain largely unknown. Using standardized pitfall trapping, we characterized the isopod assemblage of five olive (Olea europaea) groves differing in age, structure, and irrigation in the Huasco Valley, southern Atacama Desert. We collected 14,128 individuals belonging to four oniscidean taxa in three families: Armadillidium vulgare, Porcellio laevis, Porcellionides cf. sexfasciatus, and Benthanoides sp. The first three are introduced Palearctic species, whereas Benthanoides is a native Neotropical genus. Together, Benthanoides sp. and P. laevis accounted for 91.3% of captures. Observed taxon richness differed by only one taxon among groves, whereas total activity-density varied nearly 20-fold and dominance structure differed markedly. Benthanoides sp. dominated the young grove and P. laevis the intermediate grove, while the two centennial groves supported the most balanced assemblages. Overall, native and introduced taxa contributed almost equally to total captures (46.7% and 53.3%, respectively). Because grove age, structure, and irrigation covary, and each combination of characteristics was represented by only one or two groves, these among-grove patterns should be interpreted descriptively. These findings provide the first taxonomically resolved baseline for Oniscidea in Atacama olive agroecosystems and show that cultivated groves can support a native detritivore at high activity-density alongside introduced synanthropes.