The effects of development, vegetation-type conversion, and fire on low-elevation Southern California spider assemblages

California sage scrub (CSS), a native ecosystem type of low-elevation areas of Southern California, is increasingly threatened by urban development, altered fire regimes, and vegetation-type conversion to non-native grasslands. Using pitfall traps, we examined how suburbanization, type conversion, and fire influence ground-dwelling spider assemblages in eastern Los Angeles County, CA, by surveying spiders in three habitats (CSS, non-native grasslands, and suburban areas) before and after a fire that occurred in a small portion of our study site. Spider assemblages in the suburban habitat differed from those in CSS and non-native grassland habitats, but CSS and grassland assemblages did not significantly differ. This suggests that the urban development, but not vegetation-type conversion to non-native grasslands, has significant effects on ground-dwelling spider assemblages. Fire had no observable effect on assemblages. Because ground-dwelling spiders were not impacted by fire and type conversion, increased fire frequencies, which often result in the establishment of non-native grasses, may not deleteriously influence this animal group, a differing pattern from other taxonomic groups. However, the rapid urban development occurring in low-elevation areas of Southern California means that species requiring nonsuburban sites for their survival (15 species, 24.1%) may be threatened and require conservation assessment.