PS 35-71
Herbivory across latitudes: Climatic, edaphic, and trait-based drivers of leaf consumption in Solidago altissima across the Eastern U.S.
Dobzhansky (1950) and others have asserted that biological interactions are more intense in the tropics—that is, a more important determinant of population dynamics than abiotic conditions, particularly compared to climatically harsh high latitude ecosystems. Herbivores, for example, may be able to maintain higher population sizes and thus exert stronger ecological and evolutionary pressures on plants at lower latitudes. Rates of plant consumption by herbivores, however, are also determined by 'bottom-up' processes of plant defensive chemistry and tissue nutrient content, which may be less driven by climate than by edaphic factors. Thus, it is unclear whether actual rates of herbivore consumption—often a key driver of community assembly and ecosystem dynamics—should be predicted by latitude per se. Here, we collected leaves from an old-field dominant species, Solidago altissima L., from 20 sites across ten degrees of latitude in the Eastern United States to determine the percentage leaf area consumed by insect folivores. We obtained soil chemistry and climate data for each site, as well as plant functional and defensive traits, which include specific leaf area (SLA), leaf carbon to nitrogen ratio, and trichome density.
Results/Conclusions
Mean annual temperature, soil nitrogen, and soil phosphorus were positively correlated with whether a leaf was eaten, while trichome density and soil phosphorus were more associated with the extent of leaf consumption. Results suggest that herbivore damage does not vary systematically with latitude, and that climate is a relatively minor driver compared to soil fertility. Given that temperature is negatively associated with latitude while soil nitrogen increases with latitude at our sites, the opposing patterns of climate and soil properties that drive herbivore consumption rates likely explain the lack of overall latitudinal pattern. To our knowledge, this is the first study that has combined the effects of both climatic and fertility gradients in the examination of geographic patterns of herbivory intensity.