Henry S. Horn - US grants

9520626 Flying insects vary in the metabolic fuels they use to support energetically costly flight. Flies and bees usually use sugars to fuel flight, while moths and butterflies usually use fat stores. This research will examine metabolic physiology at several levels in a hawkmoth whose heavy body, narrow wings and rapid flight impose high flight costs. Measurement of rates of oxygen consumption and carbon dioxide production during flight will indicate whether sugars or fats are being oxidized. Moths that have fed on sugar-rich nectar will be compared with unfed moths to determine whether fuel use varies with nutritional status. Maximum reaction rates of catabolic enzymes in the carbohydrate and lipid burning pathways of flight muscle will be assayed to determine how feeding and flight performance relate to the moth's underlying metabolic biochemistry. Stable isotope analysis will be used to characterize the contribution of larvally-obtained and adult- obtained resources to egg provisioning. The research will improve understanding of the constraints on activity metabolism and the relative importance of metabolic capacity and fuel availability in limiting performance. Improved understanding of the way energy is allocated between flight and reproduction may increase our understanding of the population dynamics of flying insects.

Forests in our landscape are increasingly becoming isolated "islands" in a "sea" of urban, suburban, or agricultural land. For their populations to persist in such a landscape, trees must disperse their seeds from one island to the next. Many trees use the wind to disperse their seeds. In strong winds, especially over a rugged forest canopy or near the edge of a forest, three-dimensional "whirlpools" form with winds that sometimes blow upwards. If the upward velocity of the wind is greater than the rate of fall of the seed, the seed can go up rather than down. It may even get caught in a large updraft, such as happens where warm air rises, or where winds are deflected by a hill, a forest edge, or a large building. Such updrafts can take a seed high into the atmosphere, where it encounters faster winds. Or the updraft itself can move for miles, as it does in a thunderstorm, before letting the seed settle to ground.

This project is a collaboration between biologists and atmospheric scientists to determine how often seeds go into these long-distance modes of dispersal. This will require measuring how strong the wind must be before seeds break loose from the tree, how slowly seeds fall in still air, and how the upward velocity of wind changes in different settings. Finally it will test experimentally whether winds can carry seeds as far as the distance between forest islands. The importance of updrafts for seed dispersal and the frequency of long-distance dispersal will be compared for 18 wind-dispersed tree species of the northeastern United States. Such information is vital for understanding the dynamics of forest species, and for maintaining them as humans increasingly fragment the landscape.