Soil nitrogen mediates the effect of climatic distance on herbivory rates in a tropical herb

The center‐periphery hypothesis predicts that species are most abundant at the center of their distribution range. Differential herbivory rates between center and periphery populations can explain this variation in species abundance. However, if the geographic center of a species distribution coincides with its ecological optimum, the resource availability hypothesis predicts higher herbivory rates and tolerances at the center compared to the periphery. Biogeographical studies on herbivory have treated these two mechanisms separately, limiting our mechanistic understanding of the role of herbivory in shaping species range limits. We analyzed the role of resource availability on herbivory variation from center to periphery using data collected across the distribution of Thunberbia atacorensis, a range‐limited species of West Africa. We used two types of distances: geographic distance (the distance from each plot to the geographic center of all populations) and climatic distance (the distance from each plot to the preferendum of the species). We found no increase in herbivory toward the periphery of the climatic and geographic ranges. However, herbivory rates increased with soil nitrogen. Soil nitrogen decreased from the center to the periphery of the climatic range. Phylogenetic diversity and competition from surrounding plants did not affect herbivory rates. Our study provides insights into how nutrient limitation can shape species center‐periphery distribution by altering spatial variation in herbivory rates. The center‐periphery hypothesis predicts that species are more abundant at the center than the periphery of their range. Therefore, one would thereby expect higher herbivory rates at the periphery than at the center, possibly explaining the capacity of biotic drivers to negatively influence and limit range expansion. Here, we showed that plant nutrient limitation does not favor species’ ability to compensate lost tissue at the periphery and this may ultimately drive species limitation.