Are micronutrients important in structuring plant and herbivore communities? A test in coastal tallgrass prairies.

Radford University, Radford VA

Investigators

Abstract

Understanding what controls herbivore communities is important because of the role that they play in the food web, by eating plants as well as serving as food for higher trophic levels. In addition, many herbivores are pests that eat agricultural plants or compete with livestock for food in rangelands. Past research has focused on three factors that might control herbivore communities: 1) the total amount of plant material available for them to eat, 2) the number of different types of plants available for them to eat, and 3) how much nitrogen and phosphorus (two important nutrients known to be important to herbivore growth) is available in plant material. However, knowing these three things about a particular location has not proved to be enough information to allow scientists to accurately predict how many and what type of herbivores will be present. Recent research has suggested the possibility that other micronutrients such as calcium, potassium, and sodium may help explain how herbivore communities are structured. In the past, scientists thought that these other nutrients were common enough in all plants that they would not affect herbivores. This research will test the hypothesis that some of these micronutrients help to determine the identity and densities of herbivore communities. If this hypothesis is supported, it will suggest novel explanations for what controls herbivore abundance and species composition, which may be helpful for agricultural applications. Soil micronutrients may benefit or harm herbivores directly (by affecting plant food quality) or indirectly (by altering plant community composition). Preliminary data from a coastal tallgrass prairie in Texas showed that foliar micronutrients were better predictors of herbivore community structure than were plant biomass, diversity or macronutrients, and that soil micronutrient concentration affected feeding of grasshoppers when host plant identity was held constant. This project will support a large, multi-factorial field experiment in a coastal tallgrass prairie located south of Houston that will rigorously test the importance of micronutrients in mediating herbivore abundance and diversity, and determine if the importance of micronutrients 1) depends on macronutrients and 2) varies among herbivore feeding modes and guilds. Complementary mesocosm and laboratory experiments will test potential mechanisms of micronutrient effects; that is, whether micronutrients affect herbivores directly or indirectly. This study will be the first to manipulate macro- and micronutrients in concert for understanding insect community structure, and will do so in the field at an unprecedented scale.