Biogeographic theory and studies suggest that 1) plant-animal interactions are more intense at lower latitude, and hence 2) plants at lower latitude need to develop a stronger defense against animals, leading to more palatable plants to herbivores at higher latitude. These statements had been supported by a series of studies conducted in the Atlantic Coast salt marshes. We further asked whether increased plant palatability would lead to increased herbivore performance at high latitude.

We conducted both field surveys and laboratory experiments, focusing on 3 plant and 6 herbivore species in 30 salt marsh sites along the US Atlantic Coast. Field surveys showed that high-latitude (more palatable) plants should also have been of higher quality to herbivores. For example, leaf C:N ratio in all 3 plant species decreased toward higher latitudes, consistent with higher leaf chlorophyll and nitrogen contents at high latitudes. In the laboratory, high-latitude plants supported better herbivore performance in 4 out of 6 herbivore species. The geographic region from which herbivores were collected affected herbivore performance in all 6 species, but the pattern was mixed. Our results suggest that more palatable plants at high latitudes may support better herbivore growth, and geographic origin of either plants or herbivores can affect herbivore performance.