The role of habitat complexity on spider communities in native alpine grasslands of New Zealand

1. Physical structure and species composition of vegetation determine spider diversity through habitat availability. Here, we assess, for the first time, the role of plant structure on spider communities in New Zealand native alpine tussock grasslands. We investigate the specific associations between spider assemblages and plant communities and test the hypothesis that spider diversity increases with plant diversity and tussock cover. 2. Spiders were sampled using density- and abundance-activity-dependent methods. Data on physical characteristics and species composition of plants revealed gradients in vegetation, driven by distinct intra-ecosystem plant communities. Effects of vegetation on spider diversity and composition were assessed through linear mixed-effects models. Redundancy analysis was used to determine and visualise the spider species–level response to gradients in plant compositions. 3. There was a positive relationship between plant diversity and spider diversity, while the effects of tussock cover varied with spider taxa. Overall, physical structure and species composition of vegetation had effects on the abundance of a similar number of spider species and families. 4. Gradients in vegetation were matched to gradients in spider communities, whose diversity and composition varied according to their habitat preference. The family Orsolobidae was associated with wetland vegetation, and Linyphiidae with shrubs. The abundance of certain spider families and species, such as Lycosidae and Anoteropsis hilaris, was consistently affected by vegetation. 5. Environmental factors, such as soil moisture, may affect plant species composition and physical structure in tussock grasslands, which in turn determine spider assemblages. Lycosidae were identified as potential indicators of structural changes in tussock grassland plants and could be valuable for ecological monitoring in conservation management.