Deserts are natural laboratories in which to study the acute effects of extreme heat and aridity on animal physiology, as well as the physiological adaptations that these animals develop to survive. For small, endothermic fliers in the desert, heat balance and water balance are challenging due to high surface area to volume ratios and the additional heat load imposed as a result of endothermy. Much of the previous fifty years of thermo- and hydroregulation research has focused on larger, charismatic megafauna; extremophiles; or only part of the heat or water balance story. Here, I calculate the first heat budget for an important desert bee, Centris caesalpiniae. As is common in many mammals, avians, and other flying insects, I find that C. caesalpiniae males use an appendage – in this case the abdomen – as a convective radiator to dispel excess heat produced by the thoracic flight muscles at high air temperatures. The few heat budgets measured for flying endotherms are conducted in the shade so as to eliminate the effects of solar radiation. To further refine the accuracy of my heat budget model, I consider how heat gain from solar radiation affects the thermal balance of flying desert endotherms. To this effect, I find that solar radiation contributes 43 to 54% of the total heat gain of a desert Centris pallida bee. I additionally show that large morph male, small morph male, and female C. pallida, use different thermoregulatory tactics while flying in shaded versus sunny conditions; large males and females rely on the abdominal convector in the sun while small morph males increase convective conductance in the sun, but do not use an abdominal convector. Given that evaporative cooling was not a significant part of the heat budget for neither C. caesalpiniae nor C. pallida, I investigated the effects of water loss rates and critical thermal maxima during flight on duration of activity period. I found that male C. caesalpiniae limited their activity period due to high water loss rates rather than overheating, and that Centris critical water contents ranged from 48 to 54%, limiting flight activity to about 3 hours.

Stream flow permanence plays a critical role in determining floristic composition, abundance, and diversity in the Sonoran Desert, but questions remain about the effects of stream flow permanence on butterfly composition, abundance, and diversity. Understanding the effects of flow permanence on butterflies and relevant subsets of butterflies (such as butterflies whose host plants are present) and comparing them to these same effects on plants and relevant subsets of plants (such as butterfly nectar plants and larval host plants) provided insight into pollinator and riparian conservation and restoration.

I surveyed four Sonoran desert stream sites, and found significant relationships between flow permanence and plant and butterfly species richness and abundance, as well as strong relationships between plant and butterfly abundance and between plant and butterfly species richness. Most notably, my results pointed to hosted butterflies as a break-out category of butterflies which may more clearly delineate ecological relationships between butterfly and plant abundance and diversity along Sonoran Desert streams; this can inform conservation decisions. Managing for hosted (resident) butterflies will necessarily entail managing for the presence of surface water, nectar forage, varying levels of canopy cover, and plant, nectar plant, and host plant diversity since the relationships between hosted butterfly species richness and/or abundance and all of these variables were significant, both statistically and ecologically.