Micro-habitat distribution among web-building spiders: implications for community and food web structure

Web-building spiders are abundant natural enemies whose ecology is of central importance to the function of arthropod communities in agroecosystems. Recent work suggests that these spiders can fill an important role in conservation biological control, but before such programs can be adopted, an understanding of the factors that impact the feeding ecology of linyphiid spiders must be investigated. One important factor impacting the diet of spiders is the selection of web sites, which influences the spider’s exposure to, and success in capturing, prey. Here, web-placement data collected in the field are presented for three species of linyphiid spider (Tennesseellum formicum, Erigone autumnalis and Grammonota inornata) and one species of tetragnathid (Glenognatha foxi) inhabiting alfalfa fields. Height of the web and usage of attachment structures varied by species, such that each species inhabited a unique spatial niche. Such micro-habitat differentiation can be a means of trophic specialization because the diet of sedentary spiders is primarily determined by prey availability in the micro-habitat. Analysis of sticky trap catches using a pair-wise design revealed a significant correlation between height above the ground and activity density of Collembola, one of the most important prey taxa for linyphiid spiders. Molecular gut-content analysis using Collembola-specific DNA primers revealed trophic niche separation between spiders building webs at different heights. These data indicate that diet and micro-habitat are closely linked for web-building spiders, and justify efforts to implement conservation biological control through manipulations of habitat structure.