Energetic Consequences for a Northern, Range-Edge Lizard Population

Lizards at the northern, cool edge of their geographic range in the northern hemisphere should encounter environmental conditions that differ from those living near the core of their range. To better understand how modest climate differences affect lizard energetics, we compared daily feeding and metabolism rates of individual Sceloporus occidentalis in two populations during mid-summer. Chuckanut Beach (CB) was a cool, maritime climate in northern Washington State, and Sondino Ranch (SR) was a warmer, drier climate in southern, inland Washington. We found no difference between populations in daily energy expenditure (DEE), as calculated from doubly labeled water estimates. The CB population, however, had significantly higher prey availability and rate of daily energy intake (DEI) as estimated from fecal pellet masses. Consequently, CB lizards had higher size-adjusted body masses than lizards from SR. Within CB, during midsummer, DEE was similar to DEI. Within the SR population, DEE trended higher than DEI during midsummer, but was not significantly different. We found no population differences in lizard activity, active body temperature, or preferred body temperature. Hence, we infer the longer activity season for the SR population may compensate for the low food availability and high daily energy cost of midsummer. Moreover, for the CB population, we infer that cooler temperatures and higher food availability allow the lizards to compensate for the shorter activity. We also suggest the CB population may benefit from the predicted warmer temperatures associated with climate change given the similar activity-period body temperatures and DEE between these lizard populations assuming food availability is sufficient

Ventilation, Gas Exchange, and Aerobic Scope in a Small Monitor Lizard, Varanus gilleni

Standard rates of 02 consumption (Vo2) in the dark of Varanus gi/leni (mean mass = 30 g) were measured at 25, 31, 34, and 37 C. At 37 C, the mean value (195 ml 02 STPD kg-1 h-1) was 22% lower than that predicted by a regression equation for lizards as a group (Bennett and Dawson 1976). Despite appearing to be asleep, three- to fourfold elevations in standard Vo2 were seen in lizards with lightweight, transparent respiratory masks. Vo2 was also measured during treadmill exercise at speeds from 5 to 15 m min-1 and during bouts of maximal exercise. Varanus gilleni has the highest factorial aerobic scope (27.5) of any lizard examined to date. The cost of transport in V.gi/leni is relatively high and may relate to short limb length. Pulmonary ventilation and gas exchange (VE, Vo2, Vco2) were simultaneously measured at 25 C, during warming from 25 to 35 C, and again after several hours at 35 C. Air-convection requirements for C02 and 02 were independent of temperature. The patterns of lung ventilation suggest that arterial Pco2 and pH are constant with rising temperature, behavior that is common to that in large varanids and in contrast to that in other reptiles

Charts relating the compressive buckling stress of longitudinally supported plates to the effective deflectional and rotational stiffness of the supports

A stability analysis is made of a long flat rectangular plate subjected to a uniform longitudinal compressive stress and supported along its longitudinal edges and along one or more longitudinal lines by elastic line supports. The elastic supports possess deflectional and rotational stiffness. Such configuration is an idealization of the compression cover skin and internal structure of a wing and tail surfaces. The results of the analysis are presented in the form of charts in which the buckling-stress coefficient is plotted against the buckle length of the plate for a wide range of support stiffnesses. The charts make possible the determination of the compressive buckling stress of plates supported by members whose stiffness may or may not be defined by elementary beam bending and twisting theory but yet whose effective restraint is amenable to evaluation. The deflectional and rotational stiffness provided by longitudinal stiffeners and full-depth webs is discussed and numerical examples are given to illustrate the application of the charts to the design of wing structures

Structures for Reentry Heating

The basic structural approaches for dealing with reentry heating of manned vehicles are summarized. The weight and development status of both radiative and ablative shields are given and the application of these shields to various vehicles is indicated