20 research outputs found
What causes intraspecific variation in resting metabolic rate and what are its ecological consequences?
Individual differences in the energy cost of self-maintenance (resting metabolic rate, RMR) are substantial and the focus of an emerging research area. These differences may influence fitness because self-maintenance is considered as a life-history component along with growth and reproduction. In this review, we ask why do some individuals have two to three times the GÇÿmaintenance costsGÇÖ of conspecifics, and what are the fitness consequences? Using evidence from a range of species, we demonstrate that diverse factors, such as genotypes, maternal effects, early developmental conditions and personality differences contribute to variation in individual RMR. We review evidence that RMR is linked with fitness, showing correlations with traits such as growth and survival. However, these relationships are modulated by environmental conditions (e.g. food supply), suggesting that the fitness consequences of a given RMR may be context-dependent. Then, using empirical examples, we discuss broad-scale reasons why variation in RMR might persist in natural populations, including the role of both spatial and temporal variation in selection pressures and trans-generational effects. To conclude, we discuss experimental approaches that will enable more rigorous examination of the causes and consequences of individual variation in this key physiological trait
Characterizing developing adverse pressure gradient flows subject to surface roughness
An experimental study was conducted to
examine the effects of surface roughness and adverse
pressure gradient (APG) on the development of a turbulent
boundary layer. Hot-wire anemometry measurements were
carried out using single and X-wire probes in all regions of
a developing APG flow in an open return wind tunnel test
section. The same experimental conditions (i.e., T?, Uref,
and Cp) were maintained for smooth, k? = 0, and rough,
k? = 41–60, surfaces with Reynolds number based on
momentum thickness, 3,000\Reh\40,000. The experiment
was carefully designed such that the x-dependence in
the flow field was known. Despite this fact, only a very
small region of the boundary layer showed a balance of the
various terms in the integrated boundary layer equation.
The skin friction computed from this technique showed up
to a 58% increase due to the surface roughness. Various
equilibrium parameters were studied and the effect of
roughness was investigated. The generated flow was not in
equilibrium according to the Clauser (J Aero Sci 21:91–
108, 1954) definition due to its developing nature. After a
development region, the flow reached the equilibrium
condition as defined by Castillo and George (2001), where
K = const, is the pressure gradient parameter. Moreover, it
was found that this equilibrium condition can be used to
classify developing APG flows. Furthermore, the Zagarola
and Smits (J Fluid Mech 373:33–79, 1998a) scaling of the
mean velocity deficit, U?d*/d, can also be used as a criteria
to classify developing APG flows which supports the
equilibrium condition of Castillo and George (2001). With
this information a ‘full APG region’ was defined