Web‐Site Tenure in the Long‐Jawed Spider: Is It Risk‐Sensitive Foraging, or Conspecific Interactions?

Long—jawed spiders (Tetragnatha elongata) present a paradox to behavioral ecologists, because spiders in prey—rich habitats move to new web sites almost every night, while those in poor habitats rebuild their webs on precisely the same spot for many nights in a row. Caraco and Gillespie built a risk—sensitive foraging model to explain this paradox. Their model demonstrates that it may be advantageous to relocate more often when experiencing high prey capture rates (under certain regimes of spatiotemporal heterogeneity). However, their model had not been tested. I tested the Caraco—Gillespie model by conducting food additions experiments in the field with spiders in the poor habitat. The results do not support the model. A reexamination of the Caraco–Gillespie model suggests that it implicitly assumes unlikely larger scale patterns in prey availability. I present an alternative hypothesis to explain the paradox. Since conspecific density is higher in rich habitats, I propose that more intense conspecific interactions in rich habitats cause these spiders to move to new web sites more often. I conducted the replicates of a density reduction experiment in a rich habitat, and the results support the conspecific density hypothesis. The results of these experiments challenge a widely cited example of risk—sensitive foraging, and underline the importance of explicitly considering multiple scales of variation in ecology.