Does niche partitioning explain spider richness in vacant lots?

Ecologic theory specifies that bottom-up, species-level interactions, such as competition, are main drivers of arthropod community abundance and richness. It does not address complex landscape-level pressures that may be important drivers of species richness in urban areas. Cleveland, Ohio has gained greenspace through the creation of vacant lots, which are minimally managed and vary in the degree of habitat fragmentation. To understand the mechanisms that influence urban spider abundance and richness, we tested the hypothesis that increased mowing frequency and landscape scale urbanization intensity will reduce prey availability and increase competition among sheet web spiders (Linyphiidae), which would result in fewer Linyphiidae species occupying a vacant lot patch. In 2014, we established a network of 7 vacant lots in two treatments: control (mowed monthly, n = 4) and meadow (mowed biannually, n = 3). Within these sites we collected three focal competitors and extracted DNA from the gut of each spider. Prey was identified to family level using PCR amplified with a universal primer and bioinformatic analyses. Abundance and species richness of Linyphiidae spiders was gathered from pitfall traps in the same year. We found that lot management did not impact niche partitioning, nor did the degree of niche partitioning predict community richness or abundance. Instead, as imperviousness increased, so did spider abundance, breadth and overlap. This indicates that greenspaces surrounded by more imperviousness have a concentration of prey and spiders. Therefore, landscape context is a strong driver of insect habitat use, which should inform city-wide conservation planning.