Ecology and life history of Meta bourneti (Araneae: Tetragnathidae) from Monte Albo (Sardinia, Italy)

The orb-weaver spider Meta bourneti Simon 1922 (Araneae: Tetragnathidae) is one of the most common cave predators occurring in the Mediterranean basin. Although the congeneric M. menardi represented the model species in several studies, our knowledge of M. bourneti is only founded on observations performed on a handful of populations. In this study M. bourneti spiders were studied in caves of Monte Albo (Sardinia, Italy) over a year. Generalized Linear Mixed Models were used to analyze spider occupancy inside cave environments, as well as spider abundance. Analyses on M. bourneti occupancy and abundance were also repeated for adults and juveniles separately. Generalized Linear Models, were used to weight species absence based on its detection probability. Linear Mixed Models were used to detect possible divergences in subterranean spatial use between adult and juvenile spiders. Although widespread on the mountain, M. bourneti generally showed low density and low detection probability. Most of the individuals observed were juveniles. The spiders generally occupied cave sectors with high ceilings that were deep enough to show particular microclimatic features. Adults tended to occupy less illuminated areas than juveniles, while the latter were more frequently found in sectors showing high humidity. The abundance of M. bourneti was strongly related to high humidity and the presence of two troglophile species, Hydromantes flavus Wake, Salvador & Alonso-Zarazaga, 2005 (Amphibia: Caudata) and Oxychilus oppressus (Shuttleworth, 1877) (Gastropoda: Panpulmonata). The abundance of juveniles was related to sector temperature and humidity, the presence of H. flavus and O. oppressus and to morphological sector features. However, when only adults were considered, no significant relationships were found. Adult and juvenile spiders did not differ in their spatial distribution inside the caves studied, but a seasonal distribution of the species along cave walls was observed. Microclimate was one of the most important features affecting both the presence and abundance of M. bourneti in subterranean environments. Individuals tended to occupy lower heights during hot seasons.