ALLOCATION OF ENERGY TO GROWTH AND RESPIRATION IN AVIAN POSTEMBRYONIC DEVELOPMENT

I used published data to test three possible relationships between the allocation of energy to growth (P) and respiration (R) in chicks: (1) a negative relationship stemming from a trade-off between increased allocation for one purpose, resulting in a reduced proportion of energy available for other purposes; (2) a lack of relationship between P and R; and (3) a positive relationship reflecting functional metabolic coupling of P and R. I restricted my analysis to three periods of the chick's postembryonic development, during which the conflict between allocation of energy to P vs. R is most likely to occur: (a) when the greatest proportion of assimilated energy is allocated to growth; (b) when growth rate (in grams per day), or (c) energy allocated to growth (in kilojoules per day) are at absolute maxima. I analyzed the correlation between P and R after accounting for differences in body mass, costs of biosynthesis, mode of development, breeding latitude, and phylogeny. Under assumption of production efficiency of 0.75, the correlations were negative for periods (a) and (b), and statistically insignificant for period (c). When production efficiency of 0.9 was assumed, the correlation remained negative only for period (c), and became statistically insignificant for the other two. I also found that the positive correlation between growth rate and metabolic rate reported by Klaassen and Drent (1991) becomes insignificant when the effect of breeding latitude is removed from their data set. Thus, the results of all analyses support (1) or (2), rather than (3). I conclude that predictions stemming from (1-3) can often be difficult to distinguish, which may account for the inconsistency between the results of different studies in which the relationship between P and R was analyzed.