Within mixed-species assemblages, closely related species may face interspecific competition and reproductive interference. Species may evolve adaptations to outcompete or coexist—alternatively, assemblages may also exist in a non-equilibrium state between the two extremes. Understanding the dynamics between syntopic species requires careful studies conducted at a fine spatial resolution, an especially important for small invertebrate animals. We characterized interspecific interactions within a mixed-species assemblage consisting of four species of Habronattus jumping spiders, a genus commonly found in syntopic assemblages where males are known to indiscriminately court conspecific and heterospecific females alike. Through detailed focal observations, we evaluated species overlaps in space use, temporal occurrence, light habitat preference, and behavior, including courtship. We assessed whether observed heterospecific interactions occurred more frequently than random chance by comparing the observed data to network reference models. Our findings revealed interspecific overlap across all evaluated variables, which may indicate shared environmental requirements amongst the species and potential interspecific competition. However, there was a slight temporal shift between H. calcaratus and H. coecatus, while H. decorus showed some divergence in space use and light habitat preference that may be associated with its distinct courtship display. Additionally, we observed sex differences in activity levels across all species that could represent a selection for male ‘scramble competition’ strategy. Lastly, heterospecific behavioral interactions were frequently observed, including heterospecific courtship. However, compared to our reference models, heterospecific interactions in this assemblage occurred less often than random chance. Altogether, our findings suggest that species in this assemblage are engaged in some level of interspecific competition and reproductive interference but may be evolving mechanisms to mitigate these pressures. This study, therefore, establishes an ecological foundation for future investigations into possible adaptive responses such as species recognition, reproductive character displacement, and behavioral niche differentiation.

We conducted focal observations of individual spiders over two field seasons. Spatial data were collected by first creating a local reference map and second measuring spider locations to landmarks on the local reference map. Behavioral interactions were summarized at networks, which was then compared to a reference network model to see whether the observed data have more heterospecific interactions than compared to chance.