Interacting prey and predator driven trophic instability in a prairie grassland

Background/Question/Methods

Oscillations are ubiquitous to predator-prey interactions, although the root causes of fluctuations – whether they are prey or predator based - can be difficult to determine. Resource based models predict that food availability can create an overshoot of predators initiating instability while predator based models predict that strong selection against palatable species create fluctuations. Testing these two alternatives is difficult as seasonality creates limitations for both at different times of the year and while most studies suggest the consumer model, seasonality tends not to be fully considered. We tested these two alternatives within a prairie food web, examining interactions between plant consumption [prey] and seasonal fluctuations in rodents [predators] over a twelve-month period. Our work combined live-trapping, cafeteria trials, exclosures, feeding trials with captive animals as well as DNA scat analyses to test which species are being eaten and when.

Results/Conclusions

Our results found evidence for both the consumer and resource model at different times of the year. The consumer model was evident during summer/ early autumn with high populations, consumption, prairie diet and damage to monitored plots while the resource model was evident during late autumn/winter where a low population had high consumption of available palatable food while otherwise eating unpalatable non-natives. In conclusion our results suggest that the consumer model ultimately drives the system as exotic species subsidize small mammal populations until seasonal times of plenty where palatable species are voraciously consumed. Seasonality drives resource regulation however and this helps explain the well known phenomenon of cyclic small mammal populations.