Plant defenses that respond dynamically to herbivory levels, termed inducible resistance, have received increasing interest as a potential mechanism contributing to herbivore population regulation. A variety of studies demonstrate that inducible resistance can affect herbivore population sizes and damage over the short term, yet most studies involving inducible resistance have not linked these effects to longer-term temporal and spatial dynamics of herbivores and plant damage. Spatial processes in particular profoundly impact ecological dynamics in many non-plant-herbivore systems, and limited evidence suggests spatial processes may also be important in interactions between herbivores and plants with inducible resistance. Our objective has been to develop theory that describes the spatially explicit interaction between plants with inducible resistance and the population dynamics of their herbivores. We will present analyses of a suite of plant-herbivore models of increasing ecological specificity. These include a strategic model that describes induction levels in plants, herbivore demography, and herbivore movement. Additional models include multiple herbivores for which competition is mediated via multiple plant defensive pathways. The focus of our model analyses has been translating biological detail of plant induction and herbivore behavior into predicted spatial patterns of herbivore density and plant damage.

Results/Conclusions

We show that time lags and damage thresholds characteristic of induction of anti-herbivore defenses can create variation in herbivore population densities through both demographic and behavioral mechanisms. When time lags in induction primarily alter herbivore birth and death rates, local instabilities can occur. Depending on the form and magnitude of herbivore dispersal, local instabilities can give rise to both coupled and de-coupled variation in population densities across sites. We also show that movement responses of herbivores, coupled with time lags in induction, can create instability via an alternative mechanism that leads to waves of herbivore damage. This pattern manifests as aggregations of herbivores and damage that move among plants. Finally, we present analyses that suggest that variation in multiple defenses across location can lead to complicated patterns of persistence among competing herbivore species. We conclude by discussing implications for empirical plant-herbivore systems using laboratory observations of an agricultural system and a lepidopteron pest.