Date Published: May 17, 2011
Publisher: Hindawi Publishing Corporation
Author(s): Adam Hartstone-Rose, Jonathan M. G. Perry.
In a recent study, we quantified the scaling of ingested food size (Vb)—the maximum size at which an animal consistently ingests food whole—and found that Vb scaled isometrically between species of captive strepsirrhines. The current study examines the relationship between Vb and body size within species with a focus on the frugivorous Varecia rubra and the folivorous Propithecus coquereli. We found no overlap in Vb between the species (all V. rubra ingested larger pieces of food relative to those eaten by P. coquereli), and least-squares regression of Vb and three different measures of body mass showed no scaling relationship within each species. We believe that this lack of relationship results from the relatively narrow intraspecific body size variation and seemingly patternless individual variation in Vb within species and take this study as further evidence that general scaling questions are best examined interspecifically rather than intraspecifically.
The amount of food processed per day must meet an animal’s metabolic requirements. However, while most features of the chewing system (teeth and jaw muscles) scale in proportion to body size (e.g., [1–3]), metabolic rate does not . If food intake is proportional to chewing anatomy, then this discrepancy causes a metabolic crisis for larger primates . Fortelius  suggested that instead, food intake scales directly with body mass. If so, then the metabolic needs of large primates will be met (and exceeded).
Last recorded (ML) maximum (MM) and average (MX) body masses are reported in Table 1.
The scaling patterns so clearly visible when regressing maximum ingested food sizes (Vb) against body mass in a taxonomically diverse sample disappear when the focus sharpens to the intraspecific, at least within these two species. The Vb values between the two populations examined in this study (eight individuals each of Propithecus coquereli and Varecia rubra—the former highly folivorous and the latter highly frugivorous) differ greatly between species; here, there is no overlap in Vb for any of the three foods examined in this study. However, no statistically significant scaling patterns exist within the species regardless of the body size measurement used. In future studies of masticatory anatomy, especially those examining Vb, we recommend examination of broad interspecific samples that span wide body size ranges and that include large sample sizes for each species. Perhaps we are observing a difference in how selection acts on variation between species versus between individuals; perhaps we are observing differences between evolutionary and developmental or structural constraints on the masticatory system, and/or perhaps we are observing an effect of captivity that manifests more strongly at the intraspecific level. Much more work is needed before we can fairly evaluate these possibilities.