Watching your friends get eaten: bystander effects on predator recognition and subsequent survival in the wolf spider Pardosa milvina
Observational learning by witnessing predation of conspecifics can be important for predator recognition and subsequent survival yet studies of this phenomenon among arthropods are lacking. We manipulated predator experiences of the wolf spider, Pardosa milvina and then placed the spiders in open arenas with the larger co-occurring predatory wolf spider, Trochosa ruricola to test for differences in defensive behavior and survival based on prior predator experiences. We set up five treatments (N = 140, n = 23-35/treatment): 1) Pardosa that observed a conspecific for 1 h, 2) Pardosa that observed the predator, Trochosa ruricola for 1 h, 3) Pardosa that observed the predator Trochosa ruricola consume a conspecific during a 1 h period, 4) Pardosa that observed a conspecific evade predation by Trochosa for 1 h., and 5) Pardosa in an empty container (control). We then placed individual Pardosa in 20 cm d. arenas with a live Trochosa for 1 h and recorded predation latency, time spent moving, the number of lunges by the predator, and the number of evasive hops by Pardosa. We found no significant difference in the number or rate of evasive hops, time spent moving in the arena, or the number or rate of lunge responses by Trochosa across treatments; however, we did find significantly higher predation and shorter predation latency for the control treatment and Pardosa that witnessed Trochosa consume a conspecific relative to all other treatments. Our results suggest that prior predator experiences can influence subsequent survival of Pardosa and that witnessing predation of conspecifics can significantly increase predation risk.