Comparing Spider Sampling Methods in a Eucalypt Forest in Wet and Dry Conditions

Environmental variability, such as fluctuations in rainfall, can strongly influence spider population dynamics and assemblage composition. The study examined whether rainfall in the preceding three months, i.e., wet or dry conditions, using three different methods in the same sites within a eucalyptus forest, influenced the overall species and abundance of spiders captured and thus how wet or dry conditions influenced the overall spider assemblage and community structure. In south-east Queensland, Australia, rainfall is highly variable throughout the year and does not conform to distinct wet or dry seasons; therefore, "wet" and "dry" classifications in this study refer specifically to preceding rainfall conditions rather than seasonal categories. Sampling was conducted during dry conditions (75 mL of rain in the three months preceding collection) and during wet conditions (300 mL of rain in the three months preceding collection) to assess overall differences in spider richness, diversity and assemblage composition between wet and dry conditions by combining data from the three sampling methods. Species richness was significantly higher in dry conditions compared to the wet conditions. Diversity indices indicated that the more common spider species remained consistent between wet and dry conditions. Ordination analyses revealed changes between wet and dry conditions, primarily driven by fluctuations with less common spider species, rather than community changes at the family level. For vibration-based collections of spiders, only 30.5% of species overlapped between wet and dry conditions, whereas family-level overlap was 75%, indicating rainfall-driven changes occurred primarily at the species level rather than at the family level. Spider abundance was consistently higher under dry conditions across all methods. In vibration-based collections, 90% of species was collected within 60 min. However, using this method, species appeared more slowly under wet conditions, suggesting that rainfall may influence spider responses to vibrational stimuli. Survey method strongly influenced species richness with night hand collection of spiders resulting in the greatest number of species observed. Spider species richness and diversity collected using the vibration-based method were similar in wet and dry conditions and between sites. This supports the reliability of this method for sampling spiders that respond to vibrations and should be used complementarily with other survey methods.