In general, if an organism becomes twice as large, the overall population of such organisms will halve.
You may find this paper interesting. Among other things, they find that total population metabolism (i.e., individual basal metabolic rate times the population size divided by the area occupied by that population) stays close to constant relative to body mass, when measured across all eukaryotes.
You may find this paper interesting. Among other things, they find that total population metabolism (i.e., individual basal metabolic rate times the population size divided by the area occupied by that population) stays close to constant relative to body mass, when measured across all eukaryotes.