Micrometeorology and Energy Exchange in Two Desert Arthropods

TL;DR: Incoming solar, net, and reflected radiation, wind velocity, relative humidity, and temperatures at various levels above and below an open desert surface were recorded simultaneously at 30—minute intervals for a 3—day period to solve inherent problems in the estimation of contributing factors to net energy exchange and comparison of similar budgets for mesic arthropods are discussed.

Abstract: Incoming solar, net, and reflected radiation, wind velocity, relative humidity, and temperatures at various levels above and below an open desert surface were recorded simultaneously at 30—minute intervals for a 3—day period. Concurrent measurements were also made of arthropod burrow temperatures and relative humidities, scorpion body temperatures, and body and subelytral temperatures of tenebrionid beetles. The burrowing habit enabled arthropods to escape the hot, desiccating conditions recorded on the desert surface during the day. Temperatures and humidities to which scorpions were subjected while in their subterranean retreats depended upon the burrow's depth and subsequent movements in the burrow. Vertical movements between the surface and maximum burrow depths during a 24—hour period provided arthropods with a wide choice of micro— environments. Tenebrionid beetles on the surface were able to achieve a temperature equilibrium only under low temperature and radiation loads. Subelytral cavity temperatures in black Eleodes armata were generally 2—7°C warmer than body temperatures after exposure to direct sunlight. Temperature differences between subelytral cavities of black beetles and beetles with their elytra painted white were small, but suggested that a white dorsal surface was, at least, paritally effective in reducing absorption of solar radiation. The subelytral cavity, in addition to reducing transpiratory water loss, apparently provides a mechanism for increasing convective cooling, and may serve as a temperature “buffer zone” against heat conduction resulting from high intensity solar radiation. A heat exchange budget was estimated for E. armata on the desrt surface. Major contributing factors were heat gained from incoming radiation versus heat lost from convection and reradiation. Contributions from evaporation and metabolism, as determined by laboratory experiments, were very small in comparison, while the role of conduction in energy exchange was assumed to be negligible. Inherent problems in the estimation of contributing factors to net energy exchange, and comparison of similar budgets for mesic arthropods are discussed.