Multiple predator effects and habitat complexity alter an intraguild predation module in pond communities

Background/Question/Methods

Intraguild predation (IGP) and multiple predator effects (MPE) each can have a large effect on population dynamics, community structure and ecosystem function. These two factors are not mutually exclusive, however, as the outcomes of IGP and MPEs are often interrelated processes.  Furthermore, environmental variables often interact with both of these processes, such that the outcome of IGP and MPE vary under different abiotic constraints.  Increased habitat complexity is one factor that has been shown to influence both IGP and MPE, as it can provide refuge for prey and limit hunting abilities of some predators, but increase prey mortality if predators utilize different microhabitats and hunt with complementary strategies.  We tested whether multiple predator effects influenced an IGP module within experimental pond communities, and examined whether increasing habitat complexity modified the outcome of IGP and MPEs. We additively combined three top predators (central newts [Notophthalmus v. louisianensis], mosquitofish [Gambusia affinis], and dragonfly naiads [Aeshnidae]) with larval ringed (Ambystoma annulatum) and spotted (A. maculatum) salamanders, the latter two of which formed an intraguild predator-prey relationship, respectively.  All predators treatments were crossed the presence/absence of vertical cover to manipulate habitat complexity and trials conducted within experimental pond mesocosms.

Results/Conclusions

Size at metamorphosis of A. annulatum was reduced in the controls and with mosquitofish compared to all other predator combinations.  Survival showed an inverse relationship with size, where survival was higher in the control and mosquitofish treatments than in other predator treatments.  Increased habitat complexity had minimal effects on size or survival of A. annulatum.  Predator treatment, habitat complexity, and the survival of A. annulatum exhibited a three-way interaction that influenced size and survival of A. maculatum.  Survival of A. annulatum and A. maculatum were negatively correlated, indicative of a release from IGP, but the effect varied by predator treatment.  Increased habitat complexity also modified the effect of each predator, and in some cases eliminated the negative relationship between salamanders.  Overall, our results indicate that multiple predator effects and habitat complexity can influence an intraguild predation module by altering the survival of the intraguild predator, with subsequent cascading effects on the survival of the intraguild prey.  Further investigations are necessary into communities with high predator diversity to tease apart how varying habitat conditions and predator composition influence IGP and MPE outcomes, which ultimately will lead to improved understanding of how predation affects community structure and ecosystem function.