Recent predator-prey models have shown that the duration of various life stages, as well as the generation time of the prey relative to the predator, can influence predator-prey dynamics. Depending on the duration of these various stages, the predator-prey interaction can exhibit stability, generation cycles, or multi-generation consumer-resource cycles. To date, there has never been an unambiguous experimental test of how changes in development time of a predator or prey life stage impact predator-prey population dynamics. We conducted a laboratory experiment with the cowpea weevil Callosobruchus maculatus and its parasitoid Anisopteromalus calandrae to assess whether an increase or decrease in the duration of the invulnerable prey stage promoted stable predator-prey temporal population dynamics.
The experiment was conducted in replicate microcosms that were subjected to one of three treatments of the development time of the juvenile stage of the weevil: long-duration (60% increase), short-duration (60% decrease) and control. We manipulated development time, while affecting no other life stage of the host or parasitoid, by replacing beans infested with juvenile weevils of a known age with an equivalent number of beans containing weevils at a younger or older age. The experiment was run for two years (> 30 generations).
Results/Conclusions
Mean weevil abundance was two times higher in the long-duration than short-duration treatment. In contrast, parasitoids were 33% less abundant in the long- than short-duration treatment. Variability in abundance (standard deviation) over the time series, showed a similar pattern. We used wavelet analyses to explore the cyclical behavior of host and parasitoid population dynamics in each experimental microcosm. In the control treatment, hosts, and to a lesser extent parasitoids, exhibited oscillations with a period of 24 d (2 census dates) – a well-known pattern for this study system. However, in the short-duration treatment, weevils and parasitoids exhibited very weak to no evidence of oscillatory behavior. The long-duration treatment showed similar dynamical behavior to the control. Overall, these data suggest that stability (i.e., reduced variability in abundance and loss of cyclic behavior) was enhanced by reducing the duration of the vulnerable host stage while holding all else constant. A model developed specifically for this system by the authors is currently being used to assess long-term stability properties of the experimental treatments. From a pest management perspective, the short-duration treatment achieved low and less variable prey (pest) abundance, suggesting that manipulation of development times may be a possible tactic for pest control.