Variation In Basal Rate Research Articles

The difficulty with correlations: Energy expenditure and brain mass in bats

Brain mass has been suggested to determine a mammal's energy expenditure. This potential dependence is examined in 48 species of bats. A correlation between characters may be direct or derived from shared correlations with intervening factors without a direct interaction. Basal rate of metabolism in these bats increases with brain mass: large brains are more expensive than small brains, and both brain mass and basal rate increase with body mass. Basal rate and brain mass also correlate with food habits in bats. Mass-independent basal rate weakly correlates with mass-independent brain mass, the correlation only accounting for 12% of the variation in basal rate, which disappears when the combined effects of body mass and food habits are deleted. The correlation between basal rate and brain mass seen in this and other studies usually accounts for <10% of the variation in basal rate and often <4%, even when statistically significant, a minimalist explanation for the level the basal rate. This correlation probably reflects the intermediacy of secondary factors, as occurred with food habits in bats. Most biological correlations are complicated and must be examined in detail before assurance can be given as to their bases.

Analysis of factors that influence energy expenditure in honeyeaters (Meliphagidae)

ABSTRACTThe energy expenditure of the tūī (Prosthemadera novaeseelandiae), a meliphagid endemic to New Zealand, was measured and compared with 20 species of honeyeaters (family Meliphagidae) to determine whether its expenditure is influenced either by life in a moist, temperate climate or an island residence. Body mass in the honeyeaters accounted for 91.5% of the variation in basal rate. The combination of body mass, climate and the maximal limit to an altitudinal distribution explained 98.6% of the variation in basal rate with tropical, low-altitude species having the highest mass-independent rate. The basal rates of meliphagids in tropical highlands are similar to those in temperate lowlands, which may reflect similar food supplies. The tūī mass-independent expenditure appears to reflect an active lifestyle in a temperate climate with no evidence that an island residence influenced its rate, whereas sedentary birds on New Zealand have responded to island life with a depressed basal rate. An effective analysis of the variation in energy expenditure requires the inclusion of the ecological and behavioural characteristics that distinguish species.

The ecological energetics of birds in New Guinea

The energetics of 79 species of birds living in greater New Guinea, data for 44 of which are presented here for the first time, is examined to determine the extent to which it reflects the behavior of species and the conditions they encounter in the environment. Body mass alone accounts for 86.6% of the variation in the basal rate of metabolism of these species, whereas the combination of body mass, foraging sub- strate, flightless condition, activity, and life on islands or continents collectively account for 95.2% of its variation. When the passerine/non-passerine dichotomy is added to the analysis, the six factors account for 96.7% of the variation in basal rate. Basal rate also correlates with other factors, including maximal altitude of distribution, torpor, and food habits when individually combined with body mass, but they lose significance when other factors are brought into the analysis. Altitudinal limits to distribution can be included in the analysis only if activity is dropped because of the correlation between these factors. Torpor correlates with an aerial feeding strategy. Food habits correlated with activity level and the passerine/non-passerine dichotomy. The attempt to account for the variation in the energetics of birds by a phylogenetic analysis is inappropriate because the fundamental basis of energetics is physiological with strong behavioral and ecological overtones. Body mass accounts for 90.4% of the variation in thermal conductance. The regulated level of body temperature varies from ca. 39 to 41°C at masses &gt; 100 g, below which it decreases to 37 and 39°C at 10 g, with a few small species having body temperatures as low as 35°C. New Guinea is an important source for the terrestrial avifauna of South Pacific islands. The characteristics of its birds therefore are appropriate standards by which to judge the adjustments occurring in, and required of, birds endemic to these islands.

Physiological correlates of habitat association in East African sunbirds (Nectariniidae)

AbstractEast African sunbirds (Nectariniidae) vary in the degree to which they use open habitats and forest habitats. Species that use open habitats may experience more extreme temperatures and greater exposure to solar radiation than those in forest habitats. Basal rates of metabolism, body temperature and thermal conductance were compared for open habitat‐ and forest‐associated sunbirds from Kibale National Park, Uganda. Variation in basal rate of metabolism was associated with body mass, but there was no difference between forest and open habitat species. Variation in body temperature was not associated with body mass or habitat. Variation in thermal conductance was associated with body mass and habitat; open habitat species were characterized by significantly lower thermal conductances than forest species. Because reduced thermal conductance may decrease energy expenditure at low ambient temperatures and reduce exogenous heat gain at high ambient temperatures, this difference may optimize energy expenditure when temperatures are highly variable. This suggests a mechanism by which physiological characteristics may influence energetic consequences of habitat selection.

Flightless rails endemic to islands have lower energy expenditures and clutch sizes than flighted rails on islands and continents

Data are presented on the standard energetics of six flighted and five flightless species of rails (Aves: Rallidae). The factors influencing these data and those from three additional species available from the literature, one of which was flightless, are examined. Basal rate of metabolism correlates with body mass, residency on islands or continents, volant condition, pectoral muscle mass, and food habits, but not with climate. The greatest capacity (96.2%) to account for the variation in basal rate of metabolism in 15 populations that belong to the 14 species occurs when body mass, volant condition, and food habits are combined. Then flighted species have basal rates that average 1.38 times those of flightless species and herbivorous rails have basal rates that are 1.37 times those of omnivorous species, which means that, independent of body mass, flighted gallinules have basal rates that are 1.9 times those of flightless, omnivorous rails. Distribution, pectoral muscle mass, and flight ability cannot be combined in the same analysis because they code for similar information. The evolution of a flightless condition in rails requires the absence of eutherian predators, but has occurred in the presence of marsupial predators. Each of the six studied flightless rails independently evolved a flightless condition and a low basal rate, whereas the evolution of herbivory and an associated high basal rate evolved at least twice in these species. Flightless rails on islands have clutch sizes that are only about one-half those of flighted rails living on continents, the reduction in clutch size correlating with a reduction in basal rate of metabolism. Thermal conductance in rails is correlated with body mass and food habits: herbivorous rails had conductances that were 1.43 times those of omnivores, i.e., conductances are highest in species with the highest basal rates.

Food habits and the evolution of energetics in birds of paradise (Paradisaeidae)

Basal rates of metabolism, minimal thermal conductances, and body temperatures are reported for 13 species of birds of paradise that belong to nine genera. Body mass alone accounts for 91.7% of the variation in their basal rates. Basal rate in this family also correlates with food habits and the altitudinal limits to distribution. Species that feed almost exclusively on fruit have basal rates that average 79.4% of species in which >10% of the diet is insects, and species restricted to altitudes <1,000 m have basal rates that are 90.6% of those found at higher altitudes. The combination of body mass, food habits, and altitudinal distribution accounts for 99.0% of the variation in basal rate in the species studied. The application of food habits to a cladogram of the studied Paradisaeidae implies that frugivory and low basal rate were plesiomorphic in this family. The evolution of omnivory, defined as including >10% of the diet as insects, appears to have occurred at least twice, and in each case was associated with an increase in basal rate of metabolism. Basal rate increased at least thrice with a movement into the highlands. Basal rate, however, does not correlate with plumage dimorphism or with reproductive behavior. The basal rates of metabolism in manakins and birds of paradise, i.e., passerine frugivores, are greater than those found in nonpasserine frugivores. Thermal conductance correlates with body mass, which accounts for 85.8% of its variation in this family. Body temperature in paradisaeids, the mean of which was 40.2 degrees C, may correlate with basal rate of metabolism.

Standard energetics of leaf-nosed bats (Hipposideridae): its relationship to intermittent- and protracted-foraging tactics in bats and birds.

Basal rates of metabolism within the insectivorous genera Hipposideros and Ascelliscus, Old World leaf-nosed bats (Hipposideridae), ranged from 58% to 77% of the mammalian standard. The larger species, Hipposideros diadema and Hipposideros maggietaylori, effectively thermoregulated at ambient temperatures down to 9 degrees C, whereas two smaller species, Hipposideros galeritus and Hipposideros cervinus, occasionally permitted body temperatures to fall below 32 degrees C. The low basal rates of metabolism in hipposiderids correlated with a predatory life-style characterized by intermittent flight from a perch to capture insects, a correlation similar to that found in nonpasserine birds. Intermittent-foraging bats and nonpasserines collectively had basal rates of metabolism that averaged 75% of those that pursue insects during protracted flight. However, no difference in basal rate was found between protracted- and intermittent-foraging passerines, which had basal rates 1.8- and 2.4-times those of protracted-foraging and intermittent-foraging bats and nonpasserines, respectively. Bats, swifts, and caprimulgids that enter torpor have basal rates that are 85% of those of similar species that do not enter torpor. Body mass, order affiliation, foraging mode, and propensity to enter into torpor collectively account for 97% of the variation in basal rate of metabolism in insectivorous bats and birds. Foraging style therefore appears to be a factor contributing to the diversity in endotherm energetics. Minimal thermal conductance in the genus Hipposideros ranged from 75% to 102% of the mammalian standard. Birds have minimal thermal conductances that are 75% of mammals and intermittent foragers have minimal conductances that are 78% of protracted foragers.

The comparative energetics of ‘caviomorph’ rodents

The energetics of 11 species of New World hystricognath (‘caviomorph’) rodents are presented and compared with data from the literature on 19 additional species. Log 10 body mass alone accounts for 94% of the variation in the log 10 basal rate of metabolism in caviomorphs. The residual variation in basal rate is correlated with the stratum on which species live: arboreal species have low basal rates; terrestrial and fossorial species have intermediate basal rates; and aquatic species have high basal rates. When stratum is not included in the analysis, folivores, especially those that are arboreal, have lower basal rates than species with other food habits when combined with log 10 body mass. Small island endemics, all of which are folivores, have basal rates that are 61% of continental species. Log 10 basal rate correlates with family affiliation when combined with log 10 mass, but only if no other factor is included. Therefore, caviomorphs with low basal rates are arboreal, folivorous, live on small islands and belong to the Capromyidae, whereas other character combinations are associated with higher basal rates. These observations demonstrate that the basal rates of caviomorphs reflect many factor interactions. No differences in basal rate were found to reflect climate. Log 10 mass, the only factor to correlate with conductance, accounts for 82% of the variation in log 10 minimal thermal conductance. Mean interspecific body temperature was 36.9°C; it was lowest in aquatic and fossorial species.

Plasticity of Energetics in Blossom Bats (Pteropodidae): Impact on Distribution

Blossom bats, Macroglossus minimus and Syconycteris australis , from New Guinean lowland rainforests usually enter torpor at low ambient temperatures (11–29°C). Torpid individuals maintain a 2–5°C differential of body temperature above ambient temperature. Individuals from highlands, however, regulate body temperature at 36–37°C at ambient temperatures as low as 13°C. A third species, Melonycteris melanops , exhibits imprecise temperature regulation, but rarely enters torpor. Basal rates of metabolism for lowland populations of the three species are low compared to the mammalian standard, whereas highland and subtropical S. australis and highland M. minimus have basal rates near expected values. Thermal conductances of blossom bats are lower than the mammalian standard, except in subtropical S. australis . The variation in basal rates of metabolism in nec-tarivorous bats correlates with body size and effectiveness of thermoregulation. M. minimus and S. australis have large geographic distributions, ability to cross narrow oceanic water gaps, and sufficient plasticity in energetics to meet demands imposed by environments including small oceanic islands, disturbed successional forests, and primary lowland and montane rain forests.

Temperature Regulation and Rate of Metabolism in Three Bornean Bats

Data are presented on temperature regulation and rate of metabolism in three Bornean bats, Cynopterus brachyotis, Eonycteris spelaea , and Hipposideros galeritus . These species maintain core body temperature at 36.5, 34.0, and 31.9°C, respectively, a sequence also found in the level of basal rate of metabolism, namely 92, 73, and 55% of the values expected from mass, respectively. These data and those available in the literature demonstrate that much of the variation in basal rate among bats correlates with food habits, independent of phylogeny. Thus, Cynopterus , like other frugivorous species, has the highest basal rate reported here, and Hipposideros , an insectivorous species, has a low basal rate. The intermediate basal rate in Eonycteris may reflect a large mass (52 g) for a nectarivorous species. The variation in basal rate may be understood principally in terms of the phenology of foods used. Previous estimates for basal rate of metabolism and minimal thermal conductance of Neotropical bats have been readjusted for temperature and pressure.

Food habits and the basal rate of metabolism in birds.

The correlation of basal rate of metabolism with various factors is examined in birds. Chief among these is body mass. As in mammals, much of the remaining variation in basal rate among birds is associated with food habits. Birds other than passerines that feed on grass, nectar, flying insects, or vertebrates generally have basal rates that are similar to mammals of the same mass and food habits. In contrast, most invertebrate-eating birds that weigh over 100 g have higher basal rates than equally-sized, invertebrate-eating mammals. The high basal rates of small passerines equal those of small mammals that do not enter torpor and represent the minimal cost of continuous endothermy. Large passerines and small procellariiforms, charadriiforms, and psittaciforms generally have higher basal rates than mammals with the same mass and food habits. The high basal rates of passerines (in combination with altricial habits) may have significance in permitting high post-natal growth rates and the exploitation of seasonally abundant resources. These interrelations may contribute to the predominance of passerines in temperate land environments.