Abundance, coexistence and behavioural interactions among juveniles of two sympatric tarantulas from Argentina

Grammostola vachoni (Schiapelli & Gerschman, 1961) and Plesiopelma longisternale (Schiapelli & Gerschman, 1942) are two sympatric tarantula species living in mountain systems from central Argentina occurring at the same microhabitat. Adults and juveniles of both species live under rocks, where they construct their shelters. They are also synchronous in egg sac laying and hatching of the first stages (December and January). Given this scenario, it is probable that juveniles compete for resources, such as shelters during early stages. Thus, we evaluated the abundance and demography of both species at their natural habitat, by registering the sizes of individuals found, their refuges, and percentage of coexistence. We also conducted intra- and interspecific interactions to register the behavioural patterns of spiders against congeners and hetero-specific individuals. Grammostola vachoni was more abundant at one site studied; however, both species showed similar abundances at the second site. We identified 16 behavioural units. The most frequent behaviour displayed by both species was “retreat”. The most frequent behaviour during interspecific interactions was “retreat” for P. longisternale, whereas for G. vachoni it was “abdomen elevation”. For intraspecific encounters, the most common behaviours were “contraction” and “silk deposition” for P. longisternale, while for G. vachoni they were “retreat”, “raising palps”, and “grasp”.