“Dragons” on the landscape: Modeling the abundance of large carnivorous dinosaurs of the Upper Jurassic Morrison Formation (USA) and the Upper Cretaceous Dinosaur Park Formation (Canada)

The field metabolic rates (FMRs) of 229 species of terrestrial vertebrates, all measured using the doubly labeled water method in free-living individuals, were evaluated. Daily rates of energy expenditure were as low as 0.23 kJ per day in a small reptile (gecko), to as high as 52 500 kJ per day in a marine mammal (seal). This is a range of nearly six orders of magnitude. More than 70% of the variation in log-transformed data is due to variation in body size (expressed as body mass). Much of the remaining variation is accounted for by thermal physiology, with the endothermic mammals and birds having FMRs that are about 12 and 20 times higher, respectively, than FMRs of equivalent-sized, but ectothermic, reptiles. Variation in log(body mass) within each of these three taxonomic classes accounts for over 94% of the variation in log(FMR), and results from nonlinear regression analyses using untransformed data support this conclusion. However, the range of residual variation in mass-adjusted FMR within classes is still more than sixfold (ratio of highest over lowest). Some of this variation is associated with affiliations with lower taxonomic levels (Infraclass: eutherian vs metatherian mammals; Family: passerine, procellariform and galliform birds vs other birds), some is associated with habitat (especially desert vs nondesert), and some with differences in basic diet preference and foraging mode and season. The scaling slopes for FMR often differ from BMR slopes for the same Class of animals, and most differ from the theoretical slope of 0.75. Differences among slopes and intercepts that were detected using conventional regression analyses were largely confirmed upon reanalysis using Independent Contrasts Analysis to adjust for phylogenetic biases.

Ecosystems exhibit surprising regularities in structure and function across terrestrial and aquatic biomes worldwide. We assembled a global data set for 2260 communities of large mammals, invertebrates, plants, and plankton. We find that predator and prey biomass follow a general scaling law with exponents consistently near ¾. This pervasive pattern implies that the structure of the biomass pyramid becomes increasingly bottom-heavy at higher biomass. Similar exponents are obtained for community production-biomass relations, suggesting conserved links between ecosystem structure and function. These exponents are similar to many body mass allometries, and yet ecosystem scaling emerges independently from individual-level scaling, which is not fully understood. These patterns suggest a greater degree of ecosystem-level organization than previously recognized and a more predictive approach to ecological theory.