Traits controlling body size in copepods: separating general constraints from species-specific strategies

A new synthesis of laboratory measurements of food-saturated development and growth across diverse copepod taxa was conducted in a theoretical framework that distinguishes general allometric constraints on copepod physiology from contingent strategies that correlate with size for other reasons. After temperature correction, the allometry of growth rate is inconsistent between the ontogeny of Calanus spp., where it follows the classic −0.3 power-law scaling, and a broader spectrum of adult size Wₐ (0.3 to 2000 μg C, Oithona spp. to Neocalanus spp.), across which the classic scaling appears to represent only an upper limit. Over the full size spectrum, after temperature correction, a growth rate g₀ relative to the −0.3 power law correlates with adult size better than does relative (temperature-corrected) development rate u0; in contrast, at a finer scale of diversity (among Calanus spp., or among large (>50 μg C) calanoids in general), u₀ is the better correlate with adult size and the effect of g₀ is insignificant. Across all these scales, the ratio of relative growth and development rates g₀/u₀ is a better predictor of adult size than g₀ or u₀ alone, consistent with a simple model of individual growth.