Tropical birds are relatively long-lived and produce few offspring, which develop slowly and mature relatively late in life, the slow end of the life-history axis, whereas temperate birds lie at the opposite end of this continuum. We tested the hypothesis that tropical birds have evolved a reduced basal metabolic rate (BMR). We measured BMR of 69 species of tropical birds, the largest data set amassed on metabolic rates of tropical birds, and compared these measurements with 59 estimates of BMR for temperate birds. Our analyses included conventional least squares regression, regressions based on phylogenetic independent contrasts, and a comparison of BMR of 13 phylogenetically matched pairs, one species from the tropics and one from northerly temperate areas. Our triptych showed that tropical birds had a reduced BMR, compelling evidence for a connection between the life history of tropical birds and a slow pace of life. Further, tropical migrants breeding in temperate habitats had a lower BMR than did temperate residents, suggesting that these migrants have physiological traits consistent with a slow pace of life. In addition, we determined that tropical birds had a lower cold-induced peak metabolic rate and thermogenic metabolic scope than temperate species, a finding that is consistent with the hypothesis that their environment has not selected for high levels of thermogenesis, or alternatively, that a slow pace of life may be incompatible with high thermogenic capacity. We conclude that physiological function correlates with the suite of life-history traits.basal metabolic rate ͉ life history ͉ peak metabolic rate ͉ tropics ͉ migration L ife-history traits, such as clutch size, age at maturity, rate of growth of offspring, and longevity tend to cluster in ecological space such that species with long lives produce small numbers of offspring that develop slowly and mature relatively late in life (1-3). At the opposite end of this ''slow-fast'' continuum, organisms have low survival rates coupled with large numbers of offspring that develop rapidly and reach sexual maturity at an early age. Among some species, life-history traits also covary with rate of energy expenditure, the pace of life, such that animals with high rates of reproduction have high energy expenditure, and vice versa (4, 5). Support for the connectivity between life history, especially survivorship, and rate of living comes from studies on fruit flies Drosophila (6), houseflies Musca domestica (7), and nematode worms Caenorhabditis elegans (8), as well as meta-analyses on mammals (2, 9, 10). Although less attention has been given to relationships between life history and metabolism in birds, Trevelyan et al. (11) did show an association between resting metabolic rate in birds and their maximum life span.With small clutches (12-14), slower growth as nestlings (15), long periods when fledglings are dependent on parents (16, 17), and higher rates of adult survival than temperate counterparts (15,(18)(19)(20), tropical birds fall along the slow en...

The interaction of vapor-deposited Al atoms with self-assembled monolayers (SAMs) of HS-(CH(2))(16)-X (X = -OH and -OCH(3)) chemisorbed at polycrystalline Au[111] surfaces was studied using time-of-flight secondary-ion mass spectrometry, X-ray photoelectron spectroscopy, and infrared reflectance spectroscopy. Whereas quantum chemical theory calculations show that Al insertion into the C-C, C-H, C-O, and O-H bonds is favorable energetically, it is observed that deposited Al inserts only with the OH SAM to form an -O-Al-H product. This reaction appears to cease prior to complete -OH consumption, and is followed by formation of a few overlayers of a nonmetallic type of phase and finally deposition of a metallic film. In contrast, for the OCH(3) SAM, the deposited Al atoms partition along two parallel paths: nucleation and growth of an overlayer metal film, and penetration through the OCH(3) SAM to the monolayer/Au interface region. By considering a previous observation that a CH(3) terminal group favors penetration as the dominant initial process, and using theory calculations of Al-molecule interaction energies, we suggest that the competition between the penetration and overlayer film nucleation channels is regulated by small differences in the Al-SAM terminal group interaction energies. These results demonstrate the highly subtle effects of surface structure and composition on the nucleation and growth of metal films on organic surfaces and point to a new perspective on organometallic and metal-solvent interactions.

We have studied the interaction of vapor-deposited Al, Cu, Ag, and Au atoms on a methoxy-terminated self-assembled monolayer (SAM) of HS(CH(2))(16)OCH(3) on polycrystalline Au[111]. Time-of-flight secondary ion mass spectrometry, infrared reflection spectroscopy, and X-ray photoelectron spectroscopy measurements at increasing coverages of metal show that for Cu and Ag deposition at all coverages the metal atoms continuously partition into competitive pathways: penetration through the SAM to the S/substrate interface and solvation-like interaction with the -OCH(3) terminal groups. Deposited Au atoms, however, undergo only continuous penetration, even at high coverages, leaving the SAM "floating" on the Au surface. These results contrast with earlier investigations of Al deposition on a methyl-terminated SAM where metal atom penetration to the Au/S interface ceases abruptly after a approximately 1:1 Al/Au layer has been attained. These observations are interpreted in terms of a thermally activated penetration mechanism involving dynamic formation of diffusion channels in the SAM via hopping of alkanethiolate-metal (RSM-) moieties across the surface. Using supporting quantum chemical calculations, we rationalized the results in terms of the relative heights of the hopping barriers, RSAl > RSAg, RSCu > RSAu, and the magnitudes of the metal-OCH(3) solvation energies.

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