Dissertation Research: Pattern and Process in Plant Physical Defenses Across a Latitudinal Gradient

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Many plants are eaten by a wide variety of insects, and herbivorous, or plant-eating, insects sometimes consume almost half of the leaves that a plant grows each year. Plants in tropical forests tend to be better defended against being eaten by insects than plants in temperate forests, and the tropical plants are also more diverse. One explanation for both higher diversity and better defense may be that insects eat more leaves in tropical forests than in temperate forests, selecting for plants with more defense and preventing dominance by just a few plant species. However, it is not really known whether herbivory is higher in tropical forests, because no previous studies have measured herbivory in a consistent way across a wide range of latitudes. The goal of this study is to compare the consumption of leaves of plants in the cucumber family by insects in three locations, one tropical (Panama), one subtropical (Florida), and one temperate (Wisconsin). To keep factors such as nutrient content of leaves and local environmental conditions constant, the investigators will grow plants in greenhouses and then transplant them into natural environments at each of the sites. They will then record the number and type of insects visiting the plants, and how much those insects consume of each plant. This will occur over the main growing season of the plants at each site. The study will end when fruits and seeds have been produced, which will reveal how herbivore damage to leaves can influence plant fertility. Understanding how herbivory changes from tropical to temperate climates will help predict how change in climate might change amounts of herbivory in the future. For example, rise in temperature might cause tropical insects to expand into higher latitudes and increase the amount of plants that are eaten in the temperate zone. In the case of insects that eat crops, this could impact agriculture. Knowing more about current patterns of herbivory may help people adapt to future change through measures such as changes in pest control management. This project will also provide research training for undergraduates and conduct outreach to public schools.