Scholarly Commons

Socially-Facilitated Antipredator Responses in the Wolf Spider Pardosa milvina

Animals use diverse sources of information to assess predation risk. Many may use direct information such as visual or odor cues associated with a predator. Additionally, social species may use indirect sources of information such as observing antipredator responses of nearby conspecifics even when they themselves have no direct information about risk. The relative value and interaction of direct predator cues and indirect social information about predation risk is unclear, particularly when these sources provide conflicting information. The wolf spider, Pardosa milvina, displays effective antipredator behavior (freezing) when detecting silk from adults of another co-occurring wolf spider, Tigrosa helluo. Pardosa also occurs at high densities in agricultural fields where encounters with Tigrosa vary spatially and temporally. We tested how Pardosa antipredator responses varied when detecting Tigrosa silk cues directly compared to social cues from conspecifics with or without access to predator silk. Using an automated digital tracking system, we measured activity of Pardosa under six different social and predator cue conditions including variations of when the subject does or does not have access to predator cues directly, and/or is able to observe conspecifics with or without access to these same predator cues. We found spiders walked significantly less in the presence of direct predator cues independent of social cues, however mean speed of movement and freezing responses were both significantly influenced by both direct predator cues and social cues. When nearby conspecifics had access to predator silk but the subject did not, the subject increased antipredator responses. When the subject had direct exposure to predator silk cues but nearby subjects did not, the subject reduced antipredator responses. Although Pardosa mediate some defensive behavior based on social cues, direct information about a predator generally had a stronger effect on antipredator behavior. Our results suggest that behaviors of nearby conspecifics can influence the intensity and prevalence of antipredator behaviors of this spider in complex ways.