Ecological interactions vary geographically, and this variation must be understood in order for us to make robust generalizations about ecological processes.  My laboratory has been investigating latitudinal variation in plant-herbivore interactions in Atlantic Coast salt marshes, asking four questions.  1. Do herbivore densities vary across latitude? 2. Does herbivore damage to plants vary across latitude? 3. Does plant resistance vary across latitude, and if so, what plant traits explain this variation? 4. How does latitudinal variation in competition and predation mediate patterns of herbivory?

Results/Conclusions

Work on a community of common plants and herbivores in Atlantic Coast salt marshes in the U.S., and to a lesser extent a parallel community in Europe, indicates that chewing and galling herbivores are more abundant, and do more damage to plants, at low versus high latitudes.  Low-latitude plants are less palatable to chewing herbivores, due to latitudinal variation in plant toughness, nitrogen content and polar chemistry, and much of this variation is constitutive rather than induced.  Sucking herbivores show little variation in abundance across latitude.  Herbivore densities in the field, and the damage that they do to plants, are likely mediated by complex interactions between climate, herbivore guild, plant quality, competition and predation.