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 degrees C; it was lowest in aquatic and fossorial species.